By: Denise M. Gardner
While in the midst of harvest (and all the craziness that comes with it), I thought I’d take a week to remind people about proper cleaning techniques, improving sanitation, and why these two operations are essential for wineries.
I know many of you are ready to close this page now, but WAIT!
I have heard many excuses for short cutting on cleaning over the years. Do any of the following sound familiar?
- There is not enough time in the day to properly sanitize.
- There are not enough employees to do all the work to properly clean.
- Cleaning would take all night to complete properly.
- It’s not necessary to clean/sanitize with wine.
- The wine will sell anyway.
- Cleaning and sanitizing does not actually improve wine quality.
- Sanitation is not really important.
- Proper cleaning does not increase the price in which the wine can be sold.
If you or any of your employees have used at least one of these statements in the past, you could be suffering from poor cleaning and sanitation practices!
In all seriousness, having good cleaning and sanitation procedures can actually save the winery time and money in the long run.
In the height of harvest, I’m sure this is a tough sell. But let’s consider some of these practical cleaning and sanitation suggestions for small, commercial wineries.
On the same page with cleaning vs. sanitizing
Let’s start with a review of definitions, as it can get very confusing. Below are some general definitions taken from a series of sources (Fugelsang and Edwards 2007, Iland et al. 2007, Iland et al. 2012, Solis et al. 2013) to explain the differences between cleaning, sanitation, and sterilization.
- Cleaning – the physical removal of dirt, debris or unwanted material (solid or liquid) from a surface
- Sanitizing – a 99.9% (3 log) reduction of microorganisms
- Sterilizing – the complete removal or inactivation of microorganisms
The wine industry is primarily focused on cleaning and sanitation protocols, as there are not many sterile practices utilized in winery operations (unless you are one of the lucky few wineries bottling aseptically). Even if processors are using sterile filtration to remove yeast and bacteria from the wine, once the wine exits the filter, it comes in contact with equipment that is only sanitized (hopefully!).
Additionally, wine bottles or packages are not sterile when being filled. Even new bottles can contain yeast or bacteria that can potentially contaminate a finished wine. Hopefully, proper sulfur dioxide levels should keep this microorganisms at bay.
For all of these reasons, as the wine has the opportunity to come in contact with existing microflora on processing equipment, wine is bottled in a sanitized environment.
Remember proper sanitation is primarily having good cleaning protocols. Cleaning should always precede sanitation. Failure to physically remove all of the debris from equipment, results in an inability to properly conduct sanitation procedures.
There are several different detergents (cleaners) and sanitizers that wineries can use effectively. Example sanitizers include quarternary ammonium compounds (QUATS), peroxyacetic acid, chlorine dioxide, hot water, and steam. Additionally, wineries can find use in an acidulated (citric acid) sulfur dioxide mixture. However, all sanitizers should be selected specifically for the job at hand (Iland et al., 2012) with consideration towards the microbes that one is trying to avoid.
Most commercial wineries can really focus on improving cleaning practices to provide a step in the right direction towards improving quality and sanitation practices inside the winery.
If you think you may need some help in obtaining winery sanitation basics, please refer to this Northern Grapes Webinar by Randy Worobo on YouTube. Or check out this PodCast by Hans Walter-Peterson and Chris Gerling from Cornell: Winery Sanitation Presspad Podcast, which focuses on preparation for harvest and including sanitation in that prep.
Cleaning harvesting equipment
While this is usually one of the places winemakers feel most complacent about, I would argue that this can be one of the most important places to take care in your cleaning and sanitation practices.
- There is a lot of effort that goes into the growing season in order to adequately ripen wine grapes for many sensory nuances. Additionally, the vineyard is the source of many microorganisms that enter the crush pad and cellar. [For those that use mechanical harvesters, do not forget cleaning and sanitation of this vital piece of equipment (Pregler 2011).] Giving the grapes a clean surface to encounter upon entering the winery ensures that all of that hard work is truly appreciated and preserved from the start of fermentation.
- Without proper cleaning and sanitation practices, you are likely increasing the microbial populations of your wine before it even gets a chance to ferment. Think about it. After crushing/destemming a lot of rotting Pinot Grigio, Pinot Noir, or botrysized Riesling, how many people spray down the equipment (lightly) and move onto crushing the next lot of fruit even if the second lot is cleaner than the first? Sometimes, the order of grape crushing cannot be avoided. But how it is handled upon receiving can be altered. If this is the case for your winery, and you are avoiding good cleaning and sanitation steps in between lots of fruit, you are cross contaminating your juice with, not only yeast and bacteria present in the rotted fruit, but also residual enzymes, proteins, and other by products that can alter wine chemistry in the clean fruit that follows. Think about the potential production problems this can cause later on down the road: laccase browning, acetic acid development, off-flavor development, etc. If such problems arise, it can cause labor and financial investment at a later time.
- Residual foodstuffs (e.g., old grape skins, rice hulls, pulp) can contribute to off flavors within the finished wine. Recent research has shown that there is potential for aromatically-intense varieties (i.e., Niagara, Concord, or Noiret) to leach their flavor compounds into more neutral varieties through absorption and diffusion of equipment-based plastic components that come in contact with the juice and wine (Smith 2014). It is also possible for alien material (i.e., green matter, old rice hulls, and stuck fruit) to contribute to flavors in the final product that may be undesirable or challenging to fix.
- Remember that rice hulls are a pressing aid primarily used for A) hard-to-press varieties to increase yield or B) bulk operations in which pressing time is of the essence. Previous studies, such as the one found here, have shown a detriment in flavor and quality of wines pressed with rice hulls for certain varieties. Additionally, rice hulls can be difficult to remove from the wine press and create potential microbial infection sites for later grapes/juice/wine. It is recommended that the use of rice hulls be on aromatically intense or difficult-to-press varieties (e.g., many native varieties). Use of rice hulls in grapes that have a lot of rot will not only help increase yield of the fruit, but also increase extraction and retention of rot byproducts, which can contribute to off-flavor development.
- Proper cleaning can help maintain your equipment longer. Over time, plant material can slowly degrade equipment. Doing a little scrubbing and properly sanitizing repeatedly can help keep your equipment in relatively good condition. Additionally, the longer debris is left on equipment, the harder it is to remove.
Properly maintaining harvest equipment also leads a good example for all of the other equipment in the winery.
Tanks, Barrels and Bottles
These are places in the cellar where it can get easy to take short cuts as opposed to properly cleaning or sanitizing equipment.
These are places in the cellar where it can get easy to take short cuts as opposed to properly cleaning or sanitizing equipment.
- Remember that tartrate build up in tanks and barrels can make it difficult to properly sanitize the covered portion of the tank/barrel. Make sure to first dissolve large tartrate deposits with hot water before going through a cleaning and sanitation cycle. Without dissolving tartrates, the equipment is not going to get properly cleaned or sanitized.
- When getting ready to fill a tank, remember to run a sanitizer through the tank first to minimize microbial populations on the interior surfaces that come in contact with the wine. This helps ensure varietal flavor nuance and minimizes the risk for spoilage. [Note: Some sanitizers are no-rinse sanitizers and do not require a rinse after the sanitation chemical is applied. Other sanitizers may require a rinse following application. Always check the directions pertaining to your sanitizer carefully before use to ensure it is being used properly for best efficacy, and always use proper protective clothing when handling sanitizer agents.]
- Minimize harboring sites for insects and microbes within the cellar are a practice that can be done at the end of every shift. During harvest, one big problem I see is dripping, dried juice or wine on the exterior of tanks or fermentation bins. While this doesn’t seem like a big deal, it’s an attractive site for fruit flies, which also makes them attractive deposits for spoilage yeast and bacteria. The objective of removing these places of dried juice/wine is to minimize insect infestation in the winery and avoid potential contamination of clean wines.
- Barrels need cleaned prior to sanitation regimes like other pieces of equipment. Many barrel cleaning systems are automatic and can be an efficient way to clean the interior of barrels.
- Barrels are porous and have a lot of grooves inside of them, which can make it difficult to properly clean and sanitize. It is important to note that due to the nature of the barrel, it cannot be sanitized in a way that a stainless steel tank can be sanitized. However, there are many different cleaning and sanitation options for barrels out there, some of which are explored in this Appellation Cornell newsletter from 2013. This study evaluated natural barrel microflora (yeast, including Zygosaccharomyces and Brettanomyces) before and after a sanitation regime was conducted.
- Sulfur wicks are a good way to treat the interior surface of the barrel, but this practice does not penetrate into the interior of the wooden staves (Iland et al. 2007). Also, ensure that the wick is not submerged below any left over water at the bottom of the barrel, as it may extinguish the wick (Iland et al. 2007). Make sure the bung is tightly sealed for best efficacy of a sulfur wick (Rieger 2015).
- Bottling lines are not immune to cleaning. In the food industry, it is commonly noted that most contamination comes from the environment in which the food is processed. This can happen in wine processing, as well. Dust on the bottling line can harbor yeast and bacteria that can be disturbed or moved into the air during large movements, like when bottling a finished wine. Keeping the bottling line clean is a good way to help minimize contamination during bottling operations.
Small Steps That a Commercial Winery Can Take to Improve Cleaning and Sanitation
Being a smaller or boutique sized winery can definitely have its advantages in the cleaning and sanitation world. It’s easy to get creative in terms of improving efficiency, use of, and efficacy of cleaning and sanitation practices. Below are some practical solutions for wineries struggling to incorporate cleaning and sanitation practices in the winery.
Use brushes, like Perfex brushes, to properly scrub equipment during cleaning operations. These are especially helpful when getting that pesky debris off of processing equipment.
Color code brushes or cleaning materials to emphasize their use and make it easier on your employees. By keeping the necessary supplies handy and easy to use, efficiency is likely to improve, which can actually help improve the quality of cleaning operations. Typically, white brushes are reserved for food-contact surfaces (the part of the equipment that actually comes in touch with food) during sanitation steps. Yellow brushes can be used for environmental cleaning (non-food-contact surfaces like the exterior of tanks). Other colors can be purchased for additional specific purposes: detergent only, sanitizer only, etc. Keep the brushes handy during all processing operations.
There is a great article from Food Engineering on the power of color coordination in the food industry, which you can read here.
Consider keeping your cleaning and sanitation system on wheels. While in Oregon, I found it clever how larger wineries kept their fittings on mobile units to aid in availability, cleaning, and organization (Figure 3). While this concept may be helpful to some wineries, I think it can also be applied to cleaning materials. Keeping cleaning materials isolated to a mobile until allows for quick use and organization throughout the entire production facility and minimizes needless travel time to walk back and forth towards where supplies may be kept. Examples, below, for how to improve mobility of your cleaning supplies are given in Figure 4.
You do not need to use fancy (or expensive!) cleaners or sanitizers all of the time in the winery. For quick clean ups, use warm water mixed with potassium carbonate to get stuck or sticky material off of equipment. Use with caution as it can get slippery!
Follow a potassium carbonate rinse with a warm water rinse to remove the solution from equipment and environmental surfaces.
Acidulated sulfur dioxide (Figure 5) can act as a quick sanitizer as well, and is easy to make up and use in the winery. Plus, citric acid, sulfur dioxide, and water are found in wine and will not have an effect on wine quality or flavor.
Finally, I always recommend wineries keep a supply of 70% ethanol in a spray bottle handy for quick cleaning solutions. Ethanol can be used to clean up small spills, quickly rinse sampling valves before and after sampling, or act as an exterior sanitizer towards things like wine thieves, sampling pipettes, and lab benches where one is running analysis. This is an easy chemical to keep on a mobile cart or scattered throughout the winery. However, be sure to purchase food grade ethanol from a chemical supplier and dilute down to ~70% with non-chlorinated water.
Cleaning up at the end of a processing day makes the start up for the next processing day a lot easier. If the equipment is clean to start, then all you have to do is run a quick sanitizer through the equipment before the start of processing operations.
Use hot water to rinse your equipment and make sure your hose has good pressure. Cold water is definitely energy efficient, however, hot water can help remove a lot of debris quicker and make any potential scrubbing easier. Be cautious of the metal on equipment heating up with use of hot water. Also, increasing hose pressure can help dislodge any debris from equipment, which can save time during cleaning operations.
On large processing days (those days when 3 or 4 varieties are being crushed at the winery), designate the day to processing and wait until the next day to complete other operations that can be delayed. Now, some flexibility needs to be made for things like punch downs or pump overs. However, teamwork is key: punch down time can be reduced if there is more than one punch down tool available for employees to use. Juice analysis (pH, TA, Brix, and YAN) is time sensitive, because if the juice starts going through spontaneous fermentation, the results of these chemical indices will change. However, obtaining all of the juice samples from all lots of incoming fruit before starting analysis can save your employees time and avoid splitting up duties during a processing day. With 3 employees, one person could run analyses while the remaining 2 finish cleaning up at the end of a processing day. Reserve racking or moving wines for days when a little less is going on in the cellar unless it is absolutely necessary to open up space in tanks for incoming fruit.
Minimize barrel-to-barrel or tank-to-tank contamination by having small sanitation vessels/buckets (filled with sanitizer) handy and isolated for cleaning/sanitation use. Use a bucket filled with acidulated sulfur dioxide solution to submerge (and fill) your wine thief in prior and after each barrel sample. For smaller samples, consider using one-time-use or disposable pipettes (Figure 6). If you have a 70% ethanol solution in a spray bottle, the metal fittings at the end of hoses can be quickly sprayed in between barrels when transferring barreled wine into a tank or transferring wine from a tank into barrels to help minimize cross contamination (Illand et al. 2007).
Check to see how clean your equipment is with quick testing strips like Pro-Clean Protein Residual testing strip by Hygiena. These testing strips are a good indicator on how well your cellar crew is cleaning equipment. The problem with protein test strips, like the one shown, is that it will detect all organic matter (Iland et al., 2007). It does not represent live or viable microorganisms; there are rapid tests available that may be more representative of microorganism populations.
The video below indicates the ease in which these are to use:
Other options include luminometers like Hygiena’s SystemSURE Plus or 3M Clean-Trace (Rieger 2015), which are also non-specific, but can indicate the cleanliness of a contact surface that is swabbed properly.
While cleaning and sanitation may seem arduous, most wine quality problems I encounter – including funky off-flavors that are challenging to identify, presence of VA, large quantities of wine affected by cork taint, and lack of varietal character – could be primarily avoided with more routine and better cleaning operations. Improving cleaning and sanitation operations can be a step in the right direction for wineries to improve quality associated with their business.
Iland, P., N. Bruer, A. Ewart, A. Markides, and J. Sitters. 2012. Monitoring the winemaking process from grapes to wine: techniques and concepts. 2nd Ed. Patrick Iland Wine Promotions Pty Ltd. Campbelltown, Australia. ISBN: 978-0-9581605-6-8.
Iland, P., P. Grbin, M. Grinbergs, L. Schmidtke, and A. Soden. 2007. Microbiological analysis of grapes and wine: techniques and concepts. Patrick Iland Wine Promotions Pty Ltd. Campbelltown, Australia. ISBN: 978-0-9581605-3-7.
Pregler, B. Nov 2011. Industry Roundtable: Cellar Sanitation. Wine Business Monthly.
Rieger, T. Oct 2015. Microbial Monitoring and Winery Sanitation Practices for Quality Control. Wine Business Monthly.
Smith, JC. 2014. Investigating the Inadvertent Transfer of Vitis labrusca Associated Odors to Vitis vinifera Wines. Retrieved from Electronic Theses and Dissertations for Graduate School: Penn State: https://etda.libraries.psu.edu/catalog/23501.
Solis, M.L.A.A., C. Gerling, and R. Worobo. 2013. Sanitation of Wine Cooperage using Five Different Treatment Methods: an In Vivo Study. Appellation Cornell. 2013-3.
By: Andy Muza, Penn State Extension – Erie County
Another harvest will soon be over for grape growers in Pennsylvania and the winter season is fast approaching. Take the time this winter to explore the resources below to prepare for next season’s pest problems.
The following 5 references provide information on identification and management of insect, disease and weed problems in vineyards. I suggest purchasing these items before next season begins. Although the cost will be over $250 it is well worth having these invaluable resources in your viticultural library.
- New York and Pennsylvania Pest Management Guidelines for Grapes: Every commercial grape grower in Pennsylvania should have a copy of the current guidelines. This guideline provides a wealth of information on insect, disease and weed management with pesticide options, rates, and schedules, as well as, a chapter on sprayer technology.
- A Pocket Guide for Grape IPM Scouting of Grapes in North Central & Eastern U.S.:This pocket reference book is for use while scouting in the vineyard. The guide provides concise information and color photographs on insect/mite pests, natural enemies, diseases and disorders.
- Compendium of Grape Diseases, Disorders, and Pests, Second Edition: This new edition is an expanded version of the original Compendium with 375 photos and drawings and containing updated information about pathogens including additional diseases. The second edition is divided into 4 parts covering: diseases caused by biotic factors (e.g., fungi, bacteria, viruses etc.); disease – like symptoms caused by insects and mites; disorders caused by abiotic factors (e.g., environmental stresses, nutritional disorders, etc.); and fungicides/spray technology.
- Weeds of the Northeast: Described as the first comprehensive weed identification manual available for the Northeast enabling identification of almost 300 common and economically important weeds in the region. The manual contains color photos of vegetative and flowering stages of weeds, as well as, seed photos.
- Wine Grape Production Guide for Eastern North America: A comprehensive reference on all aspects of wine grape production (e.g., varieties, canopy management, nutrient management, etc.) including chapters on disease management, insect and mite pests and vineyard weed management.
Insect and Disease Resources – 2016 articles
Articles from the 2016 season that should be reviewed include:
- 2016 Pre-Bloom Disease Management Review by Bryan Hed, Penn State University
- 2016 Post Bloom Disease Management Review by Bryan Hed, Penn State University
- Late summer/early fall grape disease control; 2016 by Bryan Hed, Penn State University
GRAPE DISEASE CONTROL, 2016 by Wayne F. Wilcox, Cornell University (74 pages). Dr. Wilcox provides comprehensive coverage of relative research and disease management options.
Grape Insect and Mite Pests – 2016 Field Season by Greg Loeb, Cornell University (21 pages). Dr. Loeb provides a thorough review of insect pests that you might see throughout the season in the vineyard. Included are 18 photos of pests/injury along with management guidelines.
Insect and Disease Resources – Web sites
IPM –Grapes (Cornell): Information is available on diseases, insect and mites, weeds, wildlife, organic IPM, spray technology and pesticides.
NYS IPM : Fruit IPM Fact Sheets (Cornell): Fact sheets on diseases and insects on grapes, tree fruit and small fruit. A total of 22 fact sheets pertain to insects and diseases on grapes.
Identifying Grape Insects (Michigan State University): The information on this site is from the previously mentioned resource, A Pocket Guide for Grape IPM Scouting of Grapes in North Central & Eastern U.S. and is categorized by: Pests attacking; buds, leaves, fruit, root, during harvest. Also includes beneficial insects and mites.
Mid Atlantic Vineyards Grape IPM (Virginia Tech): Insect fact sheets categorized by: direct pests – fruit; indirect pests – leaves; trunk and cane feeders; and root feeders.
Ontario Grape IPM: This site provides information on a variety of topics including: insects and mites; diseases and disorders; weeds; herbicide injury; identification keys; etc.
Growing Grapes – Vineyard IPM (eXtension): Articles both in English and Spanish on: insects, diseases, weeds, animal pests and problems not caused by insects or diseases.
Weed Resources – Web sites
New Jersey Weed Gallery (Rutgers): Photos and descriptions of weeds found in New Jersey. Weeds can be viewed by common name, Latin name or thumbnail images.
Weed Identification Guide (Virginia Tech): These pages are intended to aide in the identification of common weeds and weed seedlings found throughout Virginia and the Southeastern U.S. The weed pictures are arranged alphabetically by common name.
UMass Extension Weed Herbarium (University of Massachusetts): Identification notes and color photos of over 500 weeds.
UC-IPM Weed Photo Gallery (University of California): Common names link to pages with weed descriptions and photos often showing several stages of development.
By: Denise M. Gardner
Based on the number of questions I have received this year about yeast assimilable nitrogen (YAN), it looks like more winemakers are taking it upon themselves to measure YAN on pre-harvested fruit or on incoming juice. This can be a great step in improving wine quality! Measuring YAN offers several benefits to winemakers, including:
- Minimizing the incidence of hydrogen sulfide development in the wine.
- Enhancing varietal character by producing cleaner wines with adequate and specific nitrogen supplementation throughout primary fermentation.
- Minimizing excessive nutrient supplementations, in which left-over nitrogen (after primary fermentation) may act as nutrient sources for spoilage yeast and bacteria.
- Reducing unnecessary work for your employees by minimizing problematic production situations (e., fixing wines with hydrogen sulfide). Such actions could have economic benefit (i.e., reduction in supplies, reduction in time/labor)
Below is a quick refresher for those that may have questions about YAN.
- YAN = Ammonia Concentration + Primary Amino Acid Concentration given in the units: mg N/L (read: milligrams of nitrogen per liter)
- Most suppliers (g., Lallemand, Scott Labs, Enartis, Laffort) will provide recommendations on what to add in low, medium, or high YAN situations. Make sure you consult your handbooks or supplier websites for their product-specific recommendations.
- At the start of fermentation, you want to avoid adding diammonium phosphate (DAP) or complex nutrient additions that contain DAP (g., Fermaid K) when hydrating your yeast. Use hydration-specific products like GoFerm or Nutriferm Energy.
- Most suppliers recommend making 2 additional nitrogen supplementation additions during primary fermentation and after inoculation. If only making 1 nutrient addition after inoculation is practical for you, add your nitrogen supplement at about 1/3 of the way through primary fermentation (e., 1/3 drop in sugar depletion).
A Review: Why to not add DAP at yeast hydration/inoculation
YAN is composed of inorganic (ammonium ion) and organic (primary amino acid) nitrogen components. Amino acids are brought into the yeast cell through transport across the cell membrane. The presence of alcohol and ammonium ions (i.e., DAP) inhibit amino acids from being brought into the cell. This is why winemakers are advised NOT to add DAP at inoculation or at the beginning of fermentation, as yeast can actively absorb organic nitrogen in the juice (aqueous) environment.
Once alcohol concentrations begin to increase, as a result of primary fermentation progression, transport of amino acids from the wine into the yeast cell will be inhibited. Therefore, the primary source of nitrogen will then come from inorganic sources, such as DAP. A more thorough summary of how nitrogen is utilized by yeast can be found at the following pages:
- Wine Made Easy Nutrient Management Fact Sheet
- Cornell University’s FAQs Associated with YAN
- YAN Data Review Over 6 Vintages
- Variations in YAN in the same vineyard sites across multiple vintage years
In general, winemakers can select from three different kinds of nitrogen-based products to add during fermentation:
- Hydration Nutrients (g., GoFerm, Nutriferm Arom, etc.)
- Complex Nutrients (g., Fermaid K, Nutiferm Advance, Superfood, etc.)
- Diammonium Phosphate or DAP
Need more direction on when to add which nutrients? Look no further! We have a practical fact sheet waiting for you at the Penn State Extension website. As a general rule of thumb, remember to make your YAN additions based on the volume of wine that you are treating. For whites, roses, and some reds (e.g., hot pressed Concords), YAN additions will be made based on the juice volume. For most other reds, YAN additions should be based on the must volume.
Dealing with Low YAN Fermentations
Low YAN fermentations are defined as having less than 125 mg N/L in the must/juice at the start of fermentation. In these situations, it’s essential for the winemaker to provide enough “food” for all of the yeast during primary fermentation.
Depending on the reference, most scientific literature will recommend adding up to 200 – 250 mg N/L. This concentration of nitrogen should provide adequate supplementation for the entire biomass throughout the duration of fermentation.
Be aware that if you are using a HIGH NITROGEN DEMANDING YEAST strain (e.g., BM45, ICV-GRE, among others), however, you may be required to add additional supplementation. If you are starting with a low YAN situation and would like to use a high nitrogen requiring yeast strain, we recommend contacting your supplier for specific nutrient addition instructions.
Dealing with High YAN Fermentations
Many suppliers define a high YAN fermentation anywhere above 250 mg N/L. However, some YANs from Pennsylvania grown grapes are at concentrations greater than 400 mg N/L! This YAN concentration can create a challenging fermentation and processing situation for the winemaker.
Due to the excess amount of available nutrients in these situations, yeast can grow and reproduce quickly, which often leads to very rapid and hot fermentations. The speed and temperature of fermentation can affect the aromatics and quality of the wine (i.e., fast fermentations often lead to simpler aroma and flavor profiles). This may not be an issue with some fermentations, but for many white, rosé, or fruit (other than grapes)-based fermentations, aromatic retention should be a priority by the winemaker.
Higher concentrations of the inorganic component of YAN can lead to a high initial biomass of yeast. This is a problem because the rapid increase in yeast populations can lead to starvation by the majority of the yeast by mid- to late-fermentation, especially if there is not enough nutrition to fulfill all of the yeast during fermentation. Yeast starvation leads to yeast stress, and one of the stress responses by yeast is the production and release of hydrogen sulfide. Therefore, having a high YAN at the start of fermentation may cause hydrogen sulfide issues in the wine by the time fermentation is complete.
What should you do if you have a high YAN?
- First, always reference your supplier recommendations. Each year, suppliers publish current guidelines for how and when to add various nutrients during fermentation.
- I’ve found it helpful to document trends in high YAN fermentations. For example, if you notice that a variety with a routine high YAN year-to-year, note the years where hydrogen sulfide becomes an issue. Good record keeping during primary fermentation can remind you what you did during production. You may need to alter these practices for the following vintage year.
- If all else fails, refer to Penn State’s Wine Made Easy Fact Sheet on Nutrient Supplementation during Primary Fermentation
Additionally, high YAN concentrations may leave some nitrogen left over by the end of fermentation and could remain in suspension in the finished wine. This excess “food” could be available for other microorganisms (like acetic acid bacteria or Brettanomyces), which could potentially lead to spoilage problems if the wine is not properly stabilized. In high YAN situations, it is especially important to ensure that the wine is stabilized with adequate sulfur dioxide additions and by minimizing other risk factors (e.g., temperature control of the wine).
It is also be researched that high starting YAN values may led to increased concentrations of ethyl carbamate. Ethyl carbamate is naturally produced by fermentation, but it is a mild carcinogenic compound. For this reason, many countries have legal maximum ethyl carbamate concentrations in wine. For more information on ethyl carbamate, please see this guide published by UC Davis or this Extension report from Virginia Tech’s Enology Grape Chemistry Group.
Our Understanding of YAN is still Developing
Every year, YAN is a big topic of conversation amongst industry suppliers and academics. Current investigations include:
- The impact of primary amino acid uptake as a function of temperature, reported by Cornell University and discussed at the 2016 American Society of Enology and Viticulture (ASEV) – Eastern Section conference (Missouri) in a presentation by Scott Labs.
- YAN recommendations for hybrid varieties produced in the Mid-Atlantic, a topic discussed by Dr. Amanda Stewart from Virginia Tech University during the 2014 PA Wine Marketing & Research Board Symposium. This includes looking at other nutritional factors beyond nitrogen supplementation, which was also discussed at the ASEV-Eastern Conference in 2016 by Scott Labs.
- Optimal nutritional strategies for challenging fermentations, which is often reported in supplier catalogs like the Scott Labs 2016 Handbook
By: Denise M. Gardner
Last week, Dr. Michela Centinari dived into the discussion regarding the role of potassium in the vineyard. While the issue is quite challenging to address in an established vineyard, processing grapes from high pH fruit, or fruit that has the potential to create a high pH wine (>3.70), as a result of high potassium (K or K+) concentrations is also a challenge for the winemaker.
Concentrations of 22 – 32 mmol/L K+ (860 – 1,279 mg/L K+) are considered “normal” ranges for wine grapes (Somers 1977, cited by Mpelasoka et al. 2003), while ranges in the 27 – 71 mmol/L K+ (1,056 – 2,776 mg/L K+) are considered “high” (Somers 1975, cited by Mpelasoka et al. 2003) and may lead to potential winemaking problems. Grapes and juice that come in with high levels of potassium can lead to a series of difficulties for winemakers including:
- High potassium concentrations can cause large increases in pH during primary and malolactic fermentations, which drive the finished wine into a high pH (>3.70) range.
- Color hue, intensity, and stability of red wines can be negatively affected.
- High pH wines produced throughout the Mid-Atlantic may lead to negative perceptions associated with taste and mouthfeel of both white and red wines.
- As pH is a big driver in wine stability, higher pH’s will have impacts on the microbial stability (both in terms of microflora and inhibition of growth), sulfur dioxide levels and efficacy, color stability of red and rosé wines, stability of tartaric acid, and protein stability.
- Higher pH’s leads to an increase in oxidative potential, which may cause premature oxidation for young wines.
Although the articles listed below are not peer reviewed, previous attention has been given to high potassium winemaking issues. Some of the content relayed in these 2 articles will not be discussed in this blog post:
- Really, really high pH remedies from Wines & Vines: a discussion on potassium concentrations increasing the pH of wine and utilization of ion exchange if the problem is not prevented
- High pH and high potassium wines produced in Colorado from White Hall Vineyards: Includes a discussion pertaining to malic acid concentration in high pH fruit. (Author’s note: This article discusses adding tartaric acid prior to fermentation, but not exceeding a TA of 8.0 g/L while hitting a pH of 3.60, ideally. While the practice of analytically checking your additions is encouraged, and will be discussed throughout the duration of this blog post, please note that sampling procedures and tartaric acid settling time will greatly influence your juice TA after tartaric acid addition.)
A problem for winemakers is that unless potassium uptake and management is addressed in the vineyard, they will likely have to deal with having high potassium-based fruit for several years. However, winemakers are encouraged to work with their growers, as this is a relatively newer viticultural issue that the Mid-Atlantic is facing, and it may take several years to stabilize before results are seen in incoming fruit from the vineyard.
In regions like Australia, which frequently experience high K concentrations in their fruit and wines, making tartaric acid additions to the juice, pre-fermentation is often recommended to lower the pH of the must/juice and precipitate some of the potassium as it binds to tartaric acid during primary fermentation. While a 2 g/L of tartaric acid addition to must/juice is a common recommendation for acidulating musts, it may not be enough in order to alter the effects of high potassium concentrations in the fruit. In these cases, a higher addition rate of tartaric acid, such as 4 – 6 g/L of tartaric acid, may not be out of the question.
It should be noted that must/juice acidification will have chemical and sensory implications to the finished wine. If the winemaker is aiming to produce a specific style, making large tartaric acid additions pre-fermentation may not be conducive with the desired and finished wine style. However, when dealing with high potassium issues, and hence, high pH issues, larger tartaric acid additions pre-fermentation seem to be helpful in stabilizing red wine color and improving the flavor of red wines. For those that would prefer a lower TA (<6.0 g/L tartaric acid), deacidification following malolactic fermentation of red wines is recommended. While there are limitations on deacidification practices, including the degree to which a winemaker can deacidify, this action may help improve mouthfeel and decrease the perception of acidity (sourness) in the finished wine.
Wine Trials at PSU
During the 2015 harvest, our research team confirmed that a couple of our varieties that annually had high pH problems came from sites or locations with high potassium retention in the fruit. This did not necessarily correlate with high potassium concentrations in the soil.
From our Biglerville (Adams County) research vineyard, our Merlot contained 1,682 mg/L K+ and Cabernet Sauvignon contained 1,668 mg/L K+ in the 2015 growing season. Both samples were taken from the must and analyzed by atomic absorption analysis at Enartis USA – Vinquiry.
Based on previous research from Somers (1975), both musts were considered high in potassium. The following (Tables 1 and 2) show additional harvest parameters for our Merlot and Cabernet Sauvignon musts in the 2015 season.
As previous yeast strain selection, malolactic bacteria selection, and standard (2 g/L) tartaric acid addition trials did not seem to improve color stability or flavor of the wines in past harvest years, we took the approach at comparing 3 different tartaric acid addition rates (2 g/L, 4 g/L, and 6 g/L) to the Merlot pre-fermentation and two rates (4 g/L and 5 g/L) of tartaric acid to the Cabernet Sauvignon based on previous recommendations made in the Australian literature. There were fewer treatments on the Cabernet Sauvignon due to decreased yields in 2015. Please note that these treatments were not replicated and, therefore, we have not provided any statistical parameters.
For the Merlot, the 2 g/L addition rate of tartaric acid acted as the “control,” as previous years indicated no differences in pH or TA by the end of MLF between wines fermented without tartaric acid added pre-fermentation and a 2 g/L addition treatment. There was no designated “control” for the Cabernet Sauvignon fermentations.
Table 1: 2015 Pennsylvania Merlot must chemistries in 2015; pH and titratable acidity (TA) were adjusted pre-fermentation (i.e., pre-inoculation) and given at least 3 hours of settling time before inoculation with ICV-GRE yeast
Table 2: 2015 Pennsylvania Cabernet Sauvignon must chemistries in 2015; pH and titratable acidity (TA) were adjusted pre-fermentation (i.e., pre-inoculation) and given at least 3 hours of settling time before inoculation with ICV-GRE yeast
The following table (Table 3) shows the differences in pH and TA for each pre-fermentation tartaric acid addition treatment following primary fermentation and MLF for our Merlot wines in the 2015 vintage year.
Table 3: 2015 Merlot wine chemistries (pH, TA, volatile acidity, and alcohol concentration) post-primary fermentation and post-MLF (fermentation trials were not conducted in replicate)
Trends were similar in the 2015 Cabernet Sauvignon wines, as shown in Table 4.
Table 4: 2015 Cabernet Sauvignon wine chemistries (pH, TA, volatile acidity, and alcohol concentration) post-primary fermentation and post-MLF (fermentation trials were not conducted in replicate)
While we do not quite have an explanation for the rise in TA from post-primary fermentation to post-MLF in the 5 g/L tartaric acid addition treatment in the Cabernet Sauvignon wine, we did note that post-bottling, most of the TA’s slightly decreased across all treatments in both Merlot and Cabernet Sauvignon wines. A decrease in TA would reduce the perception of sourness even further. This decrease was likely due to better removal of dissolved carbon dioxide within the wines due to the fact the wines had been moved (i.e., racked, transferred and bottled) more routinely prior to bottling.
The treatments within a varietal were also different sensorially, although this was not quantified. For example, in the Merlot, the first difference noted was the color. The Merlot wine that had been treated with 6 g/L tartaric acid had the most vibrant and red-hued color. The Merlot with a 2 g/L tartaric acid addition had a stronger purple-blue hue. We did not quantify these differences analytically. In terms of taste, the 6 g/L tartaric acid treatment had more noticeable and perceptible sourness, but many that tasted the wine agreed that it could be manipulated with some deacidification trials. The 2 g/L tartaric acid addition treatment tasted flat, had burnt rubber-like flavors and was relatively unappealing. It did not represent a typical flavor profile associated with Merlot. The 4 g/L and 6 g/L tartaric acid addition treatments had more noticeable red fruit flavors and less earthy characters.
What should you do in the winery if you think you have high pH wines as a result of high potassium concentrations in your grapes?
- Find out if potassium concentrations may be a culprit. Now is the time to find out what you are dealing with. In last week’s blog post, Michela recommended getting petiole samples to determine vine nutrition. However, you can also test the fruit (must, juice) and the wine for potassium concentrations as well. We recommend sending your samples to an ISO accredited lab to confirm potassium concentrations in those wines that you believe may be suspect.
- Make tartaric acid additions pre-fermentation (pre-inoculation). With very high potassium concentrations, a 4 – 6 g/L addition of tartaric acid pre-fermentation may not be a detriment to wine quality. However, it is best to know the concentration of potassium you are dealing with before adding up to 6 g/L of tartaric acid pre-fermentation as this can have obvious effects on the wine’s taste and flavor as a finished wine (i.e., make the wine thin or overly sour).
- If you are unwilling to test to the potassium concentration, but have a wine with frequent high pH problems during production, use a 4 g/L tartaric acid addition pre-fermentation instead of 2 g/L. The 4 g/L tartaric acid addition rate is a relative “good guess” zone. Depending on the potassium concentration in your wine, this will either work or it will not work. If you refer to Tables 3 and 4, we can see that the 4 g/L addition rate was not a bad choice for the Merlot as it resulted in an ideal pH (3.63) and a workable TA (5.96 g/L), but for the Cabernet Sauvignon, the wine resulted in a high pH (>3.70) and a high TA (>6.00 g/L). This high pH, high TA situation can make the wine both difficult to manage for stability reasons (e.g., making applicable sulfur dioxide additions) while retaining a relatively sour taste.
- White wines can also suffer from high potassium. While the content of this blog post has focused on red wines and the effects of color stability and flavor associated with higher pH’s and high potassium concentrations, white wines can also be affected by high potassium concentrations. In most instances, high potassium can relate to a high pH in the finished wine, which makes the white wine difficult to stabilize or add proper sulfur dioxide additions in order to minimize microbial risk. Also, many of these wines have low TA’s, giving the white wine a fat, round, or flat mouthfeel (dependent on the variety). Stylistically, this may not be undesirable, but it is a sensory component that winemakers should be aware of that may occur in these chemical situations.
- Alter your pH and sourness post-malolactic fermentation. If the wine tastes too sour for your preference, the time to de-acidify is post-MLF with these wines. By that time, the color pigments will be fully extracted from the red skins and the flavors will be as optimal as they can be for the variety. For our Merlot wines, we made additions using (ironically) potassium carbonate, but calcium carbonate can also be used to de-acidify wines. I usually recommend Patrick Iland’s book for practical information on how to make de-acidification trials in wine. WSU also provides appropriate options and instructions for deacidifying wine.
Mpelasoka, B.S., D.P. Schachtman, M.T. Treeby, and M.R. Thomas. (2003) A review of potassium nutrition in grapevines with special emphasis on berry accumulation. Australian Journal of Grape and Wine Research. 9:154-168.
Somers, T.C. (1975) In search of quality for red wines. Food Technology in Australia. 27:49-56.
Somers, T.C. (1977) A connection between potassium levels in the harvest and relative quality in Australian red wines. Australian Wine, Brewing and Spirit Review. 24:32-34.
By Michela Centinari
Potassium (K) plays a critical role in many plant physiology and biochemistry processes (e.g., photosynthesis, osmoregulation, enzyme activation, etc.). Inadequate supply of K can result in reduced shoot, root and fruit growth as a result of reduced xylem sap flow, and can also increase the risk of drought stress . Potassium deficiency leads to inhibition of photosynthesis and to sugar (sucrose) being “trapped” in the leaves which adversely affects yield, fruit ripening and berry soluble solid concentration .
While grape growers should monitor vine health to avoid K deficiency, at the same time they should also be on the lookout for excessive concentration of K in vine tissues (e.g., leaf, berry) because of its potential negative impact on vine health and wine quality.
When looking back at the past two years of inquires received from Pennsylvania wine grape growers related to vine nutrient or nutrient-related problems, we (Denise and I) found that the number of those concerning excessive concentration of K and related issues (e.g., high/unstable wine pH) were more common than inquiries related to K deficiency, which mostly occurred in young vineyards.
This short article will review problems related to high/luxury absorption of potassium, briefly discuss how soil mineralogy and pH can affect K uptake, why it is important to regularly monitor vine nutrient status, and what environmental and cultural factors may impact K uptake and accumulation in plant tissues. In-depth information on mode of uptake and transport of K in the plant, and functions of K can be found in “A review of potassium nutrition in grapevines with special emphasis on berry accumulation” by Mplelasoka et al. 2003 .
Also, you can refer (as I did) to the valuable web-resources recently published by Virginia Tech University (Dr. Tony Wolf and Russel Moss), which includes edited information to supplement Chapter 8 of The Wine Grape Production Guide of Eastern North America:
Potassium in Viticulture and Enology, May 2016
Why high/excessive concentration of K in the grape berries may negatively impact wine quality?
Grape berries are a strong sink for K during ripening. Potassium accumulates mainly in the berry skin tissues (Figure 1) and is the most abundant cation (K+, hereafter referred to as K) in grape juice . Mature grapes may have, indeed, almost twice as much K as nitrogen ; for example one ton of mature grapes contains about 11 lbs (5 kg) of K .High concentration of K in grape juice (e.g., > 50 mmol/L) may result in a high juice pH (e.g., > 3.8) and negatively impact wine quality . During winemaking, high concentration of K causes precipitation of free acids, mainly tartaric acid, leading to an increased wine pH . The high pH may reduce color stability of red wines due to a shift of anthocyanins to the non-colored forms . High concentration of K may also reduce respiration and the rate of degradation of malic acid and consequently increase malolactic fermentation .
While many studies linked high juice/wine pH to high juice/wine K concentrations (see for example Figure 2) it is also true the other factors, aside from K, can affect wine pH and that wines with low pH (e.g., < 3.25) may also have high K concentration . Moreover, there are varietal differences in the relationship between juice pH and K concentration (see Chardonnay vs. Shiraz, Figure 2), as well as between wine K and juice K .pH can be adjusted during winemaking through addition of tartaric acid, adding additional costs for the wineries. Ensuring adequate concentration of K in the grapes at harvest will not only help reduce winemaking costs but is also likely to improve wine quality .
In next week’s blog post, Denise Gardner will discuss options for dealing with high K concentrations in juice and wine. However, the first step is to determine if there is or there may be a potential problem with K in your vineyard (either deficiency or excess level).
Potassium availability in the soil
It is well known that concentration and availability of K vary with soil type and is greatly affected by the physical and chemical properties of the soil . Potassium in soil is classified into four groups in relation to its availability to the plants: 1) water-soluble (K dissolved in soil solution), 2) exchangeable (on cation exchange sites of surfaces of clay minerals and humic substances), 3) non-exchangeable and 4) structural forms .
The water-soluble and exchangeable pools (1 & 2) represent only » 0.1-0.2% and 1-2% of the total soil K, respectively . Both forms are readily available for plant root absorption. The majority of the K is bound in mineral structures, such as mica and feldspar, or it is part of secondary minerals such as vermiculite  and thus considered a (very) slowly-available source of K for plants. Clays also have different capabilities of binding K as well as different rates of K release . For example, micas release K at a remarkably faster rate than feldspar .
Since clay mineralogy impacts the release of K into the soil solution over time and the K supplying power of the soil, it is important to have detailed information concerning the soil structure and composition of your vineyard (i.e., does your site have high levels of exchangeable K?).
Other important factors affecting K availability are soil pH and relative concentration of K to that of the other cations, such as magnesium (Mg2+) and calcium (Ca2+). Low/acidic soil pH (<6) increase K availability and potentially increase its uptake while reducing uptake of Ca2+ and Mg2+ . Excess K can decrease concentrations of Ca2+ and Mg2+ in plant tissues and induce symptoms of Mg deficiency  (Figure 3).
Assessing K concentration in the vine
Conducting plant tissue (petiole) testing on a regular basis (annual or every two years) to monitor vine nutritional health (K and other essential nutrients) and promptly correcting problems related to nutrient imbalance is strongly recommended. Visual observations of foliar symptoms of nutrient deficiency or toxicity are important clues (Figure 4), but a nutrient management program should not be exclusively based on visual observations because: 1) it is possible to be misled by symptoms that are not nutrient related (e.g. mite injury, virus, etc.) and 2) to develop an appropriate nutrient management program it is crucial to understand the nutritional requirements of the vines .
Soil testing is an extremely useful tool in the pre-planting stage for determining the potential of a vineyard site and the amendments needed, and also for monitoring soil pH over the years (after the vines are planted). However, soil testing only tells one side of the story: what is potentially available to the vine. Again, the recommended and preferred method to assess vine nutritional health and to effectively identify potential nutrient (in this specific case K) deficiency or excess is plant tissues (petiole) testing.
Some limitations of the soil testing include:
- Soil samples are often limited to the first 10-20 inches. Roots of mature vines tend to be sparse and, in deep soils, they can grow much deeper than 10-20 inches. Thus soil testing may not be a good indicator of the soil/plant interaction.
- Soil testing may underestimate the reservoir of K available to the vines . The laboratory nutrient extraction analysis is run over minutes while vines have much longer to absorb/extract nutrients [6,9].
Thus, don’t be too surprised if results of K soil testing are poorly correlated with those of plant tissue testing [6,7,9].
When is the best time to conduct leaf petiole testing?
The preferred time for leaf petiole testing is bloom and late-summer (70 to 100 days after bloom). Assuming bloom was in June, you may still have time left this season to conduct the test. In case of suspected K or other nutrient deficiency the samples can be collected anytime during the season . It is important to have a standardized tissue-sampling procedure. For example, at bloom collect 60 to 100 petioles of healthy leaves opposite to the flower cluster (first or second) for each cultivar. Don’t collect more than one or two petioles per vine. Late summer samples should be collected from “the youngest fully expanded leaves of well-exposed shoots, usually located from 5 to 7 leaves back from the shoot tip”. If the shoot has been hedged, collect “primary leaves near the point of hedging” .
More information on how to collect leaf petiole samples and interpret the results can be found at Monitoring Grapevine Nutrition (eXtension.org) and in the Wine Grape Production Guide for Eastern North America, chapter 8 .
Reference values of K concentration in grape leaf petioles for bloom- and late summer-collected samples are reported in Table 1. (Note: the source used is the Wine Grape Production Guide for Eastern North America , sources from other regions may provide slightly different standards).
Table 1. Reference values for K concentration in grape leaf petioles for bloom- and late summer-collected samples.
In table 2, I included the results of a petiole test conducted at a research vineyard in south central Pennsylvania. At bloom, K concentrations in the leaf petiole of Cabernet Sauvignon and Merlot vines were slightly above the ‘excessive’ range. We repeated the analysis around veraison and found that at that time K concentrations were greatly above the 2% ‘excessive’ threshold. Not too surprisingly, at harvest, both varieties had high grape juice pH and high K concentration according to reference values reported by Mpelasoka et al. 2003  (Table2). Soil testing showed a high level of exchangeable K, and low pH (below 6), the vines were highly vigorous: all factors that can contribute to luxury uptake of K.
Table 2. Potassium concentrations in the petiole of Cabernet Sauvignon and Merlot leaves at bloom and veraison. Potassium concentration and pH of the grape juice was measured at harvest.
What to do next?
In case of K deficiency (petiole and soil testing and visual observations) (Figure 4) you can consult with an extension educator in your county or a viticulture consultant who can assist with the development of an appropriate fertilization program.
For those of you who may have missed it, Tony Wolf (professor and viticulture extension specialist at Virginia Tech university) recently issued an important update on K fertilization recommendations . The lower limit of optimal soil K reported in the “Wine Grape Production Guide for Eastern North America”  has changed from 75 ppm (150 lbs/ac) to 40 ppm (80 lb/acre) (Note: those values are based on Mehilch-3 extraction protocol which is the one used by Penn State Agricultural Analytical Services Lab but not by Virginia Tech). In the July issue of Viticulture Notes Tony Wolf wrote:
“Potassium fertilizer is not recommended pre-plant or to existing Virginia vineyards if the soil test results are at or above 40 ppm (80 lbs/acre) actual K as determined by Mehlich-3 test procedures, or 28 ppm (56 lbs/acre) actual K as determined by Mehlich-1 test procedures. However, young vines should be visually monitored and irrigated under drought conditions to avoid potential K deficiency on soils that are inherently low in exchangeable K.”
How can K concentration and uptake by the vines be reduced?
In the pre planting stage, if the soil selected for planting the vineyard has high exchangeable K levels, an option is to select rootstocks that accumulate low concentration of K. Rootstocks, and grapevine varieties in general, differ in their capacity of K uptake and translocation . For example, rootstocks with V. berlandieri genetic background tend to have reduced K uptake as compared to others, as those with V.champini parentage . In northern California, Chardonnay, Cabernet Sauvignon and Zinfandel vines grafted on 101-14 Mgt and 3309C (V. riparia x V. rupestris), two commonly-used rootstocks in the eastern US, consistently had leaf petiole K concentrations within the intermediate range compared to those of the same varieties grafted on V. berlandieri (lowest K concentrations) and V. champinii (highest K concentrations) crosses . A study conducted at Winchester, VA, by Tony Wolf research group found that the use of 420-A (V. berlandieri x V. riparia) rootstock reduced juice pH in Cab Sauvignon vines as compared to those grafted on 101-14 Mgt and Riparia .
However, it is important to consider that the performance of rootstocks in terms of K uptake varies depending on rootstock-scion combination (i.e., the same rootstock may have variable effects on different scion varieties), soil type, climate, and management practices.
Another aspect to consider when selecting rootstocks is their vigor or growth-potential. Vigorous rootstocks or rootstocks that convey high vegetative growth and yield potential to the scion may cause increased K uptake as a result of increasing vine demand.
Growth drives K uptake: Factors such as high vine vigor, leaf area, and extensive root system can enhance K uptake, translocation, and accumulation in the grape berries. Soil moisture increases the dissolution of K from clay particles, thus facilitates K supply and uptake by the roots. High soil water availability also leads to increase vegetative growth which may indirectly affect K uptake and its accumulation in the berries.
Shaded leaves are a source of K translocation to the grape berries: Canopy microclimate and mainly foliage shading can affect the accumulation of K in the berries. For example, artificial (shading cloths)  or natural (canopy) shading  was found to increase K concentration in berries and juice. We don’t know exactly why this happens yet, but it is possible that in conditions of low sugar accumulation, as under foliage shading, the increasing accumulation of K in the berries helps regulating osmotic potential, maintaining cell turgor and thus minimizing reduction in berry growth which may occur with low sugar content .
Can crop load be regulated to reduce K accumulation in the fruit?
Since berries after veraison are the primary sink for K, we would expect that regulation of crop load (commonly defined as the ratio of fruit weight to pruning weight or to leaf area) can affect K translocation and accumulation in the berries . However, results from previous studies are inconclusive. For example, in hot climate regions (Israel, California) cluster thinning reduced berry K in one study  while having no effect on juice K in another study . Factors such as grape variety, timing of thinning, and the amount of crop retained can greatly affect outcomes and explain why the effect of crop load on accumulation of K in the berries still remains unclear. Making matters more complicated, manipulation of crop load may also affect vegetative growth, and the degree of foliage shading, thus indirectly impacting K translocation into the berries.
Generally speaking, over cropping may result in a lower or insufficient amount of K in the vine tissues (K deficiency tends to be more pronounced on heavily cropped vines after veraison). At the same time if yield is very (too) low the shoots may become competitive sinks for K and as a result its accumulation in the berries may be reduced .
Vineyard management practices that decrease leaf shading may reduce K accumulation in the berries. Reducing canopy density and shading, either through a) the removal of lateral shoots, b) lateral and top-hedging, or c) basal leaf removal reduced K concentration and, in some cases, pH in juice and wine of Tannat vines in Uruguay (Figure 5) . The use of divided-trellis systems could also be a method to manage highly vigorous vines and decrease leaf shading .
In conclusion, if you suspect a problem with high vine K and/or high juice/wine pH, here a few things you can do:
- Plant tissue (petiole) analysis to assess the K level of your vines and to confirm that high/excessive K is the real issue. Again, don’t rely exclusively on soil testing, which is still useful to assess soil pH and other factors that may affect K uptake.
- If your vines are highly vegetative you could test the effect of reducing foliage shading on juice/wine pH and K. Reducing canopy density may also have additional benefits for the health of the grapes and quality. Canopy practices such as basal leaf removal, hedging, shoot positioning and thinning can be used. It is a good practice to leave a block of untreated vines (no additional canopy management) as a control. At harvest measure juice pH and K concentration in the treated (less shaded) and untreated (more shaded) vines to assess if the extra canopy management mitigate the K/pH level in the grape juice.
If you have tried or panning on trying to manage K levels in your vineyards we would be happy to hear about your experience and methods/results.
- Keller M. 2010. The Science of Grapevines: Anatomy and Physiology. Publisher: Academic Press.
- Mpelasoka BS, Schachtman BP, Treeby MT, Thomas MR. 2003. A review of potassium nutrition in grapevines with special emphasis on berry accumulation. Aust. J. Grape Wine Res. 9, 154–168.
- Coombe BG, Dry PR. 1992. Viticulture Volume 2 – Practices. Publisher: Winetitles.
- Walker RR, Clingeleffer PR, Kerridge GH, Rühl EH, Nicholas PR, Blackmore DH. 1998. Effects of the rootstock Ramsey (Vitis champini) on ion and organic acid composition of grapes and wine, and on wine spectral characteristics. J. Grape Wine Res. 4, 100–110.
- Kodur 2011. Effects of juice pH and potassium on juice and wine quality, and regulation of potassium in grapevines through rootstocks (Vitis): a short review. Vitis 50, 1–
- Wolf TK. Viticulture Notes. Vol 31 No. 5. 23 July 2016. Virginia Tech University Cooperative Extension. Available at: http://www.arec.vaes.vt.edu/alson-h-smith/grapes/viticulture/extension/news/vit-notes-2016/vit_notes_july_2016.pdf
- Walker RR, Blackmore DH. 2012. Potassium concentration and pH inter-relationships in grape juice and wine of Chardonnay and Shiraz from a range of rootstocks in different environments. J. Grape Wine Res. 18, 183–193.
- Zörb C, Senbayram M, Peiter E. 2014. Potassium in agriculture – Status and perspectives. J. Plant Physiol. 171, 656–669.
- Beasley, E, Morton L, Ambers C. 2015. The role of soil mineralogy in potassium uptake by wine grapes. Progress report to the Virginia Wine Board http://www.vawine.org/wpcontent/uploads/2015/11/REPORT-2-Beasley-Final-Report-SEPT-2015-2.pdf
- Moss R. 2016. Potassium in viticulture and enology. Virginia Tech University Cooperative Extension. Available at: http://www.arec.vaes.vt.edu/alson-h-smith/grapes/viticulture/extension/news/vit-notes-2016/kinvitandeno.pdf
- Wolf TK. 2008. Wine grape production guide for Eastern North America. Natural Resource, Agriculture, and Engineering Service: Ithaca, NY USA.
- Wolpert JA, Smart DR, Anderson M. 2005. Lower petiole potassium concentration at bloom in rootstocks with Vitis berlandieri genetic backgrounds. Am. J. Enol. Vitic. 56:163-169.
- Rojas-Lara BA, Morrison JC. 1989. Differential effects of shading fruit or foliage on the development and composition of grape berries. Vitis 28, 199–208.
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- Hepner Y, Bravdo B. 1985. Effect of crop level and drip irrigation scheduling on the potassium status of Cabernet Sauvignon and Carignane vines and its must and wine composition and quality. J.Enol. Vitic. 36, 140–147.
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By: Bryan Hed
We’re in the final leg of the season and it’s time to size up our remaining challenges through the ripening period. Fruit are no longer susceptible to many of the major diseases like powdery and downy mildew and black rot that can cause crop loss during earlier stages of berry development. But for some grape varieties, particularly wine grapes that produce compact clusters, there is another major hurdle to work through to harvest; late season bunch/sour rot. I am referring to the rotting of fruit in clusters that occurs during the later stages of the ripening period, just a few heartbreaking days or weeks before harvest. Bunch rot can involve the colonization of fruit by a number of different microorganisms, both fungi and bacteria. But the main culprit in most regions of the Northeastern U.S. is the fungus, Botrytis cinerea (Figure 1). Fortunately, we have a number of chemical control options that are quite effective against this fungus that I have listed below. I have organized them according to the FRAC (Fungicide Resistance Action Committee) group that each product belongs to. Basically FRAC groups are fungicide chemistries with the same or similar mode of action, so that pathogen resistance to one fungicide is going to confer cross resistance to another, within that same FRAC group. For example, notice that Vangard and Scala are in the same FRAC group; 9. This means that if a population of Botrytis in a vineyard has developed resistance to the active ingredient in Vangard, then it will also be resistant to the active ingredient in Scala, even though the active ingredients may be different (cyprodinil in Vangard and pyrimethanil in Scala). The mode of action (the way in which the fungicide disrupts a specific metabolic pathway in the fungus, killing it) of these two chemistries is the same, or similar enough that pathogen resistance to one chemistry will confer resistance to the other.
- FRAC group 2: Rovral, 7 day pre-harvest interval
- FRAC group 7: Endura, 14 day pre-harvest interval
- FRAC group 7 (and 3, which is not for Botrytis): Luna Experience, 14 day pre-harvest interval
- FRAC group 7 and 11: Pristine, 14 day pre-harvest interval
- FRAC group 9: Vangard, Scala, 7 day pre-harvest interval
- FRAC group 9 (and 3, which is not for Botrytis): Inspire Super, 14 day pre-harvest interval
- FRAC group 9 and 12: Switch, 7 day pre-harvest interval
- FRAC group 11: Flint, 14 day pre-harvest interval
- FRAC group 17: Elevate, 0 day pre-harvest interval
No doubt many wine grape growers have already applied a bloom, pre-bunch closure, and veraison spray to bunch rot susceptible varieties. However, one or more applications may be necessary in some vineyards. Populations of the Botrytis fungus are quite adept at developing resistance to these fungicides; be mindful to rotate FRAC groups and limit the application of any one FRAC group to one or two per season to delay the development of that resistance. If you have to use a FRAC group more than once per season, it would be better to compose one of those two applications with a material that contains a second FRAC group for Botrytis. For example, if you already used Scala, it would probably be better to apply Switch (after you’ve already rotated to FRAC group 2, 7, 11, or 17) than to apply Vangard or another Scala spray. Most of these materials are considered ‘high risk’ for resistance, so rotation is extremely important to maintaining the effectiveness of these products. Also, pay attention to pre-harvest intervals which range from 0 to 14 days. That said, you can’t spray your way completely out of the damage that Botrytis and other microorganisms can cause; consistently effective bunch rot control programs must be integrated with a generous dose of cultural practices like fruit zone leaf removal, sanitation, canopy management, and vine balance. And, unfortunately, these chemistries listed above are specific for Botrytis and will not control many of the other microorganisms that may make up the bunch rot complex or that lead to the dreaded sour rot complex.
I’ve already alluded to one of the major predisposing factors for bunch rot (including sour rot) in grape clusters, and that is cluster compactness. The compactness of clusters is responsible not only for initiating much of the fruit rot that occurs in clusters, but perhaps more importantly, for the rapid spread of rots throughout the cluster (Figure 2). Rots can be initiated in loose grape clusters as well (by bird or insect damage, for example), but generally do not spread beyond the damaged berry or berries. However, in compact clusters, a single damaged berry can spread rot to large sections of the cluster by virtue of the close contact between those berries. Contact between berries in compact clusters also reduces cuticle thickness, an important barrier to rot pathogens, and reduces pesticide penetration into clusters for protection of berry surfaces against Botrytis and damage by insects. Cluster compactness also increases the effects of retained bloom trash (dead flower parts) inside clusters that can provide a substrate for Botrytis, increasing fruit rot by harvest. Taken together, this generally makes berries in compact clusters much more susceptible to invasion by fruit rot pathogens than berries in loose clusters.
A series of greenhouse experiments we conducted years ago also suggested that latent (dormant) infections of Botrytis can be activated by the kind of berry injury that occurs in compact clusters. Latent Botrytis infections are infections that occur during bloom and the early fruit development period for which you apply that bloom and pre-closure spray. Years ago, we monitored the incidence of latent infections in our block of Vignoles and found that even though the incidence appeared to increase throughout the berry development period, most of these infections did not lead to fruit rot by harvest. In fact, when we inoculated clusters of potted, greenhouse grown Chardonnay vines with Botrytis shortly after bloom, generating high levels of latent infection in berries, the berries did not rot during ripening if they remained intact in the greenhouse, unexposed to weather, birds, insects, or compactness (the clusters were thinned after inoculation and thinned berries were used to determine latent infection levels). However, when we surface sterilized the berries (to eliminate any Botrytis on the outside of berries) and created small injuries at the berry/pedicel interface of ripe berries (the kind of injury that commonly occurs in overcrowded clusters) the vast majority of the inoculated berries quickly rotted compared to berries that were not inoculated with Botrytis (checks).
By loosening clusters, damage from berry overcrowding can be minimized and bunch/sour rot development can be greatly alleviated. Unfortunately, loosening clusters in a consistently effective AND cost effective way is not always an easy thing to accomplish. Over the years we have examined a number of potential methods for cluster loosening with varying levels of success. Treatments such as pre-bloom fruit zone leaf removal have provided the most consistently significant reductions in cluster compactness and fruit rots in most years. The pre-bloom timing of fruit zone leaf removal simply combines the benefits of an open, sun lit fruit zone (which has been well documented by many investigators over the past several decades) with a reduction in cluster compactness and rot susceptibility. In our experiments, this treatment has typically been applied by hand, but the technology exists to mechanically remove leaf tissue around inflorescences (pre-bloom) without serious damage to them, and trials are being conducted to evaluate the mechanization of the pre-bloom leaf removal on a number of grape varieties. So far, results have been mixed depending on variety and trellis training system. In vineyards where we were able to compare pre-bloom mechanized leaf removal with pre-bloom leaf removal by hand and post-bloom mechanized leaf removal, the effects of pre-bloom mechanized leaf removal (increased light exposure of clusters, looser clusters, less rot, yield reduction) generally fell somewhere between the two latter treatments. The hope of this research is to expose growers to some new possibilities for fruit rot control and increase the potential for its adaptation to commercial vineyards and adoption by growers. We’ve examined other technologies with potential for cluster loosening and improved fruit rot control, but unfortunately their adoption is more problematic. For example, we have found that inexpensive gibberellin sprays around bloom have also been effective at loosening clusters and enhancing rot control on Vignoles and Chardonnay with little or no serious negative side effects. But they are currently ‘off label’ and are very unlikely to ever become legal applications in the United States. Also, the effects of gibberellin sprays are variety specific and therefore must be examined and defined for each variety: in our experience, low rates (5-20 ppm) can have serious negative side effects on Vitis vinifera Riesling, whereas rates as high as 100 ppm have had little or no effect on Vitis interspecific hybrid ‘Chancellor’.
More recently, work conducted by Megan Hall, a grad student of Wayne Wilcox at Cornell University, has shown that additional pesticide applications during the latter stages of ripening can significantly reduce the development of sour rot. Her work has shown a close connection between fruit flies and sour rot development; the presence of the flies is important to the accumulation/generation of acetic acid in rotting fruit. Treatments composed of weekly, tank mix applications of an insecticide (to control the flies) and an antimicrobial (to kill bacteria) have been found to reduce sour rots by 50-80% over unsprayed vines. So far, the best results appear to occur when weekly sprays are initiated before sour rot symptoms are observed (preventive sprays before about 15 brix). This exciting work should provide yet another effective option for sour rot control in the wet, humid parts of the eastern U.S. and we are looking forward to hearing more about this rot control option in the near future.
LATE SEASON LEAF DISEASE CONTROL
Beyond the management of bunch rot on susceptible wine varieties, there is also the matter of keeping canopies (leaves) as clean and functional as possible, for as long as possible. Diseases like powdery and downy mildew can continue to be of concern into late summer and early fall, especially for growers of Vitis vinifera. The mildews can greatly reduce leaf function if allowed to spiral out of control. The ability of the canopy to continue to photosynthesize is crucial to the ripening of the crop and canes and the storage of sugars (starch) in trunks, arms, and roots, which relates to winter hardiness. The winters of 2014 and 2015 are harsh reminders of just how important this can be. Allowing grapevines to go into winter dormancy with less than optimal preparation can leave them more susceptible to damage by severe cold and another plague of crown gall to have to deal with for years to come.
Good control of powdery mildew up to about Labor Day can also go a long way to reducing overwintering inoculum and disease pressure the following spring. This finding was the result of some excellent research conducted by Wayne Wilcox, Dave Gadoury and graduate students at Cornell University. When powdery mildew infected leaves die by that first hard frost in fall, the mildew on those leaves stops developing and also dies…unless it has had time to form fully mature, winter resistant resting structures called chasmothecia. If the chasmothecia in a powdery mildew colony do not have time to fully mature before the grape tissue dies (as from infections that were roughly initiated after early September), they will not survive the dormant period (winter) and will not contribute to the bank of primary inoculum that infection periods draw upon the following spring. Knowing this, a grower can get a better handle on the ‘size’ of the powdery mildew problems he/she will potentially face next spring. If, for example, you had heavy mildew development earlier in this season (on clusters and/or leaves), expect to have to deal with powdery mildew early next season and take appropriate action during early shoot growth stages with preventive fungicide sprays. This is particularly important if you are growing Vitis vinifera and much less important for growers of native varieties like Concord and Niagara.
Downy mildew appears to be much less a widespread problem this year. In fact, in our ‘neck of the woods’ along the southern shore of Lake Erie, droughty conditions have prevailed throughout most of the season, and only now are we even beginning to see a few downy mildew infections on leaves close to the ground. At this point in the season regular scouting for this disease is the first line of defense, and in areas that remain relatively dry, perhaps the only control measure needed (?). However, in areas where the disease has remained active throughout the season, be vigilant about keeping it under tight control. Late season epidemics of this disease can quickly strip susceptible wine varieties of their leaves, effectively bringing an early halt to ripening.
For further reading on this and many other disease management topics, refer to the 2016 New York and Pennsylvania Pest Management Guidelines for Grapes. If you don’t have a copy, you can get one through Cornell University press. Every commercial grape production operation should have one!