VOL. 2 / ISSUE 1
FALL 2015
WINEMAKER’S Q UA RT E R LY PRESENTED BY ETS LABS
- F E AT U R E Botrytis and Laccase in the vineyard -TESTING S e n s o r y Ta i n t s - N E W AT E T S Website updates
TABLE OF CONTENTS VOL. 2 ISSUE 1
FALL 2015
4
Questions and Answers
6
Sensory Taints
8
Botrytis and Laccase
12
Potential Alcohol
15
Harvest Scorpions
16
Our New Website
Editorial Team:
Owners: Gordon Burns, Marjorie Burns Creative Direction: Evin Morrison
Photography: Kingsley Burns, Evin Morrison
Editorial Contributors: Rich DeScenzo, Steve Price, Eric Herve, Gordon Burns, Marjorie Burns
Questions or feedback? Send us a note: editor@etslabs.com
A
s this issue goes to press, many of our West Coast clients are already well into harvest. Mother Nature has chosen to make her harvest visit earlier this year, ignoring some of your bottling schedules! This reminds us that grape growing and winemaking do not follow set scripts from vintage to vintage. To help understand Mother Nature this harvest, and bring out the best in what she has thrown your way, ETS has assembled and condensed a selection of our harvest campfire tales for you in this issue. We answer some of the most frequently asked harvest
questions on pages 4-5, and include useful information to help understand and manage potential vineyard taints on pages 6-7. You will also find an overview of Botrytis and a refresher on the challenges in predicting potential alcohol. Vintage 2015 marks ETS’ 38th harvest working in partnership with the wine industry. Our dedicated staff is working extended hours and weekends to ensure that your harvest needs are meet quickly and accurately. Thank you for allowing ETS to be an extension of your 2015 harvest team and to work with you again through this vintage. Gordon Burns (707) 302-1211 gburns@etslabs.com
Marjorie Burns (707) 302-1222 mburns@etslabs.com ETSLABS.COM
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Q&A We have compiled some of the most frequently asked questions we get in the lab and answered them for you here.
How can I tell what yeasts are in my fermentation?
My fermentation seems sluggish, how can I tell if the yeasts are alive?
DNA analysis can identify which yeasts are present; however DNA fingerprinting analysis takes it step further by differentiating between closely related strains of Saccharomyces cerevisiae. ETS Laboratories offers a method of DNA fingerprinting, known as Multi-Locus Variable Copy Number Tandem Repeat Analysis (VNTR). This method detects differences in the number of tandem repeat DNA sequences present in individual strains of yeast. While a single location DNA sequence may contain enough variation to distinguish between a few strains, multiple locations provide the potential to distinguish between unlimited numbers of strains making it a very powerful tool for evaluating the mixed floras commonly found during fermentation.
Historically, yeast viability has been measured using a semi-quantitative manual method with uptake of methylene blue and subsequent counting of the dead vs live yeast with a hemocytometer. ETS offers an automated, quantitative analysis for yeast viability, increasing accuracy and critical turnaround time in fermenting juices.
Winemakers choose which commercial yeast strains to use based on specific yeast attributes, including competitiveness and ability to finish fermentations. Yeast rehydration methods, must nutrient availability and fermentation parameters can result in less than favorable conditions for a specific commercial yeast strain, allowing indigenous yeast to flourish. Many winemakers would like to know which yeast are actually present and driving their fermentations, and how well they are performing.
Why use VNTR analysis? VNTR analysis enables the winemaker to see if the yeast used for inoculation actually dominates the fermentation. Changes in fermentation protocols can also be monitored to determine their impact on yeast performance. Native fermentations can have very diverse yeast populations that change dramatically during the course of fermentation. These population changes can be monitored and tracked with VNTR analysis. VNTR analysis has also been used by some wineries to identify and isolate new proprietary strains of vineyard-specific yeast that are competitive and capable of dominating fermentations.
4 |WINEMAKER’S QUARTERLY
Winemakers monitoring fermentation kinetics often want to take swift remedial action when they notice a fermentation slowing down or becoming sluggish. Sluggish fermentations may be a minor inconvenience, placing additional demands on winery resources and capacity, or they may become big problems, resulting in stuck fermentations and excessive production of volatile acidity. Many factors can contribute to reduced yeast viability and it is often difficult to determine the cause.
Our Beckman-Coulter Vi-CELL XR analyzer utilizes and automates the widely accepted Trypan Blue Dye exclusion method. When yeast cells die, their membranes become permeable allowing the uptake of the trypan blue dye. As a result, the dead or non-viable cells become darker than the viable cells that do not absorb the dye. This contrast is what is measured in order to determine viability. Yeast cells pass through the flow cell of the analyzer and are counted, providing measurements of total cell count and percent viability. Yeast viability results in the 70-90% viable range are indicative of a strong fermentation. When viability drops below 50%, it often indicates a stressed yeast population that is in decline. Vi-Cell analysis can be run directly on samples with a yeast cell count range of 1,000 to 10,000,000 cells per mL and provides same-day, rapid-turnaround results for yeast viability. Although the ETS yeast viability analysis provides a measurement of percent viable yeast, it is not sensitive enough to use as a check for bottle sterility. Likewise, the procedure does not identify or differentiate which yeast strains or species are present in a sample.
My fermenting juice smells like rotten eggs. What should I do?
The rotten egg odor that sometimes occurs during fermentations is caused by the most frequently found volatile sulfur compound in fermenting juice, hydrogen sulfide (H2S). H2S is highly reactive, interacting with alcohols to form foul-smelling mercaptans (R-SH). When mercaptans are present, oxidative conditions, either intentionally created to dissipate H2S (aeration/splashing), or occurring unintentionally, can result in the formation of disulfides (R-S-S-R). Since disulfides have a much weaker odor than mercaptans, the offodor seems fixed. However, disulfides can revert back to mercaptans in the reductive bottled wine environment, causing a recurrence of the off sulfide odor. There is some concern that closures with low oxygen transfer rate (e.g. screw caps) may exacerbate this problem. If H2S production seems excessive during active fermentation, it is most likely due to yeast stress. In some cases, yeast stress can be reduced by adding a quickly available source of nitrogen. If H2S has been a problem during fermentation there will almost certainly be mercaptans present also. Consequently, once the fermentation is completed, aeration becomes an even more risky option due to increased risk of disulfide formation. Copper additions can remediate wines tainted with H2S and mercaptans, but are not effective in removing disulfides. Ascorbic acid treatment prior to copper addition may be effective in splitting disulfides back into the more treatable mercaptan form. It is critical to ensure sufficient levels of free SO2 are present before making either copper or ascorbic acid additions. The amount of copper needed to remove H2S or mercaptans cannot be predicted based on sulfide concentration. Benchtop fining trials with sensory analysis can be used to determine the minimum concentration of copper necessary, since residual copper levels cannot exceed 0.5 mg/L and levels greater than 0.2-0.3 mg/L can cause instability. Copper treatment may also be detrimental to varietal and fruity aromas in whites and rosés.
I’ve never used phenolic analysis. How can I get usable information this season? Getting started with phenolic analysis involves establishing target values, particularly for tannin. The easiest way to do this is to work with wines you already know. Generally winemakers have strong opinions about wines they have made. Analyzing a set of recent production lots or finished wines from recent vintages will give you tannin values that you can relate back to recent successful or not-so-successful wines. Which of those wines was the most successful in terms of body, mouthfeel and astringency? What were their tannin values? Which wines were too soft, too harsh, or too astringent? How high was the tannin value in those wines? This concept can also be applied to other producers’ wines. How do the tannin values of your wines compare to other producers’ wines that you like or don’t like? Answering these questions can give you a target range for tannin during the coming season. Once a target is established, keep refining it. How does acidity or alcohol interact with tannin impressions? Should target tannin values shift with the vintage? Is higher tannin more appropriate in a warmer vintage? What about tannin quality? How much “seediness” (catechin levels) do you tolerate? Do you prefer medium or high ratios of polymeric anthocyanins/tannin? Many analytes have clearly defined limits of good or bad – phenolic compounds do not. There are no absolute right answers. The correct tannin value for a wine is the one that matches the wine style you are trying to make. Find a style you like, find out what phenolic values are associated with that style, and then you can fine-tune your winemaking to achieve that style consistently. *To help in forming and implementing a phenolics analysis plan, call our phenolics expert Dr. Steve Price at 541-908-4279 or email sprice@etslabs.com. We’re always available to help you understand your phenolics results and suggest practical steps to make real and constructive changes in your grape growing and winemaking. ETSLABS.COM|
5
TAINTS VINEYARD FROM THE
Over the years, ETS has helped identify and analyze sensory taints in wines, some of which can originate in the vineyard. While not all taints are considered undesirable, it is important to understand and know the levels of these sensory compounds in order to prevent them from negatively affecting your finished product.
Smoke Taint
Smoke taint is caused by smoke compounds, mainly volatile phenols, which are absorbed by vines and end up in wine. They cause off-odors and flavors described as “burnt”, “smoked fish”, “salami”, and “ashtray”. Research in Australia has shown that smoke phenols, once absorbed by vines, are largely bound to sugars (glycosylated). It is difficult to detect smoke taint with sensory evaluation of the fruit since glycosylation renders smoke phenols odorless, causing smoke taint in grapes to go largely unnoticed. Smoke taint typically manifests itself during fermentation when some of the odorless glycosylated phenols are quickly hydrolyzed back to the active odor forms. Laboratory analysis can measure trace levels of free guaiacol and 4-methylguaiacol, the primary indicators of smoke taint, in grapes even if they are below the sensory threshold, giving winemakers a tool to screen fruit and take early corrective action whenever possible.
6 |WINEMAKER’S QUARTERLY
Smoke phenols are readily transferred from grape skins and vine MOG (material other than grape) into the juice and fermentation. Efforts to mitigate smoke taint in white wines focus on minimizing skin contact, and are highly dependent on harvest parameters and winemaking techniques. Minimizing skin contact during red winemaking is not practicable, however, so mitigation options for red wines are limited and often disappointing. When smoke taint is suspected in a wine, determination of guaiacol and 4-methylguaiacol levels can confirm the presence of taint and its intensity. When considering treatments, knowing the baseline levels of these compounds will give you a starting point for comparison with results after treatment, allowing you to confirm its efficacy.
IBMP
IBMP (2-Isobutyl-3-methoxypyrazine) is the main compound responsible for the “green bell pepper” aroma in wine. In Sauvignon Blanc, the compound adds an often desired “grassy” character. In red wines however, this flavor is largely unpopular. Excessive IBMP levels in red wines, typically Cabernets or Cabernet-based blends, can lead to disappointing ratings and mixed success in the marketplace. Because IBMP levels typically decrease as grapes mature, monitoring IBMP throughout ripening gives winemakers a unique tool to assess “aromatic maturity” along with berry maturity to target harvest dates based on their desired wine style. It is now believed that the IBMP decrease during ripening is caused by an active metabolic process, instead of degradation by sunlight. There is strong evidence that severe hydric and/or heat stress can trigger “maturity stops”, where IBMP degradation suddenly halts. This can result in shriveled, high-brix
Eucalyptol
Eucalyptus character is one of the industry’s most controversial aromas. On one hand, Eucalyptus traits are considered desirable in some “cult” wines; on the other hand, in excess this character can be overwhelming. ETS researched eucalyptol (1, 8-cineole) in wine, and discovered airborne transfer from eucalyptus trees growing near vineyards to grape berries. Eucalyptol can adhere to the wax on berry surfaces, and is then transferred into wine during extended macerations and fermentation on the skins. Eucalyptus character is rarely found in white wines due to minimal skin contact and extraction during production. The Australian Wine Research Institute also found that eucalyptol can be transferred through vine leaves and petioles, MOG, and from eucalyptus leaves and nuts that may end up in harvested grapes.
Invasive Insects
Ladybug taint first came to light in Ontario in 2001. Offensive off-aromas (described as vegetal, peanut, bell pepper, and asparagus) were often noticed in wines following a population explosion of Multicolored Asian Ladybeetles (MALB), originally introduced for biocontrol of aphids. Researchers at Brock University in Ontario traced the off-aromas to IPMP (2-isopropyl3-methoxypyrazine) released by the ladybugs when they were crushed during the winemaking process. As little as one beetle per vine may be sufficient to taint the resulting wine. Ladybug Taint appears to be a reoccurring problem on the east coast of the US, but so far has not had a significant impact on the west coast.
Photo: Thom Quine
raisins with concentrated IBMP, and cause discordant combinations of “green/herbaceous/unripe” and “jammy/overripe” flavors. Monitoring IBMP from the early stages of the ripening process provides a starting point to improve fruit quality from underperforming vineyards. Vineyard management decisions such as trellis types, fertilization, water availability, and early leaf removal are known to have a significant impact on IBMP. Once you have a better understanding of the kinetics of IBMP accumulation and degradation in a problem site, you can modify viticultural practices, and measure the impact in the following years. Testing grapes just prior to harvest is a useful tool for predicting IBMP levels in the resulting wine, since grapes do not contain any precursors or “hidden” sources of IBMP, and IBMP levels are not easily altered by standard winemaking processes.
Flavors perceived during tasting change with varying concentrations of eucalyptol. Trace levels close to 1 ppb are associated with “fresh”, slightly “minty” notes. In the low ppb range, “minty” or “fresh bayleaf ” aromas become stronger, and more easily identifiable as eucalyptus as concentrations increase. Wines with strong eucalyptus odors may contain more than 20 ppb of eucalyptol. Analysis of eucalyptol enables winemakers to objectively confirm and document their sensory impressions. It can also be used to assess the impact of eucalyptus trees near vineyards and the influence of winemaking practices such as fruit sorting at harvest. Winemakers can also minimize or maintain consistent levels of eucalyptus character by measuring eucalyptol concentrations in wine lots before blending.
released by these bugs may also taint wine. These odor compounds, identified in 2010 as unsaturated aldehydes by the University of Maryland, possess a “skunky”, “citrusy”, or “piney” odor, reminiscent of fresh cilantro. Preliminary research at Oregon State University in 2013 suggests that wines may become tainted at an infestation level of only a couple of bugs per vine. There is concern that Pinot Noir might be especially susceptible to the taint.
Another insect, the brown marmorated stink bug (BMSB) is an exotic species native to Asia that is now found in most of the US. Populations are established in Washington and Oregon, with occasional sightings in California. There are concerns that odor compounds
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7
Botrytis cinerea
friend or foe?
8 |WINEMAKER’S QUARTERLY
Botrytis cinerea is a fungal pathogen that can be the instigator of, or a primary component of bunch rot in grapes, as well as responsible for Noble Rot. Unless you are intentionally producing wines from Botrytis-infected grapes, such as a Sauterne style, Botrytis is considered a problem. Botrytis can infect damaged or healthy fruit and is often the first microbe to infect the grapes, followed by other fungi, yeast and bacteria. Botrytis-infected grapes are regarded as undesirable for the production of table wines because of problems with high microbial load, as well as problems associated with laccase activity and presence of glucans. Wine grape growing regions impacted by Botrytis generally try to minimize impact of the fungus by using fungicide applications, minimizing damage to fruit, and reducing the incidence and duration of wetness events. Viticultural treatments to increase air flow, such as leaf removal and cluster thinning can help reduce the incidence of disease. >> Continue
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BOTRYTIS INFECTION Botrytis spores are disseminated by rain splash or wind and deposited on the vine surfaces. Once the spores germinate on the fruit, they begin the process of skin surface penetration to obtain nutrients from the underlying cells. Botrytis is an opportunistic pathogen and can infect damaged or dead plant tissue, as well as healthy tissue. Two types of disease progression are observed: the early/latent infection and the late, more common type of infection. Early or latent infection occurs during grape flowering when conditions are conducive to spreading spores.
Spores landing on the young flowers are capable of infecting the plant, and then becoming dormant. There are no easily visible symptoms during dormancy, and grape development appears relatively normal. The fungus becomes active again prior to veraison, when the first visible symptoms start to develop. The fungus begins to produce and release visible spores that can result in secondary infection in clusters on the same and adjacent vines prior to harvest.
The late or more common type of infection can result from the release of spores from the latent infection, or from rain dispersal of spores from various contaminated sources in the vineyard. Typical symptoms of this form of the disease involve obvious discoloration and shriveling of berries in a cluster, with production of gray spores on the surface of the infected fruit.
PROBLEMS ASSOCIATED WITH BOTRYTIS INFECTION There are several problems associated with making wine containing Botrytis-infected grapes. The most common are phenolic oxidation due to laccase activity on juice/wine
constituents and clarification/filtration issues due to excess polysaccharides such as glucan and pectin. In addition, elevated levels of glycerol and gluconic acid are often associated
with Botrytis infection. These compounds can be metabolized by bacteria, causing a negative sensory impact from formation of acrolein and/or volatile acidity.
“ Botrytis can infect damaged or healthy fruit and is often the first microbe to infect the grapes, followed by other fungi, yeast and bacteria.” LACCASE Laccase produced by Botrytis cinerea causes a number of problems in the juice and wine. Laccase oxidizes phenolic acids, converting them to the quinone form which can further drive non-specific oxidative reactions. Oxidation of juice constituents can affect aroma, flavor, and stability. Once the quinones oxidize the juice constituents, they are simultaneously reduced back to their original hydroxycinnamic acid form. Oxidation of flavanols by caftaric acid quinone can result in polymerization of the quinones, forming a brown pigmented discoloration of the wines that eventually
precipitates. Lastly, caftaric acid quinone can combine with glutathione to form Grape Reaction Product, potentially changing mouthfeel in white wines. Botrytis laccase activity has an optimum pH of 3.5 and temperature of 60C. Botrytis can produce different forms of laccase that are active against different types of phenolic compounds. These different forms are induced by various plant defense responses and multiple forms can be produced by a single fungal strain. Laccase production varies from strain to strain
and may be limited due to the number of isoforms produced or the specific plant/fungal strain interaction. ETS has observed levels of laccase activity in juice and wine ranging from less than 1 unit/ mL to a high of 106 units/mL. Although it is difficult to determine what level of risk is associated with laccase in individual wines, the generalized guidelines in the table below provide a good starting point.
WHAT LEVELS OF LACCASE REPRESENT A POTENTIAL RISK TO WINE? RED WINE
WHITE WINE
< 5 unit
1 unit
PROACTIVE TREATMENT
5-15 units
2-5 units
AGGRESSIVE TREATMENT
>15 units
> 5 units
CAUTION
Two different models of laccase “evolution” were observed in the 2011 Harvest. The first model was observed in heavily compromised fruit (what some people call a “slipskin” level of
10 | WINEMAKER’S QUARTERLY
infection) and the second model was observed in fruit that appeared relatively clean, with low levels of visible infection. The first model, with the highest apparent level of infection, was
easier to remediate than the second model with the lower apparent levels of infection.
Overall, many wineries were proactive when handling heavily compromised fruit, whereas less effort was put into mitigating the effects of laccase on the relatively clean fruit.
HEAVILY COMPROMISED FRUIT MODEL RELATIVELY CLEAN FRUIT MODEL
The amount and duration of laccase activity found in wine produced from relatively clean fruit suggests that it is as important to proactively treat the relatively clean fruit as it is to treat the
more damaged fruit. At the very least, separate free run from pressed wine as the press fractions can contain high levels of laccase.
LACCASE LEVELS POST CRUSHER
EFFICACY OF TANNIN TREATMENTS
LACCASE INCREASE DURING FERMENTATION
LACCASE AFTER PRESS
High
50-100% in 48 hours
No Significant Increase
Small or No Increase
Low
10-40% initial drop
Continuous Increase/ Presence
Large Increase
TREATMENT OPTIONS Laccase is a protein and winemakers can take advantage of tannin-protein interactions to reduce levels of laccase in a wine. There are a large number of enological tannins available to the wine industry. Tannin vendors know their specific products and should be able to provide information regarding the most appropriate tannin product for laccase removal. In many of the heavily compromised fruit samples, 200-400 ppm of tannin added at the crusher resulted in an 80-100% reduction in laccase activity within 48 hours. Bentonite can be effective for removal of laccase but its’ efficacy is dependent on the juice pH and the net positive charge of the individual laccase isoforms.
In the relatively clean fruit model, laccase is trapped in the grapes and slowly released during fermentation. Recommended treatment of these grapes include broad spectrum polysaccharide degrading enzymes, containing pectolytic activity, which can effectively release the “trapped” laccase for interaction with enological tannins. Enzyme vendors should be able to make recommendations regarding which commercial enzyme preparations are the most appropriate for this application. SO2 is an important tool when mitigating the effects of laccase. As long as there is active laccase in the juice, oxidative damage is occurring. Discoloration of the wine as well as other negative attributes associated with Botrytis
can be delayed with adequate concentrations of SO2. Clients often ask if there are any methods to inactivate laccase. Heat inactivation of the laccase enzyme, using either flash détente or pasteurization, results in juices with no detectable laccase activity. Another method to inactivate laccase involves the use of specific acid proteases that are capable of proteolytic activity under the extremes of pH and ethanol found in many wines. These proteases cleave the laccase protein into smaller, non-functional peptides.
OTHER BOTRYTIS-RELATED PROBLEMS Laccase mediated oxidative damage is not the only problem associated with wines made from Botrytis infected grapes. Botrytis infections cause the enzymatic degradation of grape cell walls as well as production of the extracellular polysaccharide, glucan, which can cause settling and filtration issues. Botrytis induced glucan production varies by strain, with some strains producing relatively elevated amounts compared to others. Research indicates that the presence of as little as 1 mg/L in wine can cause filtration problems. Glucans produced by Botrytis can be degraded
by treatment with β-Glucanase enzymes. This can be done at the juice stage, or later with the finished wine. Glucans are secreted by Botrytis in the skin, between the cuticle and the pulp of the berries. Mechanical treatments resulting in physical damage to the grape skins can result in larger amounts of glucan released into the wine. Care should be taken when processing fermentations with grapes known to be infected with Botrytis to minimize problems with glucans. Glucans are not the only polysaccharidebased problem with wines made from Botrytis-
infected grapes. Botrytis produces pectolytic and cellulolytic enzymes that create a different polysaccharide profile from non-infected grapes. Wines produced from Botrytis infected grapes contain higher levels of polysaccharides than wines obtained from non-infected grapes, which in turn can cause problems with fouling during filtration. Polysaccharide problems are often hard to identify, although difficulty or delayed clarification may be an indication. Elevated levels of polysaccharides in a wine can often be detected using an ethanol-based pectin precipitation test.
CONCLUSION Making wine with Botrytis-infected grapes can result in a number of subsequent problems. However, understanding the basis for these problems and addressing them individually can mitigate the potential negative impact they can have on a wine.
infected, or suspected of being infected, with Botrytis cinerea should be analyzed for laccase activity and treated accordingly. Wines made from Botrytis infected grapes, and still containing active laccase, should be maintained in a reductive state to minimize browning and discoloration, and should not be blended with Early detection of laccase enables winemakers wines that do not contain laccase. to take appropriate actions to minimize the impact on the final wine product. Grapes
Problems with settling or clarification may indicate elevated levels of glucans and other polysaccharides are present in the wine. Confirmation of their presence can help in determining appropriate treatments. Treatment with broad spectrum polysaccharide degrading enzymes, often labeled as filtration enhancing enzymes, can accelerate settling and prevent problems at filtration.
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11
POTENTIAL ALCOHOL Knowing the amount of fermentable sugar in juice and its conversion rate into alcohol allows winemakers to predict the potential alcohol level in their wines. This sounds quite simple in principle, but there is more than one way to measure “sugar”, and formulas to convert this sugar into potential alcohol often miss the mark.
Old School Style: “°Brix x 0.6” °Brix is commonly used as a measure of sugar in grape juice and must and is expressed as a percentage by weight (% w/w). One degree Brix is defined as 1 gram of sucrose in 100 grams of aqueous solution. However, grape juice does not naturally contain sucrose, but rather glucose and fructose and a variety of organic acids and other dissolved solids. So when used for grape juice, °Brix is actually just an approximation of dissolved sugar.
12 | WINEMAKER’S QUARTERLY
So while ºBrix can provide a quick estimate of sugar content, it is not an accurate representation of the fermentable sugars, and using ºBrix for estimating potential alcohol adds an additional layer of uncertainty to alcohol predictions. Differences between ºBrix and actual fermentable sugar content are even more pronounced in high ºBrix fruit and in fruit affected by fungal growth. How ºBrix is measured also has an influence. Differences exist between ºBrix by refractometry (historically the most common method), densitometry (using either hydrometers or digital instruments), and other secondary measurements. The differences among the various measurement techniques are quite unpredictable depending on sample composition. Proper sample preparation matters, too: in our lab, juices are centrifuged before analysis, and then gently mixed by inversion to avoid stratification, to ensure the most accurate results. Particulates have a minimal impact on refractometry, but their impact might be more significant on densitometry results.
(Glucose + Fructose) / 17 Using glucose + fructose analysis to predict potential alcohol provides a more accurate measurement of the levels of fermentable sugar compared to using ºBrix. Note that in ripe fruit, glucose + fructose numbers often appear higher than the corresponding ºBrix results. The reason for this is that ºBrix is measured as a percentage by weight, meaning ºBrix values are greatly influenced by the density of the juice, while glucose + fructose is measured as weight by volume and is independent of juice density. An official conversion rate formula used in Europe is: Potential Alcohol (% vol) = glucose + fructose (g/L) / 16.83. In practice, rounding the 16.83 conversion factor to 17 is common.
The Reality While client feedback suggests that glucose + fructose values improve the quality of their predictions, it is important to remember that yeast populations and fermentation conditions
may vary, and any prediction of potential alcohol is only an approximation. Alcohol conversion ratios are always subject to variability, so it is possible your actual alcohol may be lower or higher than the estimate. Many clients have found that the conversion rates observed for their own yeasts and fermentation conditions generally remain relatively constant, and use their internally observed historical conversion rates to calculate potential alcohol content based on their glucose + fructose values. With white wines, predictions are usually fairly accurate. When making red wine, however, using a truly representative juice sample can be a challenge and can affect potential alcohol predictions. A juice sample taken soon after a tank is filled may not take into account un-popped berries, often unripe (containing less sugar and more acids) and raisins (sometimes an overlooked source of large amounts of sugar, acid and potassium). We suggest sampling after an initial 10°Brix drop, and analyzing the fermenting sample for glucose + fructose and alcohol simultaneously for a more accurate potential alcohol estimate.
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13
HARVEST
SCORPIONS
w
ith harvest upon us, itâ&#x20AC;&#x2122;s prudent to think about what indigenous microbes the grapes may be bringing into your winery. The ETS Juice Scorpion Panels provide a tool to help winemakers understand one of the important entry routes into the winery for specific spoilage organisms.
Identifying and quantifying yeast and bacteria that can cause spoilage during the winemaking process is the first step in preventing these spoilage problems. Specifically, this information can provide the winemaker with a situational awareness for potential problems that can occur during the cold soak process, in stuck or sluggish fermentations, or later during wine aging. The Scorpions Juice Yeast Panel detects several species of Hanseniaspora, Pichia, Zygosaccharomyces, Brettanomyces and Saccharomyces. The Scorpions Juice Bacteria Panel detects several species of Acetic Acid bacteria, Lactobacillus, Pediococcus, and Oenococcus oeni. The Scorpions Juice Combined panel detects all of the yeast and bacteria from both panels. Elevated levels of microbes such as the wild yeasts, Hanseniaspora and Pichia, can result in production of volatile acidity and ethyl acetate, having a negative sensory impact on the wine. In addition, large populations of wild yeast can deplete the YAN in the must, resulting in a YAN deficiency
for the Saccharomyces cerevisiae driving the fermentation. Detection of high levels of Hanseniaspora or Pichia in a must should be sufficient to trigger a YAN recheck prior to yeast inoculation, followed by YAN supplementation if necessary. Likewise, the presence of heterofermentative lactic acid bacteria, such as Lactobacillus brevis, L. kunkeei, L. hilgardii, L. fermentum, and Oenococcus oeni, in a juice would call for increased monitoring of malic acid and microbial levels if the fermentation becomes sluggish or stuck. Early identification of the presence of these bacteria and recognition of the risk they pose to difficult fermentations is the first step in preventing VA formation in stuck fermentations. Winemakers understand that the juice chemistry has a major impact on the wine chemistry and microbiology. In a similar manner, juice microbiology can influence wine microbiology and chemistry. Large numbers of Acetic Acid bacteria on incoming fruit can carry through the fermentation and cause problems with VA production during wine aging in the barrel. Overall, knowing which microbes are coming in on the grapes provides the winemaker with an early warning to potential problems that could occur throughout the winemaking process, enabling proactive and early intervention to minimize spoilage risks.
ORGANISMS TESTED
VOLUME
CONTAINER TYPE
TARGET TURNAROUND
PRICE
60 mL
Standard ETS sample tube
2 working days
$60
60 mL
Standard ETS sample tube
2 working days
$60
60 mL
Standard ETS sample tube
2 working days
$120
Brettanomyces bruxellensis Yeast Panel
Saccharomyces cerevisiae Zygosaccharomyces bailii Acetic acid bacteria Lactobacillus brevis/hilgardii/fermentum Lactobacillus casei/paracasei/mali/nagelii
Bacteria Panel
Lactobacillus kunkeei Lactobacillus plantarum Oenococcus Pediococcus
Combined Panel Includes all organisms from both yeast and bacteria panels
14 | WINEMAKERâ&#x20AC;&#x2122;S QUARTERLY
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