Bryan Hed, Lake Erie Regional Grape Research and Extension Center, Penn State University
With this blog I would just like to briefly reflect on the 2020 growing season as well as present a few updates from research and industry that may affect how we tackle 2021. To be sure, this past growing and harvest season had its own challenges, dealing with COVID-19 restrictions and staying healthy. I hear a vaccine is in the works for the near future that may help us get through this soon, possibly before bud break next year. That said, I would like to take a look back at 2020’s weather and how it may have affected grape disease development this year. In Table 1 we report monthly precipitation at various locations throughout the Commonwealth.
Table 1. Monthly precipitation (inches) recorded from June to October 2020 at several PA locations (from http://newa.cornell.edu/).
|North East (Northwest)||4.54||3.44||4.25||2.41||1.77||6.82|
|State College (North Central)||2.56||5.44||1.16||1.96||2.45||2.95|
|Scott Township (Northeast)||2.60||2.53||3.68||4.73||2.70||3.24|
|Pittsburgh airpt (Southwest)||2.19||2.09||3.10||5.57||0.92||3.29|
|Biglerville (South Central)||2.16||2.47||2.48||3.39||2.29||3.53|
|Philadelphia airpt (Southeast)||2.20||3.21||5.54||8.53||4.20||4.10|
For most locations examined, the first thing that struck me of course was the drier weather throughout most of state, for most of the season. One of the biggest challenges many PA growers below I90 have had to deal with in recent years, has been excessive rainfall and the downy mildew and late season bunch rots that come with it. In some years, growers may have had to throw ‘everything but the kitchen sink’ at controlling downy mildew and were running through the inventory of FRAC groups to control it AND try to manage resistance at the same time. And, when you’re running a small acreage farm, you may not be able to afford to keep an entire inventory of FRAC groups in your fungicide lineup, even with the minimum amounts of each pesticide you can buy. When you can no longer use mancozeb products (past 66 days before harvest) and Ziram isn’t as effective, you have Captan and copper. But Captan and copper can cause problems with fermentation if residues are too high at harvest, so you have to use them with caution late in the season. Ridomil Gold is wonderful but its only sold with mancozeb or copper with a 66 or 42 day preharvest interval. And, there’s materials like Revus, Ranman, Zampro, and the phosphorous acids, which are great, but they too have their preharvest intervals and must be rotated to manage resistance, or we’ll lose them altogether. Note too, I did not mention the strobilurins like Abound and Pristine, and Reason (another FRAC 11 material) for reasons I elaborate on below.
In 2020, the May, June, and July rainfall totals don’t look like they were too troublesome and in some locations it was actually quite dry. Still, some southern locations had a very wet August and September as far as total rainfall is concerned, but the timing of the rainfall was about the best you could hope for. For example, the high August rainfall at Breinigsville and Allentown was mostly in early August at the beginning or just before ripening began. September rainfall was concentrated at the very end of the month, after some varieties had likely been harvested. So even though rainfall totals for August and September for many locations in the Southeast were well above average, most of that rain fell along the edges or just outside the ripening period, when fruit are most susceptible to late season bunch rots. So, despite the other challenges in 2020, it would appear that the weather was a little more cooperative for a change.
Since downy mildew and late season fruit rot management will continue to be a major challenge for PA growers in years to come, we recommend that every serious grower obtain a copy of the NY and PA Pest Management Guidelines for Grapes. A new, updated 2021 version will be hot off the presses early next year. You can purchase one through Cornell University press.
…And now for a couple of research updates
- Evaluation of a new fungicide for powdery mildew control
There’s a new sterol biosynthesis inhibitor fungicide called Cevya. Cevya is in the same FRAC 3 group as Tebuzol, Tebustar, Rally, Mettle, Rhyme, Viticure, Procure, Trionic, the difenoconazole products (Revus Top, Aprovia Top, Quadris Top, Inspire Super), and many, many more. It was approved for use in PA last year and is now approved for use in New York (except Long Island).
If it’s a member of an old chemistry class, what’s so special about Cevya??? Cevya is good to excellent on powdery mildew, from recent results of several trials in PA and NY. This is in contrast to some of the older members of this group that may have slipped a bit with respect to powdery mildew control over the past several decades, due to resistance. However, 2020 was the first year of trial work for black rot control with this product: like other chemistries in this group, Cevya provided excellent control of black rot on Concord and Chambourcin fruit, providing complete control of this disease when applied either before infection (as a preventative) or up to 5 days after infection (as a post infection, curative application). We plan to do more trial work with Cevya in 2021 to further confirm its powdery mildew and black rot efficacy. Unfortunately, there’s a caveat: Cevya is not currently labeled for use on labrusca or labrusca hybrid grapes….ONLY VINIFERA (read the label). However, label expansion is anticipated, so stay tuned! In two years of our trials to evaluate phytotoxicity to native and hybrid grapes (recall the caution with difenoconazole use on Concord and some hybrids), Cevya appears to present no injury issues to Concord, Niagara, Chancellor, Chambourcin, Vignoles, and Vidal grapes, even when applied multiple times on a 14 day schedule, at double the label rate, with a penetrating surfactant. However, we will have to wait for potential label expansion before we consider using Cevya on those natives and hybrids.
2. Mechanized leaf removal in the fruit zone
We also continue to examine mechanized defoliation of the fruit zone (at ‘just before bloom’ and at ‘fruit set’) for effects on late season bunch rot development. Our results over the last several years utilizing air pulse leaf removal systems, have shown consistently that mechanical fruit zone defoliation (at either timing), as part of an IPM program with effective fungicides, will help to reduce late season bunch rots over fungicides alone, on susceptible varieties like Pinot Noir/Gris, Riesling, Chardonnay, and Vignoles. Trellis systems like ‘vertical shoot position’ and ‘4-arm kniffen’, that produce more two-dimensional canopies, tend to maximize the beneficial effects of mechanized defoliation over that of a high wire no-tie system that produces a more three-dimensional canopy. In other words, if you want to get the best bang for your buck from mechanized leaf removal, it appears the more upright, 2-dimensional trellis systems are the way to go.
In 2020, we initiated a trial with Riesling, to examine 4 clones (239, 198, 110, and 90) and two hybrids of Riesling (Geisenheim and NY81) all interplanted and replicated (5x) in the same vineyard. Plots were 3 panels long (12 vines) and all were cane pruned and thinned to 96 shoots per panel (per four vines; 4 shoots per foot of row). We applied one of three treatments to each panel in each plot of each variety/clone for Botrytis bunch rot control; i) fungicides only (check), ii) fungicides plus mechanized defoliation in the fruit zone (MD) at pre bloom, and iii) fungicides plus mechanized defoliation in the fruit zone (MD) at just after fruit set (post bloom); Results of the early defoliation, utilizing the air-pulse system, can be seen in Figures 1A and B.
Results: For all varieties combined, MD reduced rots by 46-50% over fungicides alone, harmonizing with results from other trials with other varieties in past years. However, timing was not important; it didn’t matter if you applied the MD before or after bloom, both timings were equally effective at reducing bunch rot. Also, there was no effect of MD on yield. This is important because pre bloom fruit zone leaf removal by hand, has been shown to reduce cluster weights and yield in some of our past trials. That was not the case in this experiment with the air-pulse system; with all varieties/clones combined, yields were identical, regardless of treatment.
When we look at all individual varieties and clones for damage from bunch rot, we found that NY81 (a Riesling hybrid with Cayuga) was the least rot prone and had the largest yields. The other hybrid, Geisenheim (a Riesling hybrid with Chancellor), was most rot prone, largely a result of powdery mildew damage which was a big factor in the bunch rot that developed later from it. The four Reisling clones fell somewhere in between these hybrids, with clone 90 being most rot prone (and with the smallest yields) and 239 being least rot prone. Among the clones, 198 had the largest yield.
3. …And finally, tips to mull over during the dormant season for 2021 disease management
- Hill grafted vinifera to protect scion buds from severe winter cold and insure a supply of suckers for trunk renewal. I hope we never get a repeat of the 2014-2015 winter, at least not in my lifetime. But there is no guarantee of that. Many in PA (and other northeastern states) that did not hill before that winter, suffered tremendous losses. If we have another severe cold event this winter and grafts are not protected, you can develop crown gall at the graft and worse yet, the whole scion can die leaving you nothing with which to renew a dead trunk. Hilling will not prevent cold damage to the trunk and the crown gall that sweeps in after it, but it will save the scion just above the graft. A vine that you’ve toiled to cultivate for many years, and that has developed a deep, powerful root system, can become worthless if the scion is killed. Yes, there is the possibility of field grafting in case the scion dies, but that too can be laborious and costly, and requires a certain set of skills that may not be readily available.
- Continue to keep detailed records of where diseases were worst; those are the areas where disease are likely to show up first in 2021. If you had an easier time with downy mildew this year, remember that the pathogen can remain in your vineyard for several years in the form of tiny overwintering structures that ‘rest’ on the vineyard soil. As next spring rolls around, begin scouting for downy by mid to late May. The first downy mildew infections can occur during rainfall (at least 0.1 inches of rain and 50 °F) a few weeks prior to bloom, when vines have developed about 5-6 leaves per shoot. Keeping records on where downy tends to be most problematic in your vineyards, will help you to focus your early scouting efforts for more efficient and effective fungicide applications.
- Understand the pros and cons of the downy mildew fungicides. The old standards like mancozeb (Penncozeb, Manzate, Dithane, etc), Captan, and copper formulations are effective and are great for multiple, back to back applications because they pose little risk in terms of the development of resistance, but they are not as rain-fast as the newer materials like Revus, Ridomil, Phosphorous acids, and Zampro, and may need to be reapplied more often under heavy and frequent rainfall conditions. In the other hand, the newer fungicides should not be used more than two or three times per season, and even though the label may permit it, we recommend you don’t make back-to-back applications of the same chemistry, among these materials. That may be fine for one year. But as you know, we can get hit with high downy mildew pressure for several years in a row, and making back to back sprays of the same chemistry, for multiple years in a row, can burn that chemistry out faster. And speaking of resistance, downy mildew resistance to the strobilurins (FRAC 11, which also includes Reason fungicide) is common in the northeast and this class of fungicides should probably not be relied upon anymore for control of this disease in many parts of Pennsylvania where these products have been used intensively over the past 10-20 years. This is especially important when considering what to spray during the critical fruit protection period, from immediately before bloom to about 4 weeks after bloom.
- Cultural measures to apply this winter to reduce overwintering sources of inoculum. Cultural controls are generally not a substitute for seasonal fungicide sprays, but they can make your spray program more effective. To avoid reinventing the wheel, here are some tips from an earlier blog; “During dormant pruning, remove all clusters not harvested and as much diseased/dead/old wood from the trellis as is practical. Throw this material into the row middle and chop it up, or better yet remove it from the vineyard and burn it. This is especially effective against Phomopsis and black rot. Also, upright training systems (like vertical shoot position) reduce the probability that pathogen spores will be splashed upward from cordons and trunk, into the fruit zone during rain”.
by Kevin Martin, Business Management Extension Educator, Penn State Extension
Corona Virus Food Assistance Program 2.0 (CFAP 2) is live. This program was originally created to provide financial assistance to farms that were directly impacted by Corona virus. Early on, supply chains broke down and there was price volatility in certain crops. Some crops could not be harvested. CFAP was designed to reimburse those farms for some of their losses.
CFAP 2 is a different program altogether. Commodity based restrictions are no more. If a farmer is growing it, the farmer is getting paid something. All that is required is a simple application. This program has been live for two weeks.
To apply, contact your local Farm Service Agency (FSA) office. Some offices are open by appointment, but all can be contacted via phone. Applications need to be finalized by December 11, 2020. More information can be found at farmers.gov/cfap
This update is being provided now because I wanted to gather some specific information about grapes and cooperatives. For better or worse, payments will match 2019 sales. This means that payments will be based on certificates issued in 2019. It will not include certificates that matured in 2019.
To determine gross revenue before you contact FSA, have your schedule F ready. The grape payment would typically be calculated on gross sales of grapes that show up on lines 2, 3(a) and/or 8. Line 2 would typically include payments from cooperatives. Line 3 might include certificates or dividends. Line 8 sometimes includes cash payments for grapes where the buyer did not provide a 1099. This will vary based on software and accountant methodology. No accounting for expenses is necessary. This payment is based on gross sales, not net.
|2019 Sales Range||Percent Payment Factor|
|$0 to $49,999||10.60%|
|$50,000 to $99,999||$5,300 + 9.90%|
|$100,000 to $499,999||$9,250 + 9.70%|
|$500,000 to $999,999||$48,049 + 9.00%|
|Sales over $1 million||$105,800 + 8.80%|
As you can see, these payments are slightly graduated as gross sales go up, but only slightly. As specialty crop commodity growers profit comes through volume, paying based on a percentage of gross sales will dramatically increase profitability. In the best of times, profitability does not exceed 30%. This payment will represent somewhere between 30% and 100% (or more) of 2019 net income. In other words $6,000 for a typical hobbyist or $25,000 for a typical full-time grower.
Payments are capped at $250,000 per entity. Family farms with multiple active participant/owners can work around this cap. Needless to say, this is the direct subsidy program that a lot of growers have been looking for that I did not think we would ever see again. To be fair, that is the general theme of 2020.
Good luck. And happy harvesting and winemaking.
From the Vineyard (#1): Post-veraison berry shrivel and discoloration – symptoms, causes, and conditions
by Cain Hickey, Viticulture Extension Educator, Penn State Extension
This is the first of a series of blog posts called “From the Vineyard.” This series will highlight stakeholder reports and questions. If one or two growers have a similar report or question, it is possible that others may as well. The timing of the second post in this series will be dependent on feedback, reports, and questions we hear from stakeholders. In other words, there is no predetermined, “set” frequency for “From the Vineyard” posts.
In the last few weeks, three different growers have sent me pictures of shriveled and/or discolored grapes within clusters. Two growers noticed pink berries (sometimes accompanied by shriveling) with green rachis tissues in their Cabernet franc vineyards located in Lancaster County, PA. Another grower noticed shriveled berries with necrotic, brown rachis tissue in their Petit Verdot vineyard located in Chester County, PA. See the photos, below (thanks to these growers for sharing the photos and giving permission to post!)
When hearing about the observed symptoms over the phone, my immediate reaction was that “bunch stem necrosis” (BSN, also called “late season bunch stem necrosis”) was the issue in all cases. However, upon receiving photos and sharing them with Penn State Wine and Grape Team colleagues, I realized that BSN may have been the issue in only one of the cases. After doing a bit of research, it became evident that berries shrivel and become discolored after veraison due to different factors. The resources, below, collectively describe four different scenarios where berries may become shriveled and/or discolored after veraison: berry shrivel (also known as sugar accumulation disorder, SAD), dehydration, bunch stem necrosis, and sunburn. Note that sunburn in white-berried cultivars often manifests in skin browning, hardening, and cracking on the outside face of the cluster; the below resources show sunburn can result in pink berries in red-berried cultivars.
The goal of this post is not to reiterate the information provided in the above resources (but I would encourage everyone to review those resources). The goal is to diagnose the symptoms in the above photos so that growers can be aware of these issues, scout their own vineyards, and share future observations Based on the information provided in the above resources, my hypotheses are that the top photo of Cabernet franc is a function of SAD (sugar accumulation disorder, or “berry shrivel”), the middle photo of Cabernet franc is function of sunburn, and the bottom photo of Petit Verdot is due to BSN. Here are some additional observations that resulted in my diagnoses…
Differentiating SAD and sunburn. The grower that provided the top photo of Cabernet franc also said that the fruit tasted very tart and “wasn’t ripening” – low Brix is a hallmark of berry shrivel, or SAD. Further, in the top photo, the pink berry color appears to exist in berries throughout the clusters and there does not appear to be a pattern where only berries highly exposed to sunlight are pink – a pattern we would expect to see if the issue was sunburn (and as seen in the middle photo). The grower that provided the middle photo of Cabernet franc also said that Brix levels were similar between pink and purple berries – maintained, or increased, Brix is a hallmark of sunburn (see top two reference links, above).
Differentiating sunburn and BSN. Though the start to the growing season was cool and “slow” in PA, June through August was relatively dry, warm, and sunny. Verbal reports suggest that some vineyards in Chester County received greater rainfall than some vineyards in Lancaster County. Based on my knowledge of the sites, it is likely that the Petit Verdot vineyard in Chester County has greater water holding capacity (relatively flat; high organic matter and clay content) than the Cabernet franc (middle photo) vineyard in Lancaster County (sloped, convex landform). Anecdotally, sunburn occurs more often under hot and dry conditions where water may be limiting (e.g. Lancaster County vineyard) whereas BSN has been linked to excessive water availability during and after veraison (e.g. Chester County vineyard). A symptomatic difference between BSN and other conditions that cause berry shrivel/discoloration is that the rachis tissue becomes dried and necrotic with BSN (see Petit Verdot photo) whereas rachis tissue remains green with the other conditions (see top two photos of Cabernet franc).
What does this mean practically? This is more just an “FYI” in case you have wondered about the cause or condition of similar symptoms in your vineyard. It is prudent to collect as much data as possible to identify causes of your own vineyard symptoms. Using a different example unrelated to berry shrivel… are those red canopy leaves due to nutrient imbalances or systemic disease? Observing the patterns of red canopy leaves throughout the vineyard and their relation (or lack thereof) to vineyard topography and soil type can aid in determining the cause of red canopy leaves. Nutrient imbalances are often seen where the land is highly convex and sloped (e.g. where “lean,” rocky soils exist). However, lab tests with vine tissues can objectively determine the cause, which may be an imbalance in potassium or magnesium, or the systemic disease known as “red blotch” (or possibly something else altogether).
Please note that the above diagnoses are only hypotheses; I documented my reasoning for these hypotheses based on the photos, grower feedback, and knowledge of weather patterns and sites. Also note that the above-mentioned berry shrivel conditions are not caused by pathogens (to our knowledge). Thus, spraying a fungicide will not manage these issues. In fact, since little is known about the cause of BSN and SAD, there are limited management recommendations for their control. Below is some further discussion regarding sunburn and BSN.
Sunburn. From the perspective of reducing sunburn, the obvious answer is to be judicious with leaf removal magnitude. However, since rot management is of utmost importance in our climate, refraining from fruit zone leaf removal altogether is unlikely a viable option for vinifera production, particularly in many rot-sensitive cultivars that are popularly grown in PA (e.g. Gruner Veltliner, Pinot gris, Pinot noir, Riesling, Sauvignon blanc).
Our research has shown that fruit zone leaf removal to the point where all clusters are completely exposed can increase wine quality potential and reduce bunch rot in Bordeaux reds; however, leaf removal to lesser extents (where an average of one to two fruit zone leaf layers exists around the clusters) has also been shown to improve wine quality potential and rot management. Thus, considering the constraints of time and labor resources, it would seam that fruit zone leaf removal to an average of one to two fruit zone leaf layers may be a commercially viable option to achieve a balance between wine quality, rot management, and sunburn avoidance. Removing two to three fruit zone leaves per shoot can produce an average of one to two fruit zone leaf layers; removing four leaves per shoot produces a fruit zone that is generally devoid of leaves (see photos, below).
We need to gain a better understanding of how the combination of leaf removal magnitude and timing effects sunburn development in both red- and white-berried cultivars. Our observations suggest that sunburn is minimized when leaves are removed early in the season (e.g. at BB-sized berries or earlier). However, we have observed sunburn on the external-facing side of clusters, regardless of when leaves were removed; this was especially observed in white-berried cultivars. Weather patterns complicate the issue (they always do with field experiments) and will likely result in difficulty in drawing concrete conclusions for optimal leaf removal practice to abate sunburn development.
Bunch stem necrosis (BSN). From the perspective of reducing BSN, we first must become more familiar with the causes of this disorder. The above resources mention that excessive water availability near and after veraison likely increases the development of BSN. Since we cannot control the weather, proactive decisions to reduce water status (e.g. planting on sites that have less clay, are sloped and well-drained; installing drain tile) may reduce the incidence of BSN. When I was working in Virginia, anecdotal observations suggested that Cabernet Sauvignon vines of lower vigor and water status (grown within root restriction bags) had less BSN than vines of greater vigor and water status (grown without root restriction). In time, we will hopefully become more familiar with the exact causes of BSN so we can refine recommendations to avoid its development.
I hope that many growers are not observing berry shrivel or discoloration in their vineyards. My hope is that many have benefitted from the recent dry weather patterns experienced across the state and that harvest is off to a great start. In general, reports suggest that harvest of white-berried cultivars is well underway and may be coming to an end in the coming week or so. Pinot noir is a red-berried cultivar that has likely been harvested in many instances; some reds have also likely been harvested for sparkling or rose wine production. Harvest of other red-berried cultivars for red wine will likely commence this week and next.
My very best to all PA growers and winemakers for continued success in the 2020 vintage!
The Penn State Grape and Wine Extension Group is asking you to contribute to a Pennsylvania Grape Price Benchmarking tool.
We developed this survey because of feedback we have received about the lack of grape price transparency in Pennsylvania. This is a preliminary effort to future, in depth industry surveys that will provide information about grape and wine production and pricing trends across the Pennsylvania grape and wine industry.
You are asked to answer questions about the grape varieties you grow and/or buy, production volume, and the price per ton received/paid. Please feel free to fill out this survey multiple times as you sell additional crop throughout the season.
We will report results from the survey in the Penn State V&E Newsletter. If you do not receive the Penn State V&E Newsletter you can subscribe by sending a blank message to: WINEGRAPE-L-SUBSCRIBE-REQUEST@LISTS.PSU.EDU
Please be assured that your responses are completely confidential. We will only report weighted average prices, and minimum and maximum prices per ton by variety received so that no individual’s answers will ever be identified.
You can access the survey here: https://pennstate.qualtrics.com/jfe/form/SV_9TRRzvnzUEmfWM5
by Cain Hickey, Viticulture Extension Educator, The Pennsylvania State University
Harvest is an exciting part of the season. It is the culmination of the long growing season. The harvested crop is taken into “safer” realms in tanks, bins, and barrels to eventually produce wines that will be enjoyed. Harvest is also a stressful time of the season. Schedules change several times and logistics need adjusted accordingly. The reward from the last five or six months of hard work (not counting dormant pruning) is at stake. And, among other variables that will be further discussed below, the outcome of harvest is dependent on weather patterns which are out of our control. Such is the life of farming and, in our case, growing grapes. But it is worth it. And, grape growing challenges are not unique to Pennsylvania and humid growing regions in the US; grape growing and harvest challenges abound in growing regions worldwide, from the western US to New Zealand, to European countries, and regions in between.
Harvest decisions are the result of knowledge that is applied to the unique combination of cultivars and growing conditions of each vintage.
“Harvest” is a timely topic in Pennsylvania. From now through the end of October, grapes will be harvested and processed into wine throughout the Commonwealth. Some grapes may even be harvested into November and beyond in regions where ice wine or “late harvest” production is a goal. After Dr. Molly Kelly and Dr. Gill Giese presented their “A Balanced Harvest” webinar (https://bit.ly/32ohHPR), I was inspired to try and document several considerations that go into harvest decisions. And not necessarily doing so by citing literature. But, rather, by summarizing and reflecting on what I have learned from being involved in viticulture research, education, and extension and working with members of the eastern US wine industry over the past decade. I will paraphrase previous experiences and conversations with growers. And try to make points through the use of fictional case studies to exemplify circumstances that may be encountered in commercial vineyards.
Do we have an extensive enough literature base to cite how the combination of site, cultivar, management decisions, post-veraison weather patterns, and primary and secondary metabolites manifest in the resultant wine? We do have pieces of this story. For example, in humid growing regions, we generally understand that exposed grapes have potential to have less rot, lower acidity, and greater aroma and color development relative to shaded fruit. However, it would be a lofty goal to write a review on all the factors that can affect wine quality potential and thus dictate harvest decisions. Conclusions from such a review would be highly speculative in order to account for the multitude of variables that influence harvest decisions. Further, it would be difficult to apply any conclusions across the unique terroirs in grape growing regions, even just in the “humid growing regions of the US” which encompasses southeastern, midwestern, mid-Atlantic, and northeastern US states. Harvest decisions can be nebulous and are difficult to research and draw conclusions from unless “harvest date” is a factor in the experimental design. There are scenarios that limit the ability to make an objective statement about harvest decisions. Take, for example the recent and highly divergent weather patterns throughout the post-veraison periods of 2018 and 2019. All other variables standardized, these vintages will likely result in different wines.
To further make a case that harvest and related decisions are difficult subjects for objective statements, let’s consider whether the vineyard or cellar is more impactful for determining harvest. Is harvest a viticulture-based or enology-based decision? The answer: “yes” (as in, “both”… but with a weak attempt at humor). As a viticulturist, I am biased. I could argue the harvest of grapes is only possible because of the vineyard and its judicious management in the current and previous seasons. Which is true. However, I know that Molly Kelly, Penn State Enology Extension Educator, would justifiably argue that we harvest grapes with winemaking goals in mind. Which is also true. And I know that, in commercial situations, harvest date is often a mutual decision between the vineyard manager and winemaker; sometimes one person occupies both roles and, in other situations, the vineyard manager and winemaker work together to decide the optimal harvest date. I am not sure if the decision is easier to make as an individual or as a collaborative decision… this opens up psychological debate which goes far beyond my expertise. I’d ask enologists and winemakers to be forgiving of the text written herein, as it may be biased toward the vineyard and I may show ignorance about many important enological considerations for harvest decisions.
Harvest decisions are a consequence of several factors, some predictable and many not, that are unique to each commercial situation.
Harvest decisions are a consequence of experience, theoretical knowledge, seasonal vineyard management practices, and numerical and sensory-based measurements that are put into action under the constraints of site, cultivar, post-veraison weather patterns, labor availability, stylistic winemaking goals, vineyard acreage and winery tank space, and current inventory of wines. Read that previous sentence again; it is a lot. And, while thorough, it still falls short of exhausting the number of potential factors that may impact harvest decisions. So, what can we predict for sure about harvest decisions and timing in Pennsylvania? With rare exception (site limitation, vintage effect, wine stylistic goal), Chardonnay will be harvested before Petit Verdot. And, most grapes will be harvested between late August and late October. These are the limited number of “predictable outcomes”. “Unpredictable outcomes” may become more predictable with an increase in breadth of knowledge and experience, especially with the same cultivars grown on the same site. I wish there were more objective statements that could be made about ideal harvest decisions and parameters. But, “ideal” is dependent on several factors, including those words/phrases that are emboldened/italicized above. To read more about how each emboldened and italicized word/phrase from the first sentence of this paragraph may impact harvest decisions, see this file (I kept this text separate so as to reduce the length of this blog post):
Practical vs. abstract approaches to harvest.
Note that the use of the terms “practical” and “abstract” is not meant to impose partiality to one approach or the other, nor to suggest that approaches to harvest only exist in these two forms or only in contrasting extremes. But rather to highlight how harvest decisions can be vastly different and dependent on values and goals. The practical-minded grower may error on the “safe side” by picking early to get rot-free fruit in the winery that also may have a lower pH and is likely to be microbially stable; the “risk” here may be picking fruit at less than optimal maturity for a targeted wine style. In contrast, the abstract-minded grower may error on the “riskier side” by picking based on sensory observations to make wine with fruit at peak maturity; the “risk” in this case may be that fruit rot and pH have increased as a consequence of “extended hang time”. Can one be practical and achieve optimal fruit maturity? Absolutely; theory and practice can come together in the real world. And, “optimal fruit maturity” is highly subjective and dependent on winemaking style goals. However, the combination of variables mentioned above (site, cultivar, post-veraison weather patterns) will affect the chances of theory and practice coming together in the form of rot-free fruit that has balanced chemistry and flavors such that little amelioration of the must is necessary before fermentation commences. The more odds that are against us (lack of experience, poor vineyard management, poor cultivar match with site, adverse weather patterns, labor scarcity, etc.), the more difficult it will be to achieve targeted wine styles, regardless if one is more abstract- or practical-minded. Most stakeholders likely have a balance of practical and abstract approaches to harvest in an attempt to achieve fiscal sustainability (e.g. by avoiding extreme bunch rot and crop loss) and to produce wines with recognition that round out the offerings of various wine styles in the tasting room. Winemaking “intervention” is necessary when harvested fruit is over-ripe, under-ripe, or falls short of the ability to achieve the intended wine style.
Harvest decisions are complex and sometimes difficult. And justifiably so – lots is at stake. You want the best possible outcome (balanced, pleasant wines) from the crop you have worked hard to cultivate and maintain free from diseases and other pests all season long. Aim for the greatest quality each vintage. The successful approach to achieving quality starts during the dormant and growing season by practicing good viticulture. Use every advantage you have to make judicious harvest decisions. Be able to predict your harvest schedule but allow for some flexibility and be prepared to change plans as circumstances change. There are constraints in every vintage. As the number of adverse situations (rainfall, bunch rot, poorly drained site, suboptimal vineyard management) increase, there is greater need to take a pragmatic approach to harvest. Be practical in dealing with constraints to make the best harvest decisions possible; this requires the use of past experiences, knowledge of viticulture and enology theory, and an understanding of how current season viticulture management, weather patterns, and numerical and sensory observations will impact crop quality and the ability to achieve your targeted wine style. Acknowledge limitations of your cultivars grown on your site and be prepared to be responsive to the weather patterns of the immediate past and future.
The Winemakers Research Exchange, funded by The Virginia Wine Board, has published a newsletter with several Harvest Reminders. You can access this newsletter by clicking here: http://www.winemakersresearchexchange.com/august-2020-harvest-reminders-1
Hopes for a great 2020 vintage.
My sincere best wishes to all for a wonderful 2020 harvest! May the weather be dry with just enough intermittent rainfall to keep canopies photosynthetically active yet limit downy mildew and rot development.
All the best to each of you!
On August 12, 2020, Dr. Bruce Bordelon, Professor of Small Fruits and Viticulture at Purdue University, presented “Fundamentals of Herbicide Drift in Vineyards” as part of the PSU Wine and Grape Team’s Weekly Webinar Series.
Bruce discussed several aspects of herbicide drift in vineyards, including causative chemicals, detrimental weather patterns that exacerbate chemical drift and volatility, common vine herbicide injury symptoms, differences in cultivar susceptibility to herbicide injury, and productive actions after herbicide injury has been identified in the vineyard. Bruce was kind enough to provide his presentation for reference. The link to the presentation can be found here:
All the best to everyone for dry weather throughout harvest of the 2020 vintage!
On Wednesday, August 19, 2020, Molly Kelly, Enology Extension Educator, Penn State Extension, and Gill Giese, Assistant Professor and Extension Viticulture Specialist, New Mexico State University presented A Balanced Harvest live webinar.
Gill Giese covered applied physiology of grape maturation; vineyard factors that impact grape ripening; relating vineyard to winery (grapes to wine); practical aspects of harvest.
Molly Kelly introduced BSA (berry sensory assessment), a codified system of describing grape composition, providing a common language of grape ripening and grape maturity assessment.
Please see links to both presentations below, including a written transcript.
By Molly Kelly, Enology Extension Educator
The Preharvest Planning and Winery Sanitation webinar from July 29th, 2020 is summarized below.
Harvest is fast approaching, ready or not. With some careful planning, harvest does not have to be chaotic. Now is the time to go back and look at the 2019 harvest and identify areas needing improvement. You should also have a plan for each lot of grapes and have responsibilities for each employee clearly defined.
Now is also a good time to inspect the winery. Clean up clutter and determine what needs replaced. Resolve any pest issues and check the refrigeration system. Is the water quality adequate? If not get it serviced now. For worker safety, install CO2 sensors if you do not have them already.
If you are purchasing fruit, have all contracts in place. Have the grower provide a crop estimate so that you can plan accordingly. Request berry parameters (Brix, pH, TA) be sent regularly as harvest approaches. Also confirm if the fruit will be delivered to your winery or picked up. Visit the vineyard regularly and be sure to convey expectations. Examine all fruit for ripeness and any rot or insects present.
In preparation for crush, consider three main areas: the crush pad, fermentation cellar and barrel room. Within each of these areas, pre-crush tasks can be divided into four areas: planning, corrective maintenance, preventative maintenance and lastly sanitation. Of this list, sanitation is definitely of high importance.
While planning, consider a baseline work-flow for receiving, crushing, pressing and fermenting the grapes. Start with a basic white and a basic red plan. You can add more details as harvest goes on. This also allows new employees or harvest interns to know what to expect next in the process. I also recommend a HACCP plan (Hazard Analysis and Critical Control Points). This involves looking at the production process from start to finish. This can be in a flow-chart format. You then identify where hazards can occur and put in controls and monitor them routinely. For example, at the end of fermentation measure the volatile acidity, have an acceptable level, list how to address if too high. Continue to monitor throughout the winemaking process and keep good records.
Make sure to know approximate harvest yields and determine the tank/barrel capacity needed. For whites you will need 210 gallons of tank space per ton of fruit. Red fermentations on the skins will need 250 gallons per ton. Storage gallons for both will be approximately 165 gallons per ton.
In the winery, have your cooling system checked, inventory barrels and identify leakers. All equipment should be tested including scales, crusher/destemmer, pumps, press, and forklift several weeks before harvest. Remember to inventory all wine. What do you still have an abundance of in inventory? Maybe it is time to re-evaluate plans to produce those wines this harvest.
On the crush pad, make sure that bins are cleaned. Know where grapes will be stored, if needed, when they arrive. Do you need to arrange for a refrigerated truck rental? In addition, have a plan for how pomace will be disposed. It is imperative that pomace be as far away from the winery as possible. You will certainly have a fruit fly infestation if it is close to the winery.
This is by no means a complete list but please refer to the list below of common chemicals and supplies that you may need.
- Sulfur dioxide (potassium metabisulfite)
- Acids (tartaric, citric)
- Rice and yeast hulls
- Gas cylinders
- ML culture
- Yeast nutrients
- Diammonium phosphate or other N source
- Fining agents (bentonite, isinglass, PVPP)
- Filter pads (stacked pad, sterile cartridge)
- Cleaning supplies
Don’t forget to order lab supplies if you will be performing tests in-house. If you will be sending samples to a reference lab, have enough sample containers, labels and shipping boxes on hand. Some basic things that you may be measuring include:
- pH-replace probe every 2 years or as needed
- Brix-have extra hydrometers on hand
Some additional equipment considerations:
- Check all equipment is in functioning order and service if needed
- Do you need to rent an extra forklift?
- Do you have an extra pump/press on hand?
- I recommend going through a dry run to ensure that you haven’t missed anything
- Clean and sanitize everything
- Know your neighbors. Can you ask to borrow supplies if needed?
- Have spare parts on hand for minor repairs
Consider staffing needs. Have standard operating procedures (SOPs) for everything to make sure that each protocol is being done exactly the same by all employees and provide necessary training. Have personal protective equipment (PPE) on hand to provide a safe work environment. Material safety data sheets (MSDS) should be available for every chemical in the winery. Information contained in the MSDS includes precautions to be taken when using a chemical and what to do in case of exposure.
With the current coronavirus pandemic, make sure to comply with all state and federal regulations. Check the CDC guidelines for manufacturing workers (includes food processing facilities) and PA guidance for businesses for the most up-to-date COVID information. Be sure to train all employees in COVID regulations and safety training. You probably have many of these in place for tasting rooms.
Proper winery sanitation is absolutely the most important aspect in quality wine production. Wine is an acid food (low pH). This combined with the ethanol that it contains makes wine unable to support the growth of human pathogens. According to the Federal Drug Administration (FDA), a winery is a food processing facility and subject to federal regulations, especially Good Manufacturing Practices (GMPs) listed in Title 21 CFR 110.These regulations include sanitation and processing requirements for the production of safe food.
First, we will introduce some definitions used in a sanitation program: cleaning, sanitizing and sterilizing. Knowing the differences among these will enable a winery to implement a more effective sanitation plan.
Cleaning: Removing of mineral of organic matter, and debris from surfaces (normally using detergents). This step also eliminates environments conducive to growth of spoilage organisms.
Sanitizing: Reduction of the microbial population to a safe or acceptable level (kills 99.99%) of organisms. NOTE: You cannot sanitize a dirty surface!
Sterilizing: Provides 100% kill of viable cells including spores.
General steps in cleaning and sanitizing include:
- Removal of debris without water. This may include removal of rachises and leaves from the crusher/destemmer missed last year.
- Pre-rinse to remove some organic debris that is not tightly bound.
- Use of detergent, usually alkaline in nature. This will remove organic material such as proteins.
- Use of a sanitizer, usually acidic in nature. This will remove inorganic matter such as metallic residues and alkaline residues not removed during cleaning with detergent.
- Rinse (may not be needed with certain sanitizers)
Some areas/sources that are prone to build-up of spoilage organisms include:
- The vineyard: fruit may come in from the vineyard with rot or insects
- Diluted pools of juice on the crush pad or in the winery
- Second-hand barrels: know your source
- Imported bulk wine
- Areas of the winery that are difficult to reach
- Fruit flies: capable of carrying spoilage organisms throughout the winery
- Wine thief: sanitize or sterilize between each barrel using 70% alcohol. A presentation from Cornell included the suggestion that a thermos with >185F water would result in an instant kill of organisms when thief was dipped between barrels.
There are a number of factors involved in determining how likely it is for spoilage organisms to thrive including:
- Oxygen: acetic acid bacteria and others grow best in the presence of oxygen
- Temperature: the warmer the temperature (to a certain point) encourage organisms to grow. Lower temperatures inhibit their growth.
- Alcohol: the higher the alcohol, the greater the inhibition of organisms
- Molecular SO2: this is the free form of SO2 that is the antimicrobial form
- pH: the lower the pH the less chance of microbial growth. As pH approaches 4.0, the greater the chance of microbial growth.
- Nutrient status: if there is a nutrient source present, other spoilage organisms can grow
Some of the microbes that may grow during fermentation include non-Saccharomyces yeasts, lactic acid bacteria and acetic acid bacteria. In order to detect the presence of these organisms, you should monitor for the following:
- Ethyl acetate
- Spontaneous or sluggish fermentation
- Spontaneous malolactic fermentation
- Volatile acidity
- 4-ethyl phenol and 4-ethyl guaiacol
- Sulfur-like off odors
- Other off odors
As a rule of thumb, acid cleaners dissolve alkaline soils (minerals). Alkaline cleaners dissolve acidic soils and food wastes (proteins). The improper use of detergents can actually “set” soils, making them more difficult to remove (e.g. acid cleaners can precipitate proteins).
It is a common misconception that “if a little is good, more is better”. Using sanitizer concentrations above recommendations does not make sanitizer perform better. In fact, this can corrode equipment. Always follow manufacturer label instructions.
Prior to using detergents to clean, apply a warm (100-109F), high pressure rinse (600-1200 psi). Avoid the use of hot water that can “bake on” debris. Once the visible debris is removed, detergents are used to solubilize remaining deposits. Detergents include alkalies, acids, surfactants and rinses.
Alkalies are excellent detergents and include caustic soda (NaOH) and caustic potash in the pH range of 12.0 to 14.0. They work well on tartrates and have strong antimicrobial properties. Care must be taken when using them including the use of proper personal protective equipment (PPE). If used too concentrated, they will corrode stainless steel. There are milder alternatives such as sodium carbonate (soda ash) or trisodium phosphate (TSP) in the pH range of 10.0-11.5. The alkaline compounds kill cells by stripping the cell membrane of yeast and bacteria.
Acid detergents reduce mineral deposits and also soften water. The pH is between 1.5 and 3.5. These can also be corrosive to metals such as stainless steel. An example is phosphoric acid.
Surfactants lower the surface tension between a liquid (water containing detergent) and a solid (debris) making the dirt more soluble and easier to remove. One end of the surfactant is hydrophilic (water-loving) and the other end hydrophobic (water-repelling).
After cleaning with detergents, a rinse may be required. For example, a mild acid rinse (citric) can be used to neutralize alkaline residues.
Once thoroughly clean, a surface can then be sanitized. Sanitizers work by lysing cell membranes, blocking membrane functions (e.g. waste removal) and inactivating key enzymes. There are some combined cleaner/sanitizers but a sanitation step is still required. It is vital to make sure the surface is clean since sanitizers will preferentially bind to organic matter.
Some examples are listed below and their use briefly discussed:
- Acidulated sulfur dioxide
- Quaternary ammonium compounds (QUATS)
- Hot water and steam
- Peracetic/hydrogen peroxide
- Ethanol (70%)/80 proof vodka
Acidulated sulfur dioxide
This sanitizer has antimicrobial activity which is pH dependent (3.0-4.0). In acidulated cold water (pH below 3.5) more SO2 will be in the molecular form. Use 100 ppm SO2 (200 ppm potassium metabisulfite and 3 g/L citric acid, or enough to achieve a pH below 3.5). It is good for sanitizing hoses and in closed systems.
Chlorine-containing (sodium and calcium hypochlorite) compounds are halogens and are not recommended except for out of control microbial situations. They act as precursors in the microbial formation of trichloroanisoles (TCA). Chlorine dioxide is a broad-spectrum antimicrobial and is effective in destroying biofilms. Chlorine is not a by-product therefore TCA is not a concern.
The iodophors also have a broad spectrum of activity against microorganisms. At a concentration of 25 ppm, pH<4.0 it is active against bacteria, viruses, yeasts and molds. Iodine can be used to sanitize bottling lines followed by a cold rinse. There may be the potential for formation of TCA.
Quaternary ammonium compounds (QUATS)
QUATS are a cationic (positively charged) surfactant. At a concentration of 200 ppm they damage cell membranes of microorganisms (lactic acid bacteria more so than acetic acid bacteria). They leave a residual antimicrobial film if unrinsed. They can be used on floors and walls and other non-product contact areas.
Hot water and Steam
Hot water and steam are strong antimicrobials at >180F for no less than 20 minutes. They may degrade gaskets but are non-corrosive. Their main use is the sterilization of bottling lines and for barrel sanitation (140-176F using high pressure). At temperatures between 170F and 185F, there is an instant kill of microorganisms.
Hydrogen peroxide breaks down to superoxide oxygen (O2–). Peroxides are very effective antimicrobials but less so against spores and wild yeasts. Peroxyacetic acid (PAA) combines peracetic acid and hydrogen peroxide that work synergistically to kill 99.99% of microbes. At the diluted concentrations (2.5-15%) it leaves low residual PAA (3-5 ppm), requiring no rinse. A strong oxidizer, PAA can be used to sanitize many surfaces including barrels and bottling line sanitation. Concentrated solutions are corrosive, but diluted, it is also environmentally friendly, breaking down to acetic acid, water and oxygen.
Percarbonates and Soda ash (sodium carbonate)
Per(oxy)carbonates are a stabilized powder with hydrogen peroxide. Oxygen radicals are released via hydrogen peroxide. This alkaline product degrades to soda ash, water and oxygen. It is commonly used on barrels but, due to their porous nature, 100% kill is not achieved.
Soda ash is a strong alkaline compound. It dissolves proteins, fats, oils and carbohydrates. It also works well on tartrates. It can also neutralize odors associated with volatile acidity.
Ozone is a potent sanitizer but is not a cleaner. It is a hyper-radical of oxygen that has strong oxidizing properties. It can be dissolved in water or applied as a gas. It has a shorter half-life in water (seconds) compared to gas (24 hours). If water is used, it must be generated on demand by exposing a stream of dry air to an electrical discharge. It is active against bacteria, fungi and spores. Be sure to check gasket compatibility as ozone can degrade certain ones. Ozone is a strong irritant so train staff and have proper safety monitors in place.
For barrels, the following protocol is suggested:
- Perform high pressure cold wash
- Follow with hot water or steam
- Cool rinse 2-3 minutes
- Rinse with ozonated water (filtered water since minerals limit ozone effectiveness)
- Follow manufacturer’s suggested contact time/concentration
Additional sanitizing options include:
- UV light
- Dry ice blasting for barrels
- High power ultrasound for barrels
Hoses, valves and fittings
When sanitizing fittings, consider soaking in a solution. For example, an alkaline cleaner followed by a citric acid rinse to neutralize. Then apply acidulated sulfur dioxide to sanitize.
Tygon® corrugated hoses (you can see through them) are recommended. Rubber/fiber blend hoses are harder to clean and not transparent. Consider the use of foam balls to better clean hoses.
Ball valves tend to harbor more debris and microbial growth compared to butterfly valves. Take all valves apart and clean/sanitize prior to harvest. I suggest filling the tank with water when valves are replaced to make sure they don’t leak. Gaskets may need to be replaced and can be easily made with a gasket kit (use food grade rubber).
Drains and Filters
Drains can be plugged and filled with sanitizer or hot water. I have found that peroxycarbonates followed by a citric rinse to also work well.
If you choose to reuse filters, you can use a caustic/acid treatment followed by a sanitizing step. Rinse with a sanitizer before use (e.g. KMS/citric). Remember to perform an integrity test (e.g. bubble point) prior to filter use.
Care must be taken when treating barrels as chemicals can either taint the wood or extract essence.
Some considerations for barrels:
- Don’t let them dry out
- Store with KMS/citric acid solution
- Clean the outside as well as the inside
- Recover with a percarbonate based cleaner (1 T/gal), let sit 24 hrs., rinse, rinse again with citric acid (0.5 t/gal)
Cleaners and sanitizers should be rotated every 1-2 weeks. For example, four days a week use a caustic detergent to clean (alkaline) followed by peroxyacetic acid sanitizer. The fifth day, use an acid cleaner to decrease mineral deposits. This will also remove deposits not removed by the alkaline cleaner. Then apply an appropriate sanitizer.
Some microbes use nutrients from juice and wine to form polymers. Once on a surface, other bacteria will aggregate and attach. They continue to grow, forming a biofilm with a protective layer surrounding the microbes. Invisible to the naked eye, biofilms are resistant to many chemical cleaners. They usually need physical action (scrubbing, high pressure) for removal.
One suggested treatment is the use of caustics (167F for 30 min.) followed by a citric acid rinse. Ozone has been shown to be ineffective in treating biofilms.
In the winery, we typically do not achieve true sterility. Rather, we reserve “sterilization” steps for processes such as sterilization of the bottling line.
Hot water and steam are normally used:
- 180F for 20-30 min.
- Ozone for 20-30 min.
Sources of contamination at bottling include:
- Filler bowls: use steam or hot water (180-185F) to “sterilize”
- Thermal dots on the outside of filler bowl can verify temperature
- Mist filler spouts with 70% ethanol to inhibit microbial growth
- Corker: likely to have spilled wine present. Mist jaws with ethanol during bottling.
- Activity: limit number of people in the area
- Strips are available to test concentration of sanitizers
- Verify contact time by using a timer
- Verify proper temperature of solutions
- Areas of the winery can be swabbed and plated on agar growth media or sent to a reference lab for culture and/or molecular testing
- Photodetectors using bioluminescence technology can be used to monitor presence of cellular material. Surfaces are swabbed and if ATP is present (energy-carrying molecule found in all living things), in the presence of luciferin and an enzyme, it will fluoresce. The degree of fluorescence is proportional to the number of cells present.
- Clean then sanitize everything prior to use
- Clean everything after use
- Keep the winery premises clean and clutter-free
- Monitor for mold, bacteria, rodents etc.
- Deal with pomace immediately
Remember that winery sanitation will impact final wine quality. Clean, then sanitize!
- Butzke, C., Barrel Maintenance, Dept. of Food Science, Purdue University, 2007.
- Crowe, A. Avoiding Stuck Ferments, Wine Business Monthly, August 2007.
- Dharmadhikari, Murli. “Harvest Preparation.” Vineyard & Vintage View 6, no. 7 (1991): 1.
- Howe, P., ETS Laboratories, SOWI “Current Issues” Workshops March 2011.
- Just, E. and H. Regnery. Microbiology and Wine Preventive care and monitoring in the wine industry. Sartorius Stedim Biotech. 2008.
- Lansing, R. May 2011. Managing Bottling Operations. Wine Business Monthly.
- Margalit, Y., Winery Technology and Operations, The Wine Appreciation Guild, San Francisco, 1996.
- Menke, S., Cleansers and Sanitizers, Penn State Enology Extension, 2007.
- Neradt, F. 1982. Sources of reinfections during cold-sterile bottling of wine. Am. J. Enol. Vitic. Vol. 33. no. 3.
- Pregler, B. Dec 2009. What’s Cool: Accurate Membrane Filter Integrity Testing. Wine Business Monthly.
- Ritchie, G., Napa Valley College, VWT 280, Cellar Hygiene, 2007.
- Tracy, R. and Skaalen, B. Jan/Feb 2009. Bottling-last line of microbial defense. Practical Winery and Vineyard.
- Van de Water, L., Practical Winery and Vineyard Journal, Sept/Oct 2009.
- Worobo, R. June 2012 Northern Grapes Project Webinar “Introduction to Winery Sanitation: Options to Applications.
- Zoecklein, B. et al, Wine Analysis and Production, Aspen Publishers, 1999.
- Zoecklein, B., HACCP-Like Plans, Enology Notes #115, Virginia Tech, August 2006.
by Molly Kelly, Enology Extension Educator
By managing fermentation, winemakers today have many options to enhance the varietal characteristics of their wines, and to express regional attributes. Winemakers know that temperature is a management tool that affects the rate of fermentation; similarly, the presence of grape solids enhance yeast survival. Very importantly, adequate nitrogen (N) is necessary for a successful fermentation.
Grapes contain a variety of nitrogenous compounds, the sum of which may be affected by viticultural practices. For instance, research has demonstrated that N concentration is 2X greater with application of foliar N and appropriate irrigation use than without foliar N and irrigation. Other research suggests that N application around veraison appears to be an effective way increasing N in the fruit, regardless of water-supply status of the vines. The concentration of nutrients, whether too great or too little, can induce stress and lead to different concentrations of flavor compounds. For instance, H2S formation is a well-known example related to inadequate nutrients leading to nitrogen depletion stress.
A common practice among winemakers is to make a standard addition of diammonium phosphate (DAP), or other N source, to the juice or must (100-300 mg/L) at inoculation without measuring the nitrogen concentration. The objective of this article is to show that N addition has significant flavor (and ultimately, economic) consequences and that measuring the initial nitrogen concentration provides the opportunity to adjust N addition – not only to achieve an adequate fermentation rate, but also to more reliably guide the flavor profile and style of wine intended.
Definition and Measurement of “YAN”
Grapes contain a variety of nitrogenous compounds of which the most important are the primary (alpha) amino acids, ammonium ions, and small peptides. These three nitrogenous compounds – amino acids (excluding proline), ammonium ions, and small peptides – constitute what is commonly referred to as yeast assimilable nitrogen (YAN) or fermentable nitrogen.
YAN measurements, ideally, should be performed directly on juice or must samples at the point of inoculation to avoid over-estimation due to processing losses which inevitably occur between vineyard and the fermenter. Juice samples taken from grape musts can under-estimate total berry YAN due to the disproportionate concentration of amino acids contained in the unsampled grape skins. While an early warning for low YAN may be obtained by sampling in the vineyard one to two weeks prior to harvest, measurement immediately before fermentation is necessary due to the highly variable nature of YAN measurements during those last weeks before harvest.
Favored methods of measurement of YAN are (a) enzymatic assay kits, (b) the method known as the Formol Titration, which consists of neutralizing a juice sample with a base, then adding an excess of neutralized formaldehyde, and re-titrating the resulting solution to an endpoint; and (c) use of expensive equipment such as the HPLC (high-performance liquid chromatography). Typically, wineries use the first two methods; commercial labs may use the third method.
How much YAN
YAN has the most impact on fermentation speed compared to other compounds. It impacts yeast biomass at the beginning of fermentation and sugar transport during fermentation. At the end of growth phase, N is depleted resulting in decreased protein synthesis and sugar transport. A YAN addition at this point reactivates protein synthesis and sugar transport increasing the fermentation rate. Oxygen is rapidly consumed in the beginning of fermentation. Decreased oxygen inhibits sterols and fatty acid synthesis by yeast. This causes decreased yeast growth and viability at the end of fermentation.
Sterols and fatty acids are survival factors needed for the yeast cell membrane to function. As ethanol increases, hydrogen ions accumulate in cell requiring more energy to expel them. The pH decreases inside the cell causing cell death. Oxygen adds at end of growth phase increase sterol production. Therefore, microoxygenation and pump overs would be beneficial at 1/3 of the way through alcoholic fermentation (end of yeast growth phase).
The manner in which N is assimilated by yeast depends on the source. Organic N (amino acids) is actively transported into the yeast cell. Through additional reactions N is incorporated into glutamine and glutamate and eventually used in the synthesis of other amino acids and nitrogenous compounds. This process is gradual and efficient compared to inorganic sources. Ammonium nitrogen (inorganic N) is consumed quickly and is less beneficial. Amino acid mixtures vs single N sources are more efficient because the yeast directly incorporates the amino acids into proteins rather than having to synthesize them.
Ammonia, which exists as ammonium (NH4+) ions in must, is used by yeasts prior to amino acids. The presence of NH4+ delays timing and uptake of amino acids by yeast.
The timing of N supplements and form of supplement will impact fermentation and volatiles. Types of N supplements include Diammonium phosphate (DAP), proprietary blends of DAP and amino acids (e.g. Superfood®, Fermaid K®, Actiferm) and balanced nutritional formulas containing inorganic N (e.g. Fermaid O®), organic N, sterols, yeast cell walls, fatty acids, yeast autolysis products and others. DAP is best used with low N musts. Other balanced nutrients should be added as well. At a rate of 100 mg/L DAP, 20 mg/L YAN is added.
It is common practice for winemakers to make N additions at the following times:
- Yeast rehydration to rebuild cell walls (rehydration nutrients consist of inactivated yeast and autolysates. They contain no inorganic N and only 3 mg/L N for every 100 mg/L added).
- Six-twelve hours after inoculation (2-3 Brix drop)
- End of growth/exponential phase (1/3 sugar depletion)
Note that at ½ sugar depletion the yeast cannot utilize N since alcohol accumulation prevents uptake. This residual N can then be utilized by other organisms such as Brettanomyces spp.
Results of Deficient YAN
From a practical point of view, the problem of juice nitrogen composition is primarily linked to juices with suboptimal concentrations of nitrogen (<150 mg/L), and higher risk of slow or stuck fermentation. Low YAN (< 200 mg/L) is associated with production of sulfur compounds, e.g. hydrogen sulfide, which results from the nitrogen demand for yeast growth. The amount of H2S produced is dependent on the yeast strain, the sulfur precursor compound, the culture growth rate, and the enzymatic activity immediately before nitrogen depletion.
When working with very low YAN juices, researchers have observed that other nutrients can also be low. Therefore, when YAN is low and other nutrient deficiencies are suspected, it may be useful to add a proprietary yeast food that contains more complex forms of N, as well as vitamins, lipids and minerals. Continued H2S production after N addition suggests a general vitamin deficiency, though other causes are also possible. Most yeast suppliers can advise on the use of yeast foods, which are generally produced from inactivated yeast, e.g. GoFerm® or similar additives.
In summary, low must YAN leads to low yeast populations and poor fermentation vigor, increased risk of sluggish/stuck/slow fermentations, increased production of undesirable thiols (e.g. hydrogen sulfide) and low production of favorable sensory compounds including esters and long chain volatile fatty acids.
Results of Excessive YAN
High must YAN leads to increased biomass and higher maximum heat output due to greater fermentation vigor. Overuse of DAP can also stimulate overproduction of acetate esters, especially ethyl acetate, resulting in the perception of volatile acidity (VA) and suppression of varietal character. High YAN (exceeding 450-500mg/L YAN) can stimulate ethyl acetate production by many yeast strains. Increased concentrations of haze-causing proteins, urea and ethyl carbamate and biogenic amines are also associated with high YAN musts. The risk of microbial instability, potential taint from Botrytis-infected fruit and possibly atypical aging character is also increased.
Main Flavor Changes Affected by Nitrogen
In general, YAN can affect TA and the balance of organic acids which can affect flavor. Malic acid consumption increases with increasing DAP concentration, irrespective of yeast strain. When total nitrogen is increased by adding ammonium to a medium containing very low levels of YAN, the production of higher alcohols is initially increased, but then tends to decrease after a peak between 200-300mg/L YAN. This activity depends on various factors, including yeast strain and fermentation conditions. Higher alcohols are characterized by fusel-like odors, and are generally thought to contribute to the complexity of wine fermentation bouquet. However, when present in very high concentrations they can have a negative impact on wine aroma, mainly because they mask fruity characters.
Of course, intermediate must YAN favors the best balance between desirable and undesirable chemical and sensory wine attributes. The key is to have timely and accurate YAN must concentration data immediately before primary inoculation. Recognizing that measurement is difficult in a winery setting, we encourage use of commercial and extension labs that offer YAN measurements, so that the winemaker might make an informed decision regarding supplemental nitrogen additions.
AWRI: Maurizio Ugliano, P. A. H., Markus J. Herderich, Isak S. Pretorius. 2007. Nitrogen management is critical for wine flavour and style. AWRI Report: The Australian Wine Research Institute, vol. 22. Wine Industry Journal, Glen Osmond (Adelaide), South Australia 5064, Australia.
Barthe, C., M. Dorais, G. Dubé, P. Angers, and K. Pedneault. 2013. Abstracts from Presentations at the ASEV–Eastern Section, 2013, Winston-Salem, NC. 64:417A.
Bell, S.-J., and P. A. Henschke. 2005. Implications of nitrogen nutrition for grapes, fermentation and wine. Australian Journal of Grape and Wine Research 11:242-295.
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by Molly Kelly, Enology Extension Educator
In blog post #1 (June 29th) Penn State Extension covered current COVID-19 state guidelines for the reopening of Pennsylvania tasting rooms. In the second post (July 13th) we covered federal guidelines of general best practices related to the reopening of tasting rooms and COVID-19 drawn from guidance by the Centers for Disease Control (CDC), US Department of Labor, American Industrial Hygiene Association (AIHA), Occupational Safety and Health Administration (OSHA) and the Food and Drug Administration (FDA).
These agencies offer considerations for ways in which operators can protect employees, customers, and communities and slow the spread of COVID-19. These considerations are meant to supplement—not replace—any state, local, territorial, or tribal health and safety laws, rules, and regulations with which businesses must comply.
In this third and final post we will discuss additional federal guidelines to more safely open tasting rooms.
- Make sure ventilation systems are operating properly and increase circulation of outdoor air as much as possible (ex: open windows/doors, prioritize outdoor seating).
- Do not open windows/doors if doing so poses a safety or health risk (ex: fall risk, triggering asthma attacks).
- Maintain indoor relative humidity at 40-60%.
- Consider using portable HEPA filtration units.
- If fans such as pedestal fans or hard mounted fans are used in the bar, take steps to minimize air from fans blowing from one person directly at another individual.
NOTE: Contact an occupational health and safety professional or ventilation specialist for advice on how to best utilize ventilation systems.
Signs and Messages
- Post signs in highly visible locations (ex: restrooms, entrances) that promote everyday protective measures (ex: proper handwashing, wearing masks).
- Place signs at the entrance that encourages customers to follow physical distancing requirements. Find creative and fun ways for staff and security to encourage customers to follow these guidelines.
- Place signs asking customer and employees to wash hands before and after using the restroom.
- Refer to CDC’s free print and digital resources.
Promoting Behaviors that Reduce Spread/Protect Employee Health
- Stay home when appropriate.
- Develop policies that encourage sick employees to stay home.
- Employees should stay home if they have tested positive for or are showing COVID-19 symptoms.
- Employees who have recently had a close contact with a person with COVID-19 should stay home and monitor health.
- Stagger or rotate shifts to limit number of employees present at same time.
- Minimize the number of customers present at one time (refer to previous post for PA-specific guidelines).
- Designate a COVID-19 Point of Contact for each shift to be responsible for responding to COVID concerns.
Establish protocols for execution upon discovery that the business has been exposed to a person who is a probable or confirmed case of COVID-19 including:
- Close off areas visited by the person who is a probable or confirmed case. Open outside doors and windows and wait a minimum of 24 hours, or as long as practical, before beginning cleaning and disinfection. Ensure safe and correct use and storage of EPA-approved List N disinfectants.
- Prepare to isolate and safely transport those who are sick to their home or a healthcare facility.
- Identify employees that were in close contact (within about 6 feet for about 10 minutes) with a person with a probable or confirmed case of COVID-19 from the period 48 hrs before symptom onset to the time at which the patient isolated. Advise them to stay home and self-monitor for symptoms and follow CDC guidance if symptoms develop.
- Consistent with applicable law and privacy policies, have staff self-report to the designated Point of Contact if they have symptoms of COVID-19 or were exposed to someone with the virus within the last 14 days.
- Close off areas used by a sick person. Wait at least 24 hours before cleaning and disinfecting.
- Notify local health officials of any case of COVID-19 while maintaining confidentiality in accordance with the Americans with Disabilities Act (ADA).
- Communicate to the customers what the bar is doing to mitigate the spread of COVID-19 (e.g., disinfection routine, health policies for staff, and health & safety measures in place).
- Consider placing signage on tables to show that they have been disinfected after previous customers.
- Communicate that the bar has the right to refuse service to anyone exhibiting symptoms or not following guidelines (ex: physical distancing).
- Platforms for communication could include websites, reservation processes, hand-outs, and outdoor signage.
Disclaimer: Penn State Extension educational programs, content, and recommendations (including text, graphics, and images) are for educational purposes only. The Pennsylvania State University does not guarantee the accuracy, adequacy or completeness of any information and is not responsible for any errors or omissions or for the results obtained from the use of such information.
- FDA. Best Practices for Retail Food Stores, Restaurants, and Food Pick-Up/Delivery Services During the COVID-19 Pandemic.
- OSHA. Retail Workers and Employers in Critical and High Customer-Volume Environments.
- CDC. Implementation of Mitigation Strategies for Communities with Local COVID-19 Transmission
- CDC. What to Do if You are Sick
- CDC. June 30, 2020 Considerations for Restaurants and Bars
- Numerous wellness questionnaire examples are available online (e.g., South Dakota Department of Health’s COVID-19: Employee Screening Questions and Guidelines).BusinessScreening_Q&A.pdf
- July 2, 2020 Governor’s Process to Reopen Pennsylvania
- COVID Prevention Plan for Food Establishments. June 2, 2020
- COVID-19 Risk Assessment Form for OSHA Guidelines May, 2020
- Nyco: What’s the Difference between Sanitizers and Disinfectants? Accessed July 6, 2020
- AIHA. version 2, June 19,2020 Reopening-Guidance-for-the-Bar-Industry_GuidanceDocument.pdf