By Dr. Molly Kelly, Enology Extension Educator, Department of Food Science
As harvest begins you may want to consider utilizing non-Saccharomyces yeast strains. These strains have been shown to improve aromas, lend complexity and improve mouthfeel. In this post, we will provide an overview of their use and provide information concerning commercial strains available.
The Use of non-Saccharomyces Yeast in Winemaking
The use of S. cerevisiae as a starter culture is the most widespread practice in winemaking. There is, however, an interest in conducting uninoculated fermentations. An uninoculated fermentation is often referred to as a “spontaneous” or “native” fermentation involving the sequential action of various non-Saccharomyces and indigenous Saccharomyces yeasts. The use of “mixed starter” of non-Saccharomyces with strains of Saccharomyces cerevisiae provides an alternative to both “spontaneous” as well as inoculated fermentations. The possible benefits include added complexity, enhanced ability to secrete enzymes important in production of aroma compounds and a fuller palate structure.
The ability of non-Saccharomyces yeasts to produce wines with distinct flavor profiles has increased interest in the use of such yeasts in mixed starters. In addition, research demonstrating the ability of non-Saccharomyces yeasts to lower alcohol content of wines, control wine spoilage and improve additional wine properties have been reported.
Grape musts naturally contain a mixture of yeast species and therefore fermentation is not a “single species” fermentation. During crush, the non-Saccharomyces yeasts on the grapes, cellar equipment and in the environment may come in contact with the must. Cellar surfaces play a smaller role than grapes as a source of non-Saccharomyces yeasts.
It is believed that a selected and inoculated strain of S. cerevisiae will suppress any “indigenous” non- Saccharomyces species and dominate the fermentation process. However, several studies have shown that non-Saccharomyces yeasts can persist during fermentations inoculated with pure cultures of S. cerevisiae.
Non-Saccharomyces yeasts are thought to be sensitive to sulfur dioxide (SO2), poor fermenters of grape must and intolerant to ethanol. It is generally accepted that non- Saccharomyces yeasts, not initially inhibited by SO2, would not survive during fermentation due to combined toxicity of SO2 and alcohol. However, research has shown high numbers (106-108 cells/ml) and persistence of non-Saccharomyces yeasts in some wine fermentations, suggesting their potential role in winemaking.
There are two general practices of inoculation when using non-Saccharomyces yeasts in mixed starters. The first, co-inoculation, involves the inoculation of the selected non-Saccharomyces yeasts at high cell concentration along with S. cerevisiae. The second practice, sequential inoculation, allows initial inoculation of selected non-Saccharomycesyeasts at high levels which are allowed to ferment on their own for a given amount of time before S. cerevisiae is added to complete the fermentation. Although both viable, potential interactions between yeast could determine which strategy is more appropriate. Today, there are available many non-Saccharomyces strains compatible with Saccharomyces strains for the improvement of wine primary aroma. See below.
The most frequently studied species include: Torulaspora delbrueckii, Metschnikowia pulcherrima, Candida zemplinina, Hanseniaspora species and Lachancea thermotolerans).
These yeasts are usually poor fermenters, therefore S. cerevisiae (either indigenous or inoculated) is necessary to take the fermentation to completion. Typically, non-Saccharomyces yeasts have been used in sequential fermentation where they grow or ferment prior to inoculation with S. cerevisiae.
Why use non-Saccharomyces yeast?
What do these “native” yeasts have to offer winemakers and how can they be utilized in a planned and controlled manner to produce desired wine styles? Recently, consumer and market demand for lower ethanol wines has driven some research to develop various approaches to produce these wines. Several studies have reported lower ethanol yields when using non-Saccharomyces yeast. In addition, some non-Saccharomyces yeast can utilize sugars with the production of desirable esters and other flavor/aroma compounds with the added advantage of only minimal production of ethanol.
The variety of flavor/aroma compounds produced by different non-Saccharomyces yeasts is well documented. The compounds produced by different Saccharomyces yeasts include: terpenoids, esters, higher alcohols, glycerol, acetaldehyde, acetic acid and succinic acid. Wine color may also be affected by non-Saccharomyces yeast. Conversely, the improper use of non-Saccharomyces yeasts may result in serious fermentation issues including: stuck/sluggish fermentation, high levels of acetic acid and ethyl acetate, as well as lack of reproducibility etc. The goal of the winemaker is to emphasize the positive impact of non-Saccharomyces wine yeasts while minimizing its negative impact.
There are potential benefits of the use of non-Saccharomyces yeast in wine production; the abundance of grape yeast biodiversity presents many opportunities to explore their use. Strain selection is of key importance, as not all strains within a species will necessarily show the same desirable characteristics. The goals of many researchers have included: efficient sugar utilization, enhanced production of volatile esters, enhanced liberation of grape terpenoids to improve wine flavor and other sensory properties. These goals can be met by selected non-Saccharomyces wine yeast and their proper use in the winery.
Please see links below to information summarized by PSU student Tyler Chandross-Cohen on commercial non-Saccharomyces stains.
Please contact me or your Scott labs representative with any questions.
BIODIVA YEAST: This Yeast was initially sold in a pre-blended kit, partnered with a specific S. cerevisiae strain, but now is isolated for winemakers who can match it with a compatible S. cerevisiae of their choosing for both red and white wines. This isolated yeast makes developing wine more customizable. After creating your own blend, the resulting wines will have more intense aromas, mouthfeel and complexity. The S. cerevisiae strains compatible with Biodiva are 43, BDX, ICV D254, L2056, QA23, and VRB.
FLAVIA YEAST: This yeast is a pure culture of Metschnikowia pulcherrima, which is selected for its ability to produce aroma and flavor revealing enzymes. Flavia is best used with creating aromatic whites and rosés. Flavia will enhance the aroma and flavor profiles of wines optimizing varietal characteristics while bringing freshness and volume in the mouth.
By Dr. Helene Hopfer, Assistant Professor of Food Science, Department of Food Science
In late July of 2019, I was fortunate to be able to participate at the 17th AWITC in Adelaide, Australia. I was invited to speak about our sensory regionality study on commercial Riesling and Vidal blanc wines from Pennsylvania.
Last year, Dr. Kathy Kelley wrote about her sabbatical leave in Australia, and provided an excellent overview into Australia’s wine industry, therefore, this blog post will focus on the presentations and posters at the conference.
TheAustralian Wine Industry Technical Conference & Exhibition (AWITC)is happening every three years, organized by The Australian Wine Research Institute (AWRI)and the Australian Society of Viticulture & Oenology (ASVO). Combining plenary sessions, workshops, poster presentations and a large trade exhibition, the AWITC attracts a large audience (over 1,200 participants this year) primarily from the Australian wine industry. Over 4 days, every aspect of grape growing and wine making, from vineyard to grape vine to enology and wine consumers is covered, providing scientific stimulation and lots of discussion for the industry. Intended to present the latest research findings while at the same time being approachable and transferrable for industry members, the AWITC hosts a wide variety of speakers (academics, industry members, governmental speakers, as well as forward-thinking leaders from other industries). Proceedings and video webcasts of all talks will be made available online on the website, where also all past proceedings are made public. Lots of participants also live-tweeted from the conference, so many impressions can also be found on the official event twitter handle @The_AWITC.
The conference started out with a traditional welcome by a local Aboriginal leader from the Adelaide Plains people. Providing a Welcome to his people’s land and an invitation to learn and work collaboratively, his inspiring speech was a great kick-off to the event, followed by the official opening by the Australian Minister for Primary Industries and Regional Development.
In the first two sessions, the supply and demand for Australian wine and its future were evaluated. Following the official outlook from Wine Australia, Warren Randall provided a thought-provoking talk on China very soon becoming the number 1 wine-consuming nation in the world. Although individual wine consumption for Chinese is estimated to reach 1.6 L per person per year (compare to US consumers averaging to 3.1 L per person per year), the sheer number of Chinese middle-class consumers leads to an estimated additional need of 850 million L within the next 5 years. This additional need equates to 1.2 m tones of grape, about 71% of Australians total annual production! The Chinese will remain to be a net importer, particularly for quality wine – the question is though whether Australia will be able to satisfy this demand, especially with the severe drought many Australian grape-growing regions face.
The subsequent talks reiterated the importance of China as a major Australian wine importer as well as for Australian wine tourism: Brent Hill from the South Australian Tourism Commission presented compelling research showing that wine tourism improves brand recall and sales, independent of winery size. For example, international marketing campaigns in combination with direct flights to Adelaide led to tripling visits from China to wineries in South Australia. Wine tourism also aligns nicely with consumers’ demands for personalized products that align with their values. Health and Well-being are driving consumer preferences and will continue to do so, as presented by Shane Tremble from the Endeavor Drinks Group, a major alcoholic beverage retailer in Australia.
The afternoon session was dedicated to diversity, equity, and inclusivity in the wine industry. Our own unconscious biases create barriers to enter the wine industry, especially for talents from underrepresented groups. Diversity, equity, and inclusivity is not just about social justice, but is a real business loss, especially as the wine consumer base becomes more and more diverse. How can we make sure to meet the needs of our consumers if we don’t really understand them and their needs?
A large portion of the meeting was dedicated to different aspects of climate change and how the wine industry will be able to continue doing business. A representative from a major insurance company presented on her company’s strategy to climate change, and managing risks associated with a changing climate – from special loans for businesses to lower their carbon footprint and greenhouse emissions to ways to manage physical risks such as flooding and bush fires, this presentation was eye-opening. Tools already available for growers, such as high-resolution weather data, provide action-able data for e.g., harvesting or irrigation. Clonal selection, vine training systems and better suited varieties and rootstocks are another tool in the toolbox to adapt to climate change, particularly to higher temperatures and increased incidences of drought, as demonstrated by Dr. Cornelis van Leeuwen from Bordeaux Sciences Agro.
Ending with the conference’s gala dinner, this first day proved to be full of insights and what the future may bring.
The next day started off with the fresh science session, including research on how changing climate will also change insect and disease pressure: Using the example of sooty mold and scale insects, Dr. Paul Cooper presented data and models that show how warmer temperatures will influence occurrence of scale insects and subsequent sooty mold. Similar scenarios could become more prevalent in PA as well, as for example late harvest insect problems could appear at an earlier stage during berry ripening (see also this blog post by Jody Timmer).
On the enology-side, several presentations were given to look at smoke-taint remediation of wines, alternatives to bentonite fining with grape seed powder, and the mechanisms underlying autolytic flavors in sparkling wines. A particular interesting, but also terrifying talk was given by Caroline Bartel from the AWRI on increasing SO2tolerance of Brettanomyces bruxellensis strains: Over the past 3 years, the AWRI has seen an increased number of Brettanomyces strains that show greater tolerance to SO2, some exceeding 1 mg/L molecular SO2!
Biosecurity is a big topic for Australian grape growers, as almost all vineyards are own-rooted, including some of the oldest productive vineyards in the world being over 100 years old! This history is however under threat, as phylloxera has arrived in Victoria and New South Walesa few years ago. Managing the biosecurity threats and best practices to protect vineyards from not just phylloxera but also grapevine viruses was the overarching theme of this session. Showing data from the Napa Valley, Dr. Monica Cooper from UC Extension highlighted the importance of clean plant material when it comes to managing grape vine diseases: in a newly planted vineyard, not enough certified disease-free material was available, and hastily organized vines, infected with red blotch virus, were planted alongside healthy vines. Within a few years, 100% of infected vines had to be removed to avoid spreading of the disease into other parts of the vineyard and adjacent vineyards.
The last talk in the session was given by Dr. Antonio R. Grace from the Portuguese Association for Grapevine Diversity, who argues that clonal selection of grapevines may increase efficiency but decreases resilience, complexity, and diversity.
A particular interesting session was focusing on Agricultural Technology or AgTech – robots, drones, and intelligent robot swarms! A particular impressive and eye-opening talk was given by Andrew Bate from SwarmFarm, a farmer in Queensland who now develops and sells farming robots that oppose the trend for “bigger is better”: using a swarming approach (i.e., many smaller robots that operate autonomously for maximized efficiency and adaptability), he showcased how his approach is forward-thinking and sustainable, and fueled by his own experiences as a farmer and grower. If you can check out the videos on the website!
In a similar inspiring manner, Everard Edwards from the CSIRO presented on low-cost drones and sensors and how to use them in the vineyard to support decision-making: for example, a go-pro camera mounted on a small cart, driving along rows, could be used for yield estimation. The technology is already there, but we are still lacking the data algorithm to make sense out of the data.
The day was finished up with the flash poster research presentations of wine science students. From glycosylated flavor compounds locked up in grape skins, to vintage compression and the effect of very high temperatures (over 50°C/122°F) for a short time on grape berry development and tannin content, these talks showcased the breath of wine research in the various Australian research institutions. Following the evening’s theme, the next day’s fresh science included a talk on how to remediate reductive aromas in wines. Among the tested treatments (DAP addition post-inoculation, donor lees added after malo-lactic fermentation, copper addition, macro-oxygenation, and a combination of copper and macro-oxygenation) macro-oxygenation once a day of 1.5 L/min O2for 2 hours yielded the most promising results while copper addition increased the risk of reductive characters developing post-bottling. Similarly, how to easier measure total and free copper in wines and juice was the topic of Dr. Andrew Clark’s presentation. Working at the National Wine and Grape Industry Centerin Wagga Wagga, Dr. Clark developed an easy spectrophotometric method to accurately and precisely measure free and total copper in wines.
Last, a genetic study on Chardonnay revealed that the same clones (clone 95) shows a different number of mutations depending on where it is from.
Besides the many fascinating talks and the impressive trade show, the meeting also offered lots of opportunities to taste Australian wines. I was lucky enough to participate in a guided tasting of a type of fortified wines unique to Australia: Presented with an impressive number of Rutherglen Muscatwines of all ages and classifications, I was able to experience this special wine style, and must admit that I brought back some bottles of these “stickies”. Made from Muscat a Petit Grains Rouge grapes (literally Muscat with little red berries), very ripe grapes, accumulating very high sugar content, are fermented and fortified with grape spirit, then aged from 3 up to 20+ years in barrels. Wines undergo a solera blending, transferring wines slowly from barrel to barrel until bottling. Flavors range from floral, honey and orange peel all the way to viscous, toasted and caramel flavors. If you ever have the opportunity to taste such wines, I would strongly encourage you to do so – even if this is not your style of liking, it is for sure a worthwhile sensory experience!
Outside of the Conference I also had the chance to visit three remarkable places: The National Wine and Grape Industry Center (NWGIC) in Wagga Wagga, University of Adelaide and the Australian Wine Research Institute (AWRI) in Adelaide, and last, but not least, Penfold’s original winery in the Adelaide Hills for a special tour and tasting of the most expensive wine in Australia, the Grange.
By Dr. Molly Kelly, Enology Extension Educator, Department of Food Science
As we approach harvest, we should be reviewing our sanitation protocols both in the vineyard and winery. In this article we will focus on effective cleaning and sanitizing in the winery, specifically winery equipment to make sure certain objectives are met:
- To continually improve wine quality
- To reduce quality concerns
- To ultimately operate cost-effectively…by annually producing both a quality wine and reaching the targeted financial return
- To reduce food safety concerns
Stainless Steel Winery Equipment
During normal service, all grades and finishes of stainless steel may in fact stain, discolor, or attain an adhering layer of grime. What considerations should one take regarding maintaining stainless steel equipment and the related use of cleaners and sanitizers? The frequency and cost of cleaning stainless steel is lower than for many other materials and often out-weighs the higher acquisition costs. Generally, the frequency of cleaning should be determined by the objective to “clean the metal when it is dirty in order to restore its original appearance.”
So, the degree of cleaning depends on the condition of stainless steel equipment:
- Routine Maintenance – mild cleaning
- Mildly aggressive cleaning to remove minor surface dirt: use sponge or bristle brush with a non-abrasive cleaner and warm water; towel dry. To prevent compromising the integrity of the protective oxide coating on stainless steel, only soft-bristle brushes should be used in the case where scrubbing is required.
- More aggressive, for example, grease: repeat above, then use a hydrocarbon solvent such as acetone or alcohol.
- Aggressive cleaning to remove stains or light rust: use a chrome, brass, silver cleaner and mild non-scratching creams and polishes.
- Most aggressive to remove stubborn mineral deposits: use phosphoric acid (10-15% solution) – apply with a soft cloth and let stand; no rubbing. Follow with ammonia and water rinse; rinse with hot water. Note that nitric acid is effective too but tends to degrade gasket material.
General Cleaning and Sanitizing Sequence:
1. Begin with a cold water, high-pressure rinse. Cleaning with high-pressure is most effective when the spray is directed at an angle to surface being cleaned. One may also use warm water (100-109 F) in high-pressure systems; this tends to reduce time.
2. Use a strong inorganic alkaline solution; such alkaline cleaners effectively dissolve acid soils and food wastes. Examples of alkaline cleaning agents are caustic soda (NaOH), soda ash (Na2CO3), trisodium phosphate (TSP) and sodium metasilicate. Carefully follow instructions because such alkalis are very corrosive to stainless steel if used incorrectly. A mild acid (citric) will neutralize alkaline detergent residues, dissolve the mineral deposits and prevent spotting. As a rule, soda ash rinses better than caustic soda.
3. Continue with a cold water, high-pressure rinse.
4. Sanitizer Options:
a. Water and Steam
- Hot water (180 F) and steam are ideal sterilants: they are noncorrosive, penetrative of surfaces, and effective against juice/wine microorganisms.
- Use hot water for 20 minutes (at 180 F).
- If steam, use until condensate from valves reaches 180 F for 20 minutes.
b. Quaternary ammonium compounds (QACs), combined with peroxyacetic acid.
Note that “acid-anionic” sanitizers such as peroxyacetic acid are effective at lower than ambient temperatures; remove biofilms; and are effective against bacterial spores. The low foam characteristics make them ideal for Clean-in-Place (CIP) applications. Although peroxyacetic acid must be used in well-ventilated area, it is ecologically harmless by decomposing into acetic acid, oxygen, and water.
- Rinse: QAC solutions may leave objectionable films on equipment and should be rinsed off with fresh cold water, high-pressure rinse.
- Final rinse: a hot water, high-pressure rinse. Ideally, heat-sterilized water should be used for this final rinse.
- Ozone treatment (optional)
- NOTE: Remember to remove tank valves, take apart and clean prior to harvest.
There are many different barrel cleaning methods:
- High-pressure water, hot or cold
- Caustic chemicals
- SO2 (in any form: wicks, liquid, gas)
- Dry ice blasting
In selecting which method to use, consider the effects on aroma/flavor extraction, tartrate removal, microbial reductions, water usage, power usage, worker safety, and cost.
The following are recommended cleaning and sanitizing sequences, based on barrel status.
New Barrels/Fault-Free Barrels
- Cold water, high-pressure rinse, 1-3 minutes
- High-pressure steam rinse, 1-3 minutes
- Repeat cold and steam rinses twice more
- Either refill with clean wine or
- Fill with water
- add ozone, if available
- follow with water + 45 ppm SO2/90 ppm citrate
- Fill with water
- After 1-4 days, empty and refill with wine or empty and burn sulfur wick, re-bung, and store; or, if using the gas, inject SO2for three to five seconds.
- If the barrel is to be long-term stored, dissolve and add 45 grams of potassium metabisulfite (KMS) and 180 grams of citric acid; then top the barrel with water. Be sure to top the barrel with plain water every couple of weeks. When you’re ready to use the barrel, empty and rinse twice; then fill with wine.
Likely Fault-Free Barrels, but Unsure
- Sodium percarbonate washes (Proxycarb) are an excellent option for addressing potential off-flavors. Citric acid washes are then used to neutralize residual chemicals. Once the barrel has been cleaned, allow the barrel to dry completely on a rack with the bunghole facing down. Sodium percarbonate is better than hydrogen peroxide: it is more stable at application concentration (100-200 mg/L), has improved compatibility with hard water, and reduced foaming tendencies.
- When the barrel is dry, burn 10-20 grams of sulfur wick per barrel; or, if using the gas, inject SO2 for three to five seconds.
- Place either a paper cup, wooden shipping bung, or other in the bunghole.
- Check sulfur level every 3-4 weeks and re-sulfur as necessary.
Tannin and Tartrate Deposit Removal
- Removal of tannins: Alkaline solutions (soaking with 1% sodium carbonate) are most effective in removing tannins from new barrels. If further treatment is necessary, steam and several rinses should be applied.
- Removal of tartrate deposits: scraping is labor intensive and may injure wood. Instead, use a circular spray head. For stubborn deposits, soaking with 1 kg of soda ash and caustic soda in 100 L of water is effective.
- Option 1: Remove from winery and sell for non-wine uses
- Option 2: Clean, sterilize, and re-use, if worth the cost
- Use same rinse cycles as per barrels without faulty aromas or tastes.
- Fill with water, put steam wand in water and bring water to 160-180°F, steam periodically to maintain temperature for 4-6 hours and
- add ozone, if available
- follow with water + 45 ppm SO2/90 ppm citrate
- After 1-4 days, empty and burn sulfur wick, re-bung, and store.
- After 1-4 weeks, rinse and fill with clean water; after 1 week, take samples and then add 90 ppm SO2/180 ppm citrate while doing microbiological assay of samples.
- If samples are negative for spoilage microorganisms, re-use barrel, but sample periodically.
Bottling Room Equipment
The bottling and packaging function is one of the most critical steps in wine production because there are many opportunities for problems (people with different responsibilities, multiple wines to bottle, and operation and maintenance of multiple equipment stations).
Are sterile bottling rooms necessary? No, but the bottling area should be screened-off from fermentation areas and excessive air movement, and the room itself should have easily sanitized floors, walls, and ceilings.
General Cleaning and Sanitizing Sequence:
- Cold water, high-pressure rinse
- Mild alkaline detergent solution
- Cold water, high-pressure rinse
- Quaternary ammonium compounds (QACs), combined with peroxyacetic acid.
- Cold water, high-pressure rinse
- Sanitization: Hot water and steam used to sanitize bottling line
- 80-90F for 30 minutes
- 180F for 20 minutes; or
- Ozone for 20-30 minutes; or
- Use of iodophors (iodine-based sanitizers): broad-spectrum – active against bacteria, viruses, yeasts, molds, fungi. Follow instructions carefully to avoid potential TCA problems; follow with a hot water, high-pressure rinse.
Prior to bottling, add enough SO2to ensure enough free SO2for 0.8 ppm molecular SO2. Add a little bit extra – to account for free SO2loss during bottling. Generally, target a free SO2that is 10 to 15 ppm higher than the level of free SO2needed for 0.8 ppm molecular SO2. Also, target more or less depending on trauma of bottling method (O2pick up)
Recommendations during operation of the bottling line:
- Wine spills as a source of contamination should be countered by regular and proper cleaning
- Filter-pad trays should be emptied often, and related wine spills quickly rinsed away with a sanitizing agent
- Fill bowls: Mist filler spouts with 70% ethanol to inhibit microbial growth
- Corker: will likely have spilled wine, so use ethanol misting of corker jaws during bottling
- Floor drain gutters should be kept clean by frequent rinsing
- Activity: Limit number of people around the filling/corking area
- Daily sanitation…hot water or steam…20 minutes at 180F
- At least weekly, clean with caustic cleaners followed by hot water sanitation.
- Collect bottles for analysis hourly and immediately after start-up and breaks.
Butzke, C., Barrel Maintenance, Dept. of Food Science, Purdue University, 2007.
Carter, James, There’s a Right Way to Clean and Sanitizing your Facility, Food Quality.com
Donnelly, David M, Airborne Microbial Contamination in a Winery Bottling Room, Am. J. Enol Vitic, Vol 28, #3, 1977
Fugelsang, Kenneth; Edward, Charles G. Wine Microbiology, 2nd Edition, 2010. Springer-Verlag New York Inc. (Chapter 9, Winery Cleaning and Sanitizing)
Marriott, Norman G.; Gravani, Robert B. Principles of Food Sanitation, 5thEdition, 2006. Springer Science + Business Media, Inc. (pp 361-367)
Howe, P., ETS Laboratories, SOWI “Current Issues” Workshops March 2011.
Menke, S., Cleansers and Sanitizers, Penn State Enology Extension, 2007.
Tracy, R. and Skaalen, B. Jan/Feb 2009. Bottling-last line of microbial defense. Practical Winery and Vineyard
Worobo, Randy W., Non-chlorine Sanitizer Options for the Wineries, 33th Annual New York Wine Industry Workshop
Zoecklein, B. et al, Wine Analysis and Production, Aspen Publishers, 1999.
Barrel Care http://www.boswellcompany.com/barrel-care/
Maintaining and Cleaning Stainless Steel http://www.evapco.eu/sites/evapco.eu/files/white_papers/40-Cleaning-Stainless-Steel.pdf
Stainless Steel – Cleaning, Care and Maintenance http://www.azom.com/article.aspx?ArticleID=1182
Taking Care of Your Barrels https://barrelbuilders.com/wp-content/uploads/2016/06/06-16-Barrel-Care.pdf
On March 5, 2019, Penn State researchers and Extension personnel presented research findings and provided five-minute overviews of upcoming studies at the 2019 Wine Marketing & Research Board Symposium, held in conjunction with the Pennsylvania Winery Association Annual Conference.
In this post, we have included short summaries of what each presenter discussed during their session along with a PDF/access to their presentation.
Under-vine cover crops: Can they mitigate vine vigor and control weeds while maintaining vine productivity?
Presented by Michela Centinari, Assistant Professor of Viticulture, Suzanne Fleishman, Ph.D. Candidate, and Kathy Kelley, Professor of Horticultural Marketing and Business Management
Michela, Suzanne, and Kathy discussed research conducted at Penn State related to the use of under-vine cover crops as a management practice alternative to herbicide or soil cultivation. Michela reviewed potential benefits of under-vine cover crops, such as reduction of excessive vegetative growth, weed suppression, and reduced soil erosion. She showed how the selection of cover crop species depends on the production goals of a vineyard, climate, vine age, and rootstock. Suzanne presented results from her research project. She is investigating above- and belowground effects of competition between a red fescue cover crop and Noiret grapevines, comparing responses between vines grafted to 101-14 Mgt vs Riparia rootstocks. Surveys will be administered to Pennsylvania grape growers and wine consumers in the Mid-Atlantic region. Growers will be asked to respond to questions about interest in using cover crops and benefits that could encourage their use. The consumer survey will focus on learning whether cover crops use would impact their purchasing decision and if they would be willing to pay a price premium for a bottle of wine to offset additional production costs.
Impact of two frost avoidance strategies that delay budburst on grape productivity, chemical and sensory wine quality.
Presented by Michela Centinari, Assistant professor of Viticulture
Crop losses and delays in fruit ripening caused by spring freeze damage represent an enormous challenge for wine grape producers around the world. This multi-year study aims to compare the effectiveness of two frost avoidance strategy (application of a food grade vegetable oil-based adjuvant and delayed winter pruning) on delaying the onset of budburst, thus reducing the risk of spring freeze damage. Our objectives are to: i) evaluate if the delay in budburst impacts grape production and fruit maturity at harvest, as well as chemical and sensory wine properties; ii) elucidate the mechanism of action of the vegetable oil-based adjuvant through an examination of bud respiration and potential phytotoxic effects; and iii) assess the impact of the two frost avoidance strategies on carbohydrate reserve storage and bud freeze tolerance during the dormant season.
Toward the development of a varietal plan for Pennsylvania wine grape growers.
Presented by Claudia Schmidt, Assistant Professor of Agricultural Economics, and Michela Centinari, Assistant Professor of Viticulture
Claudia Schmidt is a new Assistant Professor of Agricultural Economics with an extension appointment at Penn State. Claudia used the opportunity of the symposium to introduce herself to the industry. In her presentation, she first gave an overview on what and where Pennsylvanians buy their wines and spirits. She then talked about the research needed to develop a varietal plan for the Pennsylvania grape and wine industry to match existing and future grape production and variety suitability with anticipated consumer demand. The immediate next steps on her research agenda are to develop a baseline survey of grape production in Pennsylvania and, in collaboration with Michela Centinari, region specific cost of production of grapes.
Survey for grapevine leafroll viruses in Pennsylvania: How common is it, and how is it effecting production and quality?
Presented by Bryan Hed, Research Technologist
This is a continuing project funded by the PA Wine Marketing and Research Board, that has focused on the determination of the incidence of grapevine leafroll associated virus 1 and 3 (the two most economically important and widely distributed of the leafroll viruses) in commercial vineyard blocks of Cabernet franc, Pinot noir, Chardonnay, Riesling, and Chambourcin, across the Commonwealth. Over two years, the survey has shown that grapevine leafroll associated viruses 1 and/or 3, were present in about a third of the vineyard blocks examined. Infection of grapevines by grapevine leafroll-associated viruses can have serious consequences on yield, vigor, cold hardiness, and most notably fruit/wine quality. Bryan also discussed a second phase of the project, anticipated to continue for at least another two years within 6 vineyard blocks of Cabernet franc, identified in the survey. In these vineyards, we plan to plot the spread of these viruses, examine and report their effects on grapevine vegetative growth, yield, and fruit chemistry, and characterize the influence of inter- and intra-seasonal weather conditions on virus-infected grapevine performance.
Integrating the new pest, spotted lanternfly, to your grape pest management program.
Presented by Heather Leach, Extension Associate
Spotted lanternfly (SLF) is a new invasive planthopper in the Northeast U.S. that threatens grape production. Heather covered the basic biology, identification, and current distribution of SLF. She also presented on the economic impact of SLF in the grape industry and ways to manage SLF in your vineyard. SLF can feed heavily on vines causing sap depletion in the fall which has resulted in death of vines, or failure of vines to set fruit in the following year. While biological controls such as pathogens and natural enemies along with trapping and behaviorally based methods are being researched, our current management strategy relies on using insecticides sprayed in the vineyard. Heather showed results from the 2018 insecticide trials conducted against SLF, with efficacy from several products including bifenthrin, dinotefuran, thiamethoxam, carbaryl, and zeta-cypermethrin. You can read more about the results from this trial here: https://extension.psu.edu/updated-insecticide-recommendations-for-spotted-lanternfly-on-grape
Five-minute research project overviews
Impact of spotted lanternfly on Pennsylvania wine quality.
Presented by Molly Kelly, Extension Enologist
The Spotted Lanternfly (SLF) presents a severe problem both due to direct damage to grapevines as well as their potential to impact wine quality. Insects are known to produce or sequester toxic alkaloid compounds. The objectives of this study include characterizing the chemical compounds in SLF and production of wines with varying degrees of SLF infestation. We can then provide winegrowers with recommendations for production of wine from infested fruit. Toxicity studies will be conducted to determine the levels of toxic compounds in finished wine, if any, using a mouse bioassay.
Exploring the microbial populations and wild yeast diversity in a Chambourcin wine model system.
Presented by Chun Tang Feng, M.S. Candidate, and Josephine Wee, Assistant Professor of Food Science
In Dr. Josephine Wee’s lab, we are interested in the microbial population and diversity associated with winemaking. When it comes to wine fermentation, not only are commercial yeasts involved in this process, but also many indigenous yeasts. Our research goal is to isolate the wild yeasts and assess their feasibility of wine fermentation. We are expecting to explore the unique yeast strains from local PA which are able to make a positive impact on wine flavor.
Rotundone as a potential impact compound for Pennsylvania wines
Presented by Jessica Gaby, Post-Doctoral Scholar and John Hayes, Associate Professor of Food Science
This study will examine Pennsylvania consumers’ perceptions of rotundone with the goal of determining whether a rotundone-heavy wine would do well on the local market. This will be examined from several different perspectives, including sensory testing of rotundone olfactory thresholds, liking and rejection thresholds for rotundone in red wine, and PA consumer focus groups. The ultimate aim of the study is to determine the ideal concentration of rotundone in a locally-produced wine that would appeal to PA consumers.
Defining regional typicity of Grüner Veltliner wines
Presented by Stephanie Keller, M.S. Candidate, Michela Centinari, Assistant Professor of Viticulture, and Kathy Kelley,
Grüner Veltliner(GV) is a relatively new grape variety to Pennsylvania, and while climatic conditions are favorable to its growth, the Pennsylvania wine industry is still becoming familiar with the varietal characteristics of GV grown and produced throughout the state. This study focuses on defining typicity of Pennsylvania-grown GV wines. Typicity is described as the perceived representativeness of a wine produced from a designated area, and defining typicity can improve wine marketing strategies. This study uses multiple experimental sites across the state to create wines from a standardized vinification method. The wines will be analyzed using both instrumental and human sensory methods.Surveys will be administered to Pennsylvania grape growers and white wine consumers in the Mid-Atlantic region. Growers will be asked their interest in growing GV and what perceived and real barriers may impact their decision to grow the variety. The consumer survey will focus on understating how to introduce them to a wine varietal they may be less aware of and what promotional methods may encourage them to purchase the wine.
Boosting polyfunctional thiols and other aroma compounds in white hybrid wines through foliar nitrogen and sulfur application?
Presented by Ryan Elias, Associate Professor of Food Science, Helene Hopfer, Assistant Professor of Food Science, Molly Kelly, Extension Enologist, and Michela Centinari, Assistant Professor of Viticulture
The quality of aromatic white wines is heavily influenced by the presence of low molecular weight, volatile compounds that often have exceedingly low aroma threshold values. Polyfunctional varietal thiols are an important category of these compounds. This project aims to provide research-based viticultural practices that could lead to increases in beneficial varietal thiols in white hybrid grapes. The expected increase in overall wine quality will be validated both by measuring the concentrations of these desirable compounds (i.e., thiols) in finished wines using instrumental analysis and by human sensory evaluation, thus providing a link between the viticultural practice of foliar spraying and the improvement of overall wine quality.
By: Conor McCaney, Graduate Assistant, Department of Food Science & Technology
The winemaking process is a dynamic one: from crush, to fermentation, on to post fermentation cellar procedures, aging, and bottling. Each step along the way allows for the potential ingress of oxygen, whether wanted or not. While oxygen is considered by many to be the enemy of wine, this is not always the case. In fact proper use of enological oxygen at crucial steps in the winemaking process is paramount to wine development. That said, many winemakers dutifully aim to eliminate it from the process altogether particularly in partial tank headspace. Proper gassing regimens and selection of the correct gas for a particular application is something that many do not do well and fail to fully understand the principals at play. Managing proper inert gas procedures is tricky. Most protocols are generally arbitrary ones copied from bad information and the proliferation of poor techniques passed on anecdotally from winemaker to winemaker. In general it is a procedure that is often over looked and never given much thought. This usually means the use of a high pressure cylinder (most often nitrogen), and a ¼” or ½” hose that is allowed to run for an arbitrary amount of time, generally 15 to 20 minutes. The results are the improper use of inert gases from the failure to measure gas volumes delivered (using a flowmeter), monitoring results with the use of a dissolved oxygen meter, using an under or oversized delivery system and unsubstantiated cost analysis pertaining to gas type and volume needed.
Typical gas choices are: carbon dioxide, nitrogen, and argon. Most wineries choose to use carbon dioxide and nitrogen because they believe it provides the best cost-benefit in terms of oxygen displacement per unit cost. This is not the case. To understand this, we must first delve into some fundamental principles of gases. In the wine industry, we typically use gas by volume, either in standard cubic feet or molar volume delivered from a standard steel pressurized cylinder in which the gas is compressed. These gas volumes are usually measured at 25°C and 1 atm. If you happen to purchase gas by the pound it is necessary to divide the gas by its molecular weight before you can compare gases to one another. The approximate molecular weights are: 40 g/mole for argon (Ar), 44 g/mole for carbon dioxide (CO2), 28 g/mole for nitrogen (N2), and 29 g/mole for air. One mole of any of these gases measured at standard pressure (1atm) and temperature (25°C) occupies one molar volume, roughly equivalent to 22.4 liters, 5.92 gallons, or 0.8 standard cubic feet. Using the ideal gas law PV = nRT the behavior of gases can be described in which pressure and volume is a fixed proportion in relation to the number of moles of gas at absolute temperature. This indicates that gas molecules take up the same amount of space regardless of their mass when they are at the same temperature and pressure (Avogadro’s Law). Thus one mole of any gas contains the same number of molecules (i.e., 6.02 x 1023). This also indicates that the head space in a tank, barrel, or other container will fluctuate regularly throughout the day in response to temperature and pressure changes. Tanks that are kept outside experience greater temperature changes throughout the day compared to a tank kept inside at a constant temperature. Changes in barometric pressure and temperature can cause the headspace in a tank to pump 3% to 7% of its volume in and out daily. This ultimately means that the headspace in a tank is not a static system and could be constantly changing.
Air is roughly composed of 78% nitrogen, 21% oxygen, and 1% argon, so in essence nitrogen is air without the oxygen. In any gassing procedure it is ideal to reduce the percentage of oxygen in the headspace to below 1% or even below 0.5% to inhibit the growth of aerobic microbes and prevent wine oxidation. The most commonly used gas in winemaking is nitrogen (N2) with a molecular weight (MW) of 28 g/mole making it moderately lighter (less dense) than air at 29 g/mole MW. Graham’s law of diffusion (also known as Graham’s law of effusion) states that the rate of effusion of a gas is inversely proportional to the square root of its molar mass at constant temperature and pressure. This principle is often used to compare the diffusion rates of two gasses such as nitrogen and air. The diffusion rates of nitrogen and air are almost identical meaning that nitrogen does not provide adequate layering, but rather readily mixes with air and does not remain in contact with the wine surface for an extended period of time. This also means that in order to reduce the O2level from 21% to less than 1%, the headspace needs to be flushed with a volume of nitrogen that is five times the volume of the headspace. So if the tank has a 100 gallons of head space it would take 500 gallons of nitrogen to reduce the O2level from 21% to below 1%. The cost of nitrogen is approximately $0.05 per cubic foot (Praxair, Inc). However, because nitrogen requires five times the volume equivalents to reduce the O2percentage from 21% to less than 1%, the cost to gas a barrel (60 gallons) is $2.00, 100 gallons of headspace is $3.34 and 1,000 gallons of headspace is $33.42. This is significantly higher than the cost of using argon for the same O2reduction in the equivalent headspace volumes. This is why headspace gassing with nitrogen requires a substantial effort and time commitment on the part of the winemaking team to be effective. It takes substantially more nitrogen and a greater application time compared to argon to achieve the same reduction in oxygen percentage with a shorter effective shelf life.
In contrast to nitrogen is carbon dioxide (CO2), which is significantly heavier than air at 44 g/mole compared to 29 g/mole and by Graham’s law has a much slower rate of diffusion compared to air. This allows for a more significant displacement of air compared to nitrogen. However, when CO2is delivered from a compressed tank, it is difficult to achieve the desired laminar flow necessary for successful layering. This results in substantial mixing of CO2and air. A more effective alternative for CO2delivery is dry ice (solid CO2) which leads to more efficient layering of CO2and subsequent displacement of air but does not form a permanent layer. However, it should be noted that CO2cannot be considered inert in the same way as nitrogen and argon. Because of Henry’s Law, which states that the solubility of a gas is directly proportional to the partial pressure of the gas above the solution, CO2readily dissolves into wine under standard conditions and its solubility can be increased or decreased with changes in pressure. This dissolution of CO2into the wine causes the pressure in the tank to fluctuate and results in the intake of air from the outside environment through an airlock to replace the lost volume of gaseous CO2. If there is no vacuum release valve on the tank, this could cause the tank to implode. Carbon dioxide dissolved in the wine will also alter the acid, flavor, and textural profile of the final wine. Carbon dioxide is much more effective when deployed early in the winemaking process at juice stage or when the wine is young as there will be substantial time to allow excess dissolved CO2to come out of solution. The use of dry ice to protect grape must is an effective way to protect wine must from excess oxygen exposure, deter fruit flies, and subsequently cool the must.
This leaves argon with a molecular weight of 40 g/mole, making it substantially heavier than air (29 g/mole) and similar in weight to CO2but more inert. A major opposition to the use of argon regularly in wine production is because it is significantly more expensive compared to the other two gases. It is true that when purchasing gas by volume argon is roughly three times as expensive as nitrogen or carbon dioxide. However it is much more effective at displacing air and creating a more permanent blanket that remains in contact with the wine surface longer while also remaining inert compared to CO2. Less volume is also needed to achieve the same desired results. At approximately $0.11 per cubic foot (Praxair, Inc) not including daily tank rental fee, a barrel (60 gallons) can be completely gassed with argon for $0.88, 100 gallons of head space for $1.47, and 1,000 gallons of headspace for $14.71. This cost is relatively insignificant to a winery’s bottom line in terms of the degree of quality preservation that argon can provide.
When using any of the gases discussed previously, it is important to select the proper pressure gauge, hose diameter, hose length, flowrate, and the use of a t-valve in order to deliver the gas under laminar conditions. The use of a lower velocity, will encourage laminar flow delivery and reduce any chance of turbulence and subsequent mixing with air, thus creating a more layered effect.
It is ideal to keep the flow velocity to 1 meter per sec or less. To determine the velocity divide the volumetric flow rate in cubic meters per second by the cross sectional area in meters of the hose being used. If using cubic feet instead of cubic meters, perform the same calculation but convert the units from cubic meters to cubic feet and meters to feet. Table 1 shows that it is best to use a 1.5” or 2” diameter line with a t-valve to deliver an adequate amount of gas in a reasonable amount of time. This will require the use of an oversized regulator compared to the typical 0.25” regulator used on most compressed gas cylinders.
In essence it is best practice to recommend the use of argon as the headspace gas for the majority of wine production processes. Carbon dioxide and nitrogen have their respective roles but when it comes to headspace gassing argon it the number one choice. In the production of high quality wine, it is imperative to establish proper gassing procedures. This includes the successful training of staff in all aspects of gassing procedures and the selection of the correct gas for the appropriate task. This also requires selecting the correct regulator size, hose diameter and length, the use of T-valves, measuring gas flow using a flowmeter, and finally verifying results with the use of a dissolved oxygen meter to monitor oxygen levels in the tank headspace pre and post gassing. The proper investment of time and resources in this often overlooked area of winemaking can have a profound effect on wine quality and preservation in the long run. It can also reduce long term costs by reducing the amount of gas and time required to achieve the desired reduction in the amount of oxygen present in a tank headspace.
By Dr. Molly Kelly, Enology Extension Educator, Department of Food Science
As harvest comes to a close we have planned which wines will be going through malolactic fermentation (MLF). This article provides some information to assist you in dealing with a potentially difficult MLF.
Malolactic fermentation (MLF) is a process of chemical change in wine in which L-malic acid is converted to L-lactic acid and carbon dioxide. This process is normally conducted by lactic acid bacteria (LAB) including Oenococcus oeni, Lactobacillus spp. and Pediococcus spp. O.oeni is the organism typically used to conduct MLF due to its tolerance to low pH, high ethanol and SO2. Most commercial strains are designed to produce favorable flavor profiles.
Although inoculation with a commercial starter is recommended, MLF may occur spontaneously. The lag phase associated with spontaneous MLF may increase the risk of spoilage organisms as well as the production of volatile acidity. Inoculation with a LAB culture can help avoid these problems by providing the cell population needed to successfully conduct MLF (more than 2×106 cells/mL). The compatibility of yeast and LAB should be taken into account since failed MLF may be due to incompatibility between these two organisms.
The key to a successful MLF is to manage the process and to monitor the progress. Although there has been extensive research on the MLF process, it may still be difficult to initiate at times. The possible causes of difficult MLF have been studied less extensively than those of stuck/sluggish alcoholic fermentation. In this article, factors that may influence the start and successful completion of MLF will be discussed.
The main chemical properties that influence MLF are well known: pH, temperature, ethanol and SO2 concentration. A study by Vaillant et al (1995) investigating the effects of 11 physico-chemical parameters, identified ethanol, pH and SO2 as having the greatest inhibitory effect on the growth of LAB in wine.
Generally, LAB prefer increased pH’s and usually, minimal growth occurs at pH 3.0. Under winemaking conditions, pH’s above 3.2 are advised. The pH will determine the dominant species of LAB in the must or wine. At a low pH (3.2 to 3.4) O. oeni is the most abundant LAB species, while at higher pH (3.5 to 4.0), Lactobacillus and Pediococcus will out-number Oenococcus.
MLF is generally inhibited by low temperatures. Research demonstrates that MLF occurs faster at temperatures of 200 C (68˚F) and above versus 150C (59˚F) and below. In the absence of SO2 the optimum temperature range for MLF is 23-250C (73.4˚F-77˚F) with maximum malic acid conversion taking place at 20-250C (68˚F-77˚F). However, with increasing SO2 levels, these temperatures decrease and 200C (68˚F) may be more acceptable.
LAB are ethanol-sensitive with slow or no growth occurring at approximately 13.5%. Commercial O. oeni strains are preferred starter cultures due to tolerance to ethanol. The fatty acid composition of the cell membrane of LAB can be impacted by ethanol content.
LAB may be inhibited by the SO2 produced by yeast during alcoholic fermentation. A total SO2 concentration of more than 50 ppm generally limits LAB growth, especially at lower pH where a larger portion of SO2 is in the antimicrobial form. Generally, it is not recommended to add SO2 after alcoholic fermentation if MLF is desired.
Some of the lesser known factors impacting MLF are discussed below.
MLF can be inhibited by medium chain fatty acids (octanoic and decanoic acids) produced by yeast. It is difficult to finish MLF when octanoic acid content is over 25 mg/L and/or decanoic acid is over 5 mg/L. Bacterial strains that tolerate high concentrations of octanoic and decanoic acids may be important in successful MLF. It is important to check your supplier regarding strain specifications. Yeast hulls may be added before the bacteria are inoculated (0.2g/L) to bind fatty acids. Yeast hulls may also supply unsaturated fatty acids, amino acids and assist with CO2 release.
Some fungicide and pesticide residues may negatively impact malolactic bacteria. Residues of systemic pesticides used in humid years to control botrytis can be most detrimental. Care should be taken in harvest years with high incidence of botrytis. Winegrowers should be familiar with sprays used on incoming fruit and also adhere to pre-harvest intervals.
Lees found at the bottom of a tank can become compacted due to hydrostatic pressure, resulting in yeast, bacteria and nutrients being confined to the point that they cannot function properly. Larger tank sizes may contribute to increased delays in the start of MLF. This inhibition of the start of MLF can be remedied by pumping over either on the day of inoculation or on the second day after inoculation of the bacteria.
Alternatively, contact with yeast lees can have a stimulating effect on MLF. Yeast autolysis releases amino acids and vitamins which may serve as nutrients for LAB. Yeast polysaccharides may also detoxify the medium by adsorbing inhibitory compounds. A general recommendation is to stir lees at least weekly to keep LAB and nutrients in suspension.
Residual levels of lysozyme may impact MLF. Follow the supplier’s recommendations regarding the required time delay between lysozyme additions and the inoculation of the commercial MLF culture. Strains of O. oeni are more sensitive to the effects of lysozyme compared to strains of Lactobacillus or Pediococcus.
Malic acid concentration
Malic acid concentrations vary between grape cultivars and may also differ from year to year in the same grape cultivar. MLF becomes increasingly difficult in wines with levels of malic acid below 0.8g/L. In this case a ML starter culture with high malate permease activity or a short activation protocol is recommended. Check with your supplier to ensure that the chosen strain has these attributes if needed.
Wines with levels above 5 g/L malic acid may start MLF, but may not go to completion. This may be due to inhibition of the bacteria by increasing concentrations of L-lactic acid derived from the MLF itself.
Difficult MLF can result from insufficient nutrients necessary for LAB growth. Since yeast can reduce available nutrients for LAB, time of inoculation is important to avoid competition for nutrients. The addition of nutrients when inoculating for MLF is especially important if the must and wine has low nutrient status or if yeast strains with high nutritional requirements are used. The addition of bacterial nutrients can help ensure a rapid start and successful completion of MLF.
Research demonstrates that the longer it takes to initiate MLF, there is a greater risk for Brettanomyces growth. Some inoculate during alcoholic fermentation (AF) to avoid this problem. Co-inoculation involves adding malolactic starter 24 hours after AF starts. By controlling microbial populations, the growth of spoilage organisms such as Brettanomyces may be inhibited.
Note that inorganic nitrogen (diammonium phosphate) cannot be used by LAB. Check with your supplier for the optimum nutrient product for your particular MLF needs.
Malolactic bacteria are sensitive to excessive amounts of oxygen. The bacteria should not be exposed to large amounts of oxygen after AF is complete. Micro-oxygenation may have a positive impact on the completion of MLF. This impact may be due to the gentle stirring associated with micro-oxygenation that keeps LAB and nutrients in suspension rather than the exposure to oxygen itself.
Some red grape cultivars may have difficulty completing a successful MLF. Some varieties that may experience increased MLF problems include Merlot, Tannat and Zinfandel. This may be related to certain grape tannins negatively impacting the growth and survival of LAB.
Polyphenols can have either stimulatory or inhibitory effects on the growth of wine LAB. This effect depends on the type and concentration of polyphenols as well as on the LAB strain. The tannin fraction of wine tends to complex with other compounds, minimizing their inhibitory effects on MLF. However, in wines that contain a large amount of condensed tannins only, LAB are increasingly inhibited.
MLF nutrients containing polysaccharides have been shown to minimize this effect. This may be due to interactions between the polysaccharides and tannins.
MLF difficulties are usually due to a combination of factors. A stuck or sluggish MLF is usually not the result of one factor alone. It is important, therefore, to both understand and manage the MLF process at each step of the winemaking process. Proper measurement of the process is also vital to be aware when MLF is not proceeding as desired.
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