Articles & blog posts
Unless otherwise cited, this section contains original content on topics relevant to the Virginia wine industry. Information provided is based upon the research findings, experience, and best judgement of Virginia Tech personnel at time issued. Virginia Tech Enology Extension does not endorse or represent any particular product, treatment, service or individual.
Viticulture & Enology 2020 Season Recap
Tremain Hatch (VT Viticulture Research/Extension Associate) and I released a joint V&E recap of the 2020 harvest season. Click link below to view PDF. It's lengthy, so in case you don't read 'til the bitter end, in conclusion:
"Throughout harvest, “The Gambler” by Kenny Rogers plays in repeat in our heads. We hope that you knew when to hold ‘em and when to fold ‘em this season, and that these “state of the grape in the state” reports helped along the way. We welcome feedback on how to make the Sentinel Vineyards project more useful and robust in future years, and once again thank the Virginia Wine Board for their funding, the Virginia Tech Analytical Services Lab for processing the fruit chemistry samples, and most of all, our industry partners for their enthusiasm, dedication and effort during the busiest time of the year. "
12/04/20
2020 Sentinel Vineyards Report 7
Hours of daylight are lessening, and likewise this report (and subsequent ones, I suspect) will be somewhat abbreviated, as it seems ripening of Cabernet Franc in much of the state is slowing down. While there was an average 5% increase in TSS last week (report 6), this week’s average increase was only 1%. Correspondingly, sugar loading values remained static or increased by 0.01 g TSS/berry. Likewise, pH experienced minimal changes, remaining in the 3.6s. TAs averaged 4.41 g/L across the state, which is a 0.01 decrease from last week.
One juice chemistry metric that hasn’t been reported in much detail throughout this Sentinel Vineyards series is YAN (yeast assimilable nitrogen). As previously mentioned, this is because it is highly variable depending on site, cultivar, and viticultural practices, so it is not feasible to make generalizations that would be helpful for assessing regional harvest conditions. However, it can be noted that (as expected), a gradual, slight increase in YAN has occurred across berry maturation.
Figure 1: YAN by site by sample week
This is shown in Figure 1, as a function of sample week, and in Figure 2, as a function of TSS. The majority of samplings have ranged from ~50 – 125 mg/L N; the average YAN across all sites across the season is 172 mg/L N. This observation is hopefully interesting in and of itself, and also serves as a long-winded way to insert a friendly reminder that it can be helpful to check YANs prior to fermentation to determine whether yeast nutrient additions are advisable :-)
Figure 2: YAN by site by TSS
And that’s all for this week! Good luck as harvest continues. To view prior Sentinel Vineyards reports, or to subscribe to receive them, please visit vtenology.com. And of course, please let us know if there's anything else we can do to support your grape growing and winemaking endeavors.
(10/07/20)
2020 Sentinel Vineyards Report 6
Hi folks! It’s that time of the year… temperatures and leaves are starting to drop, it’s pumpkin spice everything, and this message probably finds you knee deep (figuratively, and possibly literally) in sticky grape pomace!
Taking a look at the Cabernet Franc still on the vine: TSS continues to increase throughout most of the state (Fig. 1)., averaging between 20 – 23 °Brix. Crunching the numbers, we saw a fairly consistent 5% increase as compared to last week. The decrease (color coded by region) of TA throughout the sampling season in shown in Figure 2. There was approximately a 5 – 10% decrease since last week, and the average value across Virginia is 4.52 g/L.
Figure 1: TSS by region across sample weeks
Figure 2: TA by region by sample week
Figures 3 – 5 feature a close up of ripening in the past 7 – 10 days by site. Across the commonwealth, pHs are in a pretty tight cluster (within 0.1 pH units); most samplings have been between pH 3.63 – 3.71. As seen in Fig. 3, there is an outlier to this trend: one of our Shenandoah Valley sites has a pH in the mid 3.5s. This lower value is somewhat remarkable, as it is simultaneously on the riper side of current berry maturation averages (21.3 °Brix; 0.32 g TSS/berry).
Examining pH as a function of sugar loading gives perspective by spreading out these observations (perhaps, some would argue, to the point of negligible differences!). In Figure 4, it is seen that, on average, Northern VA has the highest sugar load (0.31 g TSS/berry), followed by a tie between Central and Southern VA at 0.28 g TSS/berry. Shenandoah’s numbers are arguably too disparate to average (but if curious, it is 0.26 g TSS/berry), and the Hampton Roads' fruit is at 0.23 g TSS/berry.
Figure 3: pH by TSS by site
Figure 4: pH by sugar loading by site
Finally, turning to Figure 5, malic acid is plotted against TA values. Overall, malic acid concentrations are quite low at this point, ranging from ~1 – 2.5 g/L. Delving into regional comparisons, Southern and Central VA trends the lowest, Hampton Roads trends the highest, Shenandoah is in the middle, and Northern VA is a mix. As discussed in Report 3 (see below), malic acid and TA concentrations are correlated, but imperfectly. A good example of this is seen in the Northern VA #1 and Shenandoah #2 data points. These samples contain nearly identical malic acid levels, yet have a 0.5 g/L difference in TA. From a chemical perspective, this indicates that the higher TA sample (i.e. Northern VA #1) has a greater number of protons, most likely due to a higher concentration of tartaric acid. From a winemaking perspective, this can be helpful for understanding how certain treatments, e.g. malolactic fermentation and cold stabilization, could affect the final wine TA and pH. Speaking of which, for anyone who is wondering, the Northern VA sample is 0.06 pH units higher than the Shenandoah sample.
Figure 5: Malic acid by TA by site
And that’s all for this week! Good luck as harvest continues. To view prior Sentinel Vineyards reports, or to subscribe to receive them, please visit vtenology.com. And of course, please let us know if there's anything else we can do to support your grape growing and winemaking endeavors.
(09/30/20)
2020 Sentinel Vineyards Report 5
In the 90’s country music hit “Time Marches On” (by Tracy Lawrence), there is the quintessential line “The only thing that stays the same is everything changes. Everything changes.” And so it does, hopefully for the better in regards to your fruit chemistry! At this point in the season, we are down to a lone Chardonnay sampling from Northern Virginia. There, TSS is up another 1.5 °Brix to 20.7 °Brix and sugar load is at 0.31 g TSS/berry. This is nicely balanced by a TA of 5.5 g/L and ~2 g/L malic acid.
Likewise, Cabernet Franc is marching on: the average TSS in Central, Northern, and Southern Virginia is 20.4 °Brix, and Hampton Roads has increased over 1 °Brix to 14.7 °Brix. As can be seen in Figure 1, this corresponds to sugar loading values near (or exceeding) 0.3 g TSS/berry. It is useful to see that loading may be slowing down in parts of Central and Southern VA (apologies for the squiggly lines), while continuing to increase in other regions.
Figure 1: Sugar loading by region across sample weeks
Conversely, malic acid has declined to ~1-2 g/L in much of the commonwealth (Figure 2), and pHs are in the mid-to-upper 3’s. Across samplings, TA values fell by 1 g/L in the last week (Figure 3). Southern VA’s values continue to be on the low end of the spectrum (~3.7 g/L), and Hampton Roads’ are the highest (~4.8 g/L). TA concentrations in both Central and Northern VA’s averages have fallen by about 50% in the past month, and their means are now 4.3 and 5.2 g/L respectively.
Figure 2: Average malic acid by region by sample week
Figure 3: TA by region across sample weeks
Good luck as harvest continues. To view prior Sentinel Vineyards reports, or to subscribe to receive them, please visit vtenology.com. And of course, please let us know if there's anything else we can do to support your grape growing and winemaking endeavors.
(09/23/20)
2020 Sentinel Vineyards Report 4
Hope that harvest continues to go well for everyone. Our Chardonnay reporting is dwindling, as several of our industry partners have brought in the fruit. From those remaining, Total Soluble Solids (TSS) averaged ~19 °Brix and sugar loading was ~0.33 g TSS/berry across the Shenandoah Valley, Central, and Northern VA regions. A quick comparison to historical data indicates a lower than average ripeness at harvest, but we’ll wait until all the fruit is brought in (and more data examined) before saying that with any certainty. Berry acid metrics showed slightly more variation by region. Shenandoah Valley’s measurements were the highest, with malic acid at ~5 g/L and TA at ~8.4 g/L. Central VA was in the middle, with malic averaging 4.1 g/L and TA at ~6.5 g/L. And Northern VA was the lowest, with malic and TA at 2.6 g/L and 6.2 g/L respectively.
Looking to Cabernet Franc, it’s exciting to watch the evolution across all 5 regions. TSS are plotted in Figures 1 and 2. In Figure 1, the average TSS by region by sampling week is shown, and in Figure 2, the TSS for each site is plotted, and then grouped by region. Either way, the seasonal status is as follows: TSS currently averages ~19.5 °Brix across much of the state, gaining about 1 °Brix in the last week. Shenandoah Valley is slightly behind at ~17.8 °Brix and Hampton Roads is showing development at ~13.5 °Brix.
Figure 1: Average TSS by region by sample week
Figure 2: TSS by site across harvest (to date)
As with Chardonnay, there is more spread in TA values in Cab Franc depending on both region and ripeness level. Values to date are plotted by TSS by site in Figure 3. At present, Southern VA’s TA is the lowest (~4.5 g/L), followed by incremental increases in Central VA (5+ g/L), Northern VA (6+ g/L), Hampton Roads (7+ g/L), and finally Shenandoah (8+ g/L). These values correspond to decreasing pHs and increasing malic concentrations. For more information on pH and TA, and ways to tweak these metrics in your grape/wine matrix, please see the briefing below, which was a collaborative effort between the Winemakers Research Exchange and Virginia Tech Enology Extension. It is posted to both of our platforms, and includes protocols for measuring pH*, measuring TA, and conducting acid trials.
Figure 3: TA by TSS by site across harvest (to date)
As always, be sure to subscribe to the enology extension mailing list to receive these reports, and other timely updates. If interested in bolstering the metadata for our Sentinel Vineyards analysis (or simply to have a central location to log data), please enter “Events”, e.g. fruit chemistry, spray applied, hail damage, on GrapeIPM.org. And of course, please let us know if there's anything else we can do to support your grape growing and winemaking endeavors.
(09/16/20)
pH, TA, and acid adjustments
a collaboration between VT Enology Extension and the Winemakers Research Exchange
Acids in Wine
by Dr. Beth Chang, Enology Extension Specialist, Virginia Cooperative Extension
pH is a major contributor to the following factors in wine: 1) microbial stability, and 2) color stability. Lower pH, preferably < 3.6, is important for decreasing risk of spoilage organisms and increasing efficacy of SO2. Likewise, a lower pH increases color stability, and keeps color molecules, i.e. anthocyanins, in the preferred color range of red-purple, rather than purple-brown. In addition, lower pH can increase rates of reactions for various wine components during storage (1,2).
When we measure pH, we are measuring the strength of the acid (or acids) in a solution, in this case: grape juice or wine. Because of the word “acid”, it is easy to assume that pH is useful in evaluating the acidity, or perception of sourness. And yes, pH does have a loose inverse correlation to sourness. However, a much more predictive metric is TA (titratable acidity), which relates to the concentration of acids in juice and wine. TA has a much stronger (nearly linear) and direct correlation to sourness: rising TA concentrations will result in increasingly sour taste (2,3).
Typically, there is an inverse relationship between pH and TA: lower pHs indicate higher TAs and vice versa. However, the two do not ever track in a perfectly predictable way, and there are times when both high pH and high TA can be present simultaneously in a juice or wine. The two major reasons for this are: 1) different organic acids (which are all weak acids) have different buffering capacities, or to put it another way, some organic acids, e.g. tartaric acid, are stronger weak acids than others. This means that their addition or removal will have a larger impact on pH. Therefore, the relative amounts of organic acids will lead to different pHs at the same TA. And 2) higher concentrations of metals (e.g. K+, Ca+2, Mg+2) in the grape juice and wine matrix can result in increased pHs at a given TA because the metals likewise increase buffering capacity, while masking the total number of acid molecules (i.e. total acidity) through hydrogen displacement (2). This second cause is particularly pertinent in the mid-Atlantic region (e.g. Virginia), where excessive potassium absorption frequently occurs (4).
When looking at the pH and TA of a must or wine, it’s helpful to have some reference points against which to compare values. Generally accepted industry ranges for must pH would be 3.0 – 3.4 for whites, and 3.2 – 3.4 for reds (1). The resulting final wine product is broadly between pH 3 – 4, with whites on the lower side and reds on the higher side, e.g. 3.3 – 3.7 (2). Typical values for TA (measured as g tartaric / L) are between 5 – 8 g/L. Red wines tend to skew lower than whites because the potassium extracted from the grape skins will cause increased potassium bitartrate precipitation (1).
Measuring pH and TA is essential prior to fermentation, and can also be useful well before harvest to get a better picture of overall fruit quality. As grape berries mature, pH will increase and TA will decrease. Factors related to accelerated berry maturation, e.g. warm temperatures, will result in a faster rise in pH and rate of decline in TA (5).
If you are interested in learning more about “typical” pH, TA, and other fruit ripening metrics in Virginia, be sure to subscribe to VT Enology Extension’s mailing list so that you can receive Sentinel Vineyards reports. The Sentinel Vineyards initiative is a Virginia Wine Board sponsored collaboration between Virginia Tech’s Viticulture and Enology Extension team, the WRE, and a network of industry partners, to collect, analyze and disseminate data on the status of the grape growing and winemaking season. We hope that the information provided on relevant statewide viticultural, pathological, meteorological, and enological parameters will aid in your decision-making process. In addition, these evaluated metrics, e.g. disease incidents, weather conditions, fruit chemistry, provide longitudinal data for establishing a baseline tailored to Virginia’s climate.
How to measure acidity in fruit and juice samples
by: Dr. Beth Chang and Dr. Joy Ting
In order to make good decisions about additions to juice and wine, you need to have a good measure of what you are starting with. Much of the information you need can be obtained in the winery lab with minimal equipment, time, and expense.
pH: The most important measurement is the pH of the wine. To ensure you have an accurate measure of pH, you must have a good working pH meter that is properly calibrated. Once you get your pH meter up and running, you will also use it for acid trials and measurement. Though each pH meter is different, there are a few principles to keep in mind when calibrating and measuring pH of grape juice and wine. Click here for a protocol and best practices.
*As mentioned in protocol, for a good video on proper usage of a pH electrode, click here. For an excellent video on how a pH electrode works, click here.
Acid trials: There is a complex relationship between the concentration of acids in grape juice and wine and their effect on the pH of the solution. Grape juice and wine are buffered solutions, meaning there are a number of components in the juice that will resist changes in pH when acid is added (known as the buffering capacity)(6). The best way to determine how a juice or wine will respond to addition of acid is to measure it yourself on the lab bench. This process is very simple as long as you have a well calibrated pH meter (link again), and a micropipette. Click here for a protocol.
Titratable acidity: Technically, titratable acidity is the sum of all of the free (dissociated) and bound (undissociated) protons in a solution. This measurement correlates to the total amount of acid molecules in wine including all of the tartaric, malic, citric, lactic, acetic and succinic acids as well as which form they are in (6,7). The TA of a juice or wine can give you a good indication of the sensory perception of acidity. Though there is a little bit of initial set-up, TA can also be measured easily in the winery lab with a well calibrated pH meter, a burette and a stir plate. Click here for a protocol.
Sending out samples: If you want to verify your in-house readings, or if you want additional tests such as malic acid and YAN, you may consider sending samples for analysis at a service lab. Be sure to follow any instructions given by that lab in terms of sample size, hours/days of delivery, and sample preparation. Without intervention (use of preservative, freezing or boiling), grape juice samples will likely begin fermentation during shipping, altering several chemical parameters. Due to potential of tartrate precipitation, juice and wine samples that have been frozen may have some alteration of pH and TA (malic acid and YAN will remain the same with freezing). To determine the best method of shipping for your samples and desired analysis, it is recommended to contact the lab and ask before sending samples. Lab personnel are generally very friendly and informative and can be a huge help when determining the best course of action.
Strategies for Acid Adjustment
by Dr. Joy Ting, Research Enologist and Extension Coordinator, Winemakers Research Exchange
Acid adjustment is a common occurrence in Virginia winemaking, and may be needed in some cases in 2020. If you find yourself in the situation where you need to add acid, here are a few things to keep in mind:
Gather as much information as you can by measuring pH, TA, and doing an acid trial. It is best to do acid trials and run TA on samples just before inoculation, to account for any differences that have occurred during settling or cold soak. For white, this means after racking. At the juice stage, it is difficult to assess the sensory effects of acid additions, but if you are thinking of adding acid to finished wine, a taste trial is also a helpful tool. See the above for protocols for each of these tests.
There are no hard and fast rules for pH and TA limits (7), but rather principles and ranges to keep in mind. It is possible you will need to compromise on one target or another. Keep the principles of wine acidity in mind as you make your choices. For example, though titratable acidity values generally range from 5-8 g/L, these values are usually higher for sparkling wine (up to 10 g/L)(8).
Fermentation changes things. It is likely the pH will increase and TA will decrease during fermentation due to the effects of increasing ethanol, precipitation of bitartrate, utilization of malic acid by yeast, production of succinic acid, consumption of amino acids, and extent of malolactic fermentation (6).
Acid additions:
Timing: It is generally preferred to add acid earlier vs. later in order to maximize the benefits of microbial stability and to allow for better flavor integration. However, it is more difficult to know exactly what you will need pre-fermentation. Some winemakers prefer to add ¾ of the anticipated addition prior to fermentation and the remainder after fermentation, when sensory trials can be conducted and the effects of fermentation are fully known (6).
Which acid to add: Tartaric acid is the most common acid used to adjust the pH of the wine. Unlike malic and citric acids, tartaric acid is relatively insensitive to microbial decomposition (6). Addition of tartaric acid will result in a greater change in pH than the same concentration of malic acid because tartaric is more highly ionized than malic at normal wine pH and is a “stronger” weak acid, meaning it can contribute protons more easily to lower the pH (7,8). One disadvantage of adding acid as tartaric is loss due to crystallization as potassium bitartrate. This is especially pronounced in juice and with high levels of potassium (7).
Some winemakers feel that large additions of tartaric acid shift the normal sensory profile of the wine and therefore prefer to add a blend of tartaric and malic acids (8). Wine acids have been described for their sensory character beyond mere acidity (9).
The true proportion of tartaric to malic acid in wine varies by cultivar and region (6,10,11). The Sentinel Vineyard Project and WRE are tracking these metrics in several varieties in Virginia in 2020. One important note: do NOT add citric acid before fermentation. Citric acid can inhibit fermentative enzymes and can be metabolized by lactic acid bacteria to form acetic acid (8).
From The Taste of Wine, Emile Peynaud (1987)
Decreasing acidity
Malolactic Fermentation: It is generally thought that malic acid has a stronger perception of acidity than lactic acid, so one strategy to decrease sourness is to let the wine undergo malolactic conversion (or inoculate it with ML bacteria). This will also increase the pH of the wine, the extent of which depends on the buffer capacity of the specific wine, averaging 0.1 – 0.2 pH units per gram of malic acid converted (6). If you choose to inoculate with malic acid bacteria, keep in mind that these microbes also consume citric acid to produce diactyl. Choose a strain that fits the sensory impact you are looking for (high vs. low diacetyl). Also, keep in mind that lactic acid levels of 1.5 g/L will slow down malic acid bacteria and levels above 3 g/L may inhibit these bacteria (12).
Cold Stabilization: During cold stabilization, potassium bitartrate precipitates from the wine solution resulting in as much as 2 g/L decrease in TA (8). The effect on pH depends on the initial pH of the wine. When tartrate is lost, the equilibrium of these three forms will shift. If the initial pH of the wine is greater than 3.65, the equilibrium will shift in a way that takes up a proton, which increases the pH. If the initial pH of the wine is less than 3.65, the shift in equilibrium will result in release of a proton, and decrease in pH (6–8). (Boulton points out that in an ethanol based solution, this break point may be closer to 4.1, good news for winemakers (6)).
The special case of high pH, high TA
The special case of high pH, high TA leads to some difficult decisions for winemakers. This situation is caused when high levels of potassium are traded off for protons by grapes (increasing the pH), leaving tartrate ions behind (still contributing to TA). It is common in cold climates when malic acid is elevated due to cool nights but potassium is present (7) and has also been reported in Australia due to high potassium levels (10). When this is the case, knowing TA levels, malic acid levels, and doing acid trials becomes even more important. The AWRI recommends large acid additions as early as possible in fermentation in an attempt to precipitate out excess potassium. Ion exchange can also be used for this purpose (10).
References
(1) Boulton, R. B.; Singleton, V. L.; Bisson, L. F.; Kunkee, R. E. Principles and Practices of Winemaking; Springer US: Boston, MA, 1999.
(2) Waterhouse, A. L.; Sacks, G. L.; Jeffery, D. W. Understanding Wine Chemistry; John Wiley & Sons, Ltd: Chichester, UK, 2016.
(3) Plane, R. A.; Mattick, L. R.; Weirs, L. D. AN ACIDITY INDEX FOR THE TASTE OF WINES. American Journal of Enology and Viticulture 1980, 31 (3), 4.
(4) Wolf, T. K. Wine Grape Production Guide for Eastern North America; Plant and Life Sciences Publishing: Ithaca, New York, 2008.
(5) Dokoozlian, N. K.; Kliewer, W. M. Influence of Light on Grape Berry Growth and Composition Varies during Fruit Development. 6.
(6) Boulton, R.; Singleton, V. L.; Bisson, L. F.; Kunkee, R. E. Principles and Practices in Winemaking; Chapman and Hall, Inc: New York, 1996.
(7) Jackson, R. S. Wine Science: Principles and Applications, 4 edition.; Academic Press: Amsterdam, 2014.
(8) Zoecklein, B.; Fugelsang, K. C.; Gump, B. H.; Nury, F. S. Wine Analysis and Production; Springer: New York, 1995.
(9) Peynaud, E. The Taste of Wine: The Art and Science of Wine Appreciation; The Wine Appreciation Guild LTD: San Francisco, California, 1987.
(10) Ask the AWRI: Winemaking with High PH, High TA and High Potassium Fruit. Grapegrower and Winemaker2018, October (657).
(11) Kliewer, W. M.; Howarth, L.; Omori, M. Concentrations of Tartaric Acid and Malic Acids and Their Salts in Vitis Vinifera Grapes. American Journal of Enology and Viticulture 1967, 18, 42–54.
(12) Scottlabs. Fermentation Handbook; 2018.
(09/11/20)
2020 Sentinel Vineyards Report 3
Hope you all had a happy, sunshine-filled Labor Day weekend, whether you were monitoring grapes in the vineyard, checking tanks in the cellar, or sipping the fruits of your labor from last year. Speaking of the fruits of your labor, let’s take a look at the chemistry numbers from last week, focusing on Chardonnay first. In the Central region, ripening parameters seem to be slowing down in some locations. This can be seen in Figure 1, which compares berry weight accrual to sugar loading. The curve flattened for Central VA sites 2 and 3, which was in contrast to Central VA site 1 (going strong!) and both Northern VA sites (picking up steam!). This is corroborated by examining the percent change in sugar loading: the average increase for the Central sites was 20% two weeks ago, and 9% last week. In contrast, the sugar loading rate has increased in Northern VA from 13 to 33%. Evaluating acid metrics (Figure 2), decreasing TA and increasing pH seem to be tracking in a loosely uniform manner in both Northern and Central VA, with a 0.1 unit decrease in pH for every 1-2 g/L drop in TA.
An interesting side note: there was a fairly dramatic drop in malic acid between collection weeks 2 to 3, as opposed to weeks 1 to 2, or weeks 3 to 4 (Figure 3). Specifically, between weeks 2 to 3, the malic acid in grape samples from Central VA decreased by ~33% and those from Northern VA decreased by 40%. In comparison, malic acid decreased by 18% and 14% in Central and Northern VA respectively from week 3 to week 4 (i.e. the most current time point). To delve a little deeper, these changes are plotted in Figure 4a (note: changes are by site, rather than by region), and compared to changes in pH (Figure 4b). The comparison of change in malic acid by week again shows the significant decrease in week 3 (i.e. from week 2 to week 3), and corresponds to the largest percent increase in grape berry pH (max. = +6%).
What does this suggest, beyond that I must have an incredibly boring life to be so interested in such observations? Well, as many of you know, it points to differing concentrations of the respective organic acids in the grape berry, and to the differing buffering capacities of these organic acids, which is exacerbated by metal content (e.g. K+, Ca+2, Mg+2). The phenomena is nothing new, yet the mechanism by which malic acid is utilized in the grape berry is still not fully understood, nor do we have predictive models for pH and TA (i.e. big influences on final wine stability) that factor in these variables. For now, the WRE and VT Enology will be putting out a flash bulletin on what we do know about acid chemistry and its effects on winemaking, but this is a trend that we, meaning the VT Viticulture and Enology Extension Team, the WRE, and perhaps some of you, will continue to investigate throughout the season and beyond.
Turning to a short update as we continue to accumulate data on Cabernet Franc: a nice increase in TSS was seen over the past week in several regions of the commonwealth. Northern VA averaged 18.8 °Brix, while Central VA trailed by a hair at 18.3 °Brix, and Chesapeake Bay was at 17.3 °Brix (an increase of 2.5 °Brix). Hampton Roads is progressing more slowly (12.7 °Brix), and Southern VA gained slightly (19.3 °Brix). Sugar loadings ranged from 0.19 – 0.26 g TSS per berry across the state. As shown in Figure 5, TAs continue to drop, and are getting into a typical winemaking range. pHs continue to rise; we’ll keep our fingers crossed that TSS keeps pace.
As usual, be sure to subscribe to the enology extension mailing list to receive these reports, and other timely updates (and tell your friends!). If interested in bolstering the metadata for our Sentinel Vineyards analysis (or simply to have a central location to log data), please enter “Events”, e.g. fruit chemistry, spray applied, hail damage, on GrapeIPM.org. And of course, please let us know if there's anything else we can do to support your grape growing and winemaking endeavors.
(09/08/20)
2020 Sentinel Vineyards Report 2
I know it’s been a hectic week for many of you, as recent rainfall pushed harvest decisions for some varieties/wine styles around the state. We'll be hoping for some drier weather, and those slightly cooler temperatures that are in the forecast. As harvest planning continues, let’s take a look at week 2 of the Chardonnay data: Chardonnay TSS ranged from ~15-17 °Brix across the Central, Northern, and Chesapeake Bay regions. For those interested in sugar loading (sugar per berry), this meant an average of 0.25 g sugar (or TSS) per berry, based on a 200 berry sample size. TAs have been declining by approximately 2 g/L per week; the current average is 8.7 g/L with no noticeable difference between regions. This corresponds to relatively high pHs, given berry maturity. For example, a pH of 3.76 was recorded for a sample at 15.3 °Brix last week; that same location had a pH of 3.57 at 22.4 °Brix last year. We are still accumulating observations from around the state; here are preliminary figures from Central VA:
Marginal decreases from week 1 to week 2 were observed in malic acid, followed by a more rapid decline of ~2 g/L from weeks 2 to 3. Malic will continue to be analyzed across the state across the season, as knowing its concentrations may prove helpful when weighing options for mitigating higher pHs coupled with lower TSS. On that note, the Winemakers Research Exchange (check out their newest newsletter) and VT Enology Extension will be compiling a bulletin on the topic next week.
And now, let’s talk about the first samplings of Cabernet Franc! There was considerable variation in fruit chemistry: the highest TSS were, as expected, recorded in Southern VA (~18 °Brix), while Hampton Roads was the lowest (~12 °Brix). Samples from much of the rest of Virginia (i.e. Shenandoah Valley, Chesapeake Bay, Central and Northern VA) were in the 15-17 °Brix range. Statewide, the average sugar loading value is 0.19 g TSS/berry, indicating grape maturation is progressing, though hopefully we will get some warm, sunny hang time before harvest. Similar to last week’s 1st Chardonnay report, I am cautious to even hint at “trends” based on the data. Nevertheless, pHs again seemed elevated considering ripeness levels. Shenandoah Valley retained the most acid, at pH of 3.1 and TA of 11.72 g/L. Samples from Northern VA and Chesapeake Bay were in the pH 3.2-3.3 range, with TAs in a tight cluster of ~10 g/L. Looking to the remaining regions, pHs escalated from the mid 3.4s in Central VA, to the mid 3.5s in Hampton Road, and approached 3.7 in Southern VA. YAN levels varied by an order of magnitude and appear to be site specific; we will continue to monitor and report any distinguishable features as the season progresses. Likewise, phenolics analysis is underway and will be communicated in the coming weeks.
Please be sure to subscribe to the enology extension mailing list to receive these reports, and other timely updates. If interested in bolstering the metadata for our Sentinel Vineyards analysis (or simply to have a central location to log data), please enter “Events”, e.g. fruit chemistry, spray applied, hail damage, on GrapeIPM.org. And of course, please let us know if there's anything else we can do to support your grape growing and winemaking endeavors.
(08/31/20)
2020 Sentinel Vineyards Report 1
At this point, I hope that many of you are aware of the Sentinel Vineyards initiative, but as we kick off the fruit analysis portion of the project, here is a quick recap: The Sentinel Vineyards project is a collaboration between Virginia Tech’s Viticulture and Enology Extension team (Tony Wolf, Mizuho Nita, Tremain Hatch and Beth Chang) and a network of industry partners to collect, analyze and disseminate data on the status of the grape growing and winemaking season. We hope that the information provided on relevant statewide viticultural, pathological, meteorological, and enological parameters will aid in your decision-making process. In addition, these evaluated metrics, e.g. disease incidents, weather conditions, fruit chemistry, provide longitudinal data for establishing a baseline tailored to Virginia’s climate. We thank the Virginia Wine Board for funding this project, and our industry partners for contributing so much time and energy to making it a success. For those interested in aiding Sentinel Vineyards (or simply to have a central location to log data), please enter “Events”, e.g. fruit chemistry, spray applied, hail damage, on GrapeIPM.org. The additional data points are helpful for identifying trends within and across regions.
With the 2020 growing season well underway, I presume many of you have been reading Dr. Nita’s Grape Pathology blog and Dr. Wolf’s Viticulture Notes. Now that the veraison-to-harvest sprint has begun, be sure to subscribe to the enology extension mailing list to receive timely updates on fruit ripening parameters. Speaking of which, samples are beginning to roll in from around the state. For this pilot year, Chardonnay and Cabernet Franc were agreed upon as the “sentinel varieties” due to being widely planted, the early ripening of Chardonnay and the tendency to let Cabernet Franc hang as late as possible. So far, Chardonnay samples from Central VA, Northern VA, and Shenandoah contain total soluble solids (TSS) averaging between low 13 to high 14 °Brix. A 1 °Brix increase from week 1 to week 2 was observed, as expected. YAN will be followed across the season; thus far, levels look good, with most samples approaching (or exceeding) 300 mg/L N. We are investigating observations of high pH relative to TSS in both central and northern VA samplings. Several pHs ranged from 3.3 - 3.6, and had correspondingly low TA and malic readings (TA average ~10.5 g/L; malic average ~7g/L). Data is being gathered from other areas of the state; based on limited sampling, this phenomenon has not been observed in the Shenandoah Valley region or similar sites at higher elevations.
More to come next week… the first samplings of Cabernet Franc are starting to arrive, and we’re looking forward to seeing their initial fruit chemistry!
(08/24/20)
Welcome to Virginia Tech Enology Extension's Website
Welcome! I'm Beth Chang, enology extension specialist for VCE/Virginia Tech. I collaborate with the analytical services lab and the viticulture extension team to support Virginia's grape growing and winemaking community. This website has been designed to facilitate communication on topics of interest and post updates regarding relevant events. In addition, there is information regarding other fantastic resources for both those in the industry and those simply looking to learn more about wine. To stay informed, please join our mailing list.
In the meantime, I'd love to hear from you! What content areas are you most eager to hear about? Please complete this super short survey (see below or click here); a few ideas are listed and there is the option to add specifics on desired material.
(05/01/20)