VOL. 3 / ISSUE 2
WINEMAKER’S Q UA RT E R LY PRESENTED BY ETS LABS
- F E AT U R E Quercetin in Wine -IN THE LAB The science of oak aromas in wine
TABLE OF CONTENTS VOL. 3 ISSUE 2
04 06 09 10
Questions and Answers
Oak Aromas
The ETS Team
Quercetin "Slime"
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
W
inter has come and gone and with the vines starting to bud, we're well on our way to spring. As always, we hope you had a successful harvest and then a well-deserved, restful break. In this issue, we're taking a deeper look inside oak – breaking down the range of aromas that are transferred into wine. We share the science that helps shape "oaky aromas", including the impact of yeast, oxygenation, and typical practices for red and white winemaking. This Quarterly also gives us a great opportunity to share new information with winemakers across the country - especially those who can't make it to our educational seminars. Our main article looks at the phenomenon of "slime" that some winemakers have unfortunately discovered in the bottle. Steve Price, our phenolics specialist, shared research on these strange quercetin precipitates at a recent seminar, and we've put it here in written form. As always, feel free to reach out to us with any questions - we're happy to help! Gordon Burns (707) 302-1211 gburns@etslabs.com
Marjorie Burns (707) 302-1222 mburns@etslabs.com
Q& A
4 |WINEMAKER’S QUARTERLY
Q
What does ISO-accredited mean and why is it important?
In the winemaking process, quality analytical results validate sensory impressions and are essential to enable your sound winemaking decisions. It is important to realize that not all data is created equal. In order for analytical results to have any value to a winemaker, they have to be unquestionably reliable and accurate.
A Q
Laboratory accreditation, (on top of a comprehensive quality assurance system), provides a means of evaluating the competence of laboratories to perform specific types of testing. A lab’s scope of accreditation lists the specific analyses that have been evaluated by specialist technical assessors as part of the accreditation process. ETS offers over 40 accredited analyses using 17 technologies. Our quality systems and ISO-accreditations enable us to provide the most reliable numbers in the industry. Our continuing education and training programs lead to a technically competent team, while our calibration, testing and validation processes provide you with data that you can trust. Our labs are also regularly audited by a third party to deliver data worthy of the fine wines you craft.
Can Brettanomyces have an influence on the oak aroma characteristics in my wine?
Brettanomyces can influence perceived oak characters via possible adsorption of compounds on cell walls, absorption and metabolism of oak aroma compounds, and by the release of 4-ethylphenol (4EP) and 4-ethylguaiacol (4EG).
A
Generally, 4EP and 4EG have a masking effect on wine aromas. On the other hand, the chemical similarities of 4EP and 4EG with the spicy/smoky volatile phenols produced from oak toasting may result in additive sensory effects and perception. Periodic monitoring of Brettanomyces activity with 4EP/4EG and/or ScorpionsÂŽ analysis is recommended during oak aging. When submitting samples for the oak aroma panel, checking 4EP/4EG levels makes sense due to their interactions with oak aroma compounds, especially when results will be compared to sensory evaluation data.
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INSIDE the Oak
Dissecting Oak Aroma Aromas from oak aging are an integral part of many fine wines. Our modern understanding of oak aroma chemistry is rooted in research from the late ‘90s, when scientists helped identify more than 70 volatile compounds that play a role in oak’s contribution to wine aroma. The exact chemical makeup of a wine’s oak profile varies with the oak species and origin, cooperage practices, and winemaking techniques – but the research team at ETS selected nine key compounds that can be used to accurately represent the broad range of chemical classes and sensory effects that make up the overall oak aroma:
Compounds and their sensory effects:
Eugenol & Isoeugenol
Oak Lactones (cis- and trans-)
Furfural & 5-Methylfurfural
Fresh Oak and Coconut
Sweet, Butterscotch
Vanillin
Guaiacol & 4-Methlyguaiacol
Vanilla
Smoke, char, and spice
Clove and Spice
Yeast Impacts on Oak Aroma During barrel fermentation, a large part of the aldehydes extracted from oak, such as vanillin and furfurals, are converted into non-aromatic alcohols. The aroma molecules can also bind to yeast’s cell walls or wine macromolecules like polysaccharides and polyphenols – both during and after fermentation. This helps to explain what is often called the “integration” of oak aromas in a wine.
The interactions between yeast and oak compounds can extend further than aroma. The macromolecules (mannoproteins) released by yeast can add “volume” to a wine’s mouthfeel, and also bind with oak ellagitannins, decreasing astringency. Lees also have an antioxidant effect; they contribute glutathione, which can help to protect the most fragile aromas and improve aging potential.
The Influence of Oxygen Barrel fermentation and aging naturally causes a microoxygenation of wine. Oxygen transferred through the barrel first reacts with phenolic compounds (catechols), forming quinones and hydrogen peroxide (H2O2). The H2O2 can then oxidize ethanol, creating acetaldehyde.
In red wines, acetaldehyde (and other aldehydes such as furfurals) triggers important tannin modifications, especially the formation of tannin-anthocyanin complexes. These complexes have been long known to promote color stability, but also seem to be associated with a softer mouthfeel.
White Winemaking in New Barrels The traditional Burgundy method for white winemaking was rediscovered in the late ‘80s. It has since been widely accepted and has provided ample demonstration that alcoholic and malolactic fermentations in barrels can tame and integrate oak character. (As compared to late barreling – after fermentation and racking off lees – which can often lead to excessive oak character.)
An important part of this technique is lees stirring (batonnage), which helps the release of desirable compounds from yeast, facilitates their interaction with wine components, and prevents the risk of sulfide off-odors.
Typical Evolution of Red Winemaking in New Barrels Even though this phenomenon is less pronounced than with white wines, barreling “clean” red wine can lead to overpowering oak aromas and a more “angular” structure. Many winemakers have found that barreling progressively “dirtier” wine can be better. When barreling wine before malolactic fermentation, many winemakers have found that the
oak aromas become more “integrated” in the wine. Also, tannins are described as “fuller”, “softer” or more “velvety.” Taking this logic to the extreme, many experiment with red wine fermentations in the barrel, despite the significant need for additional manpower.
Influence on winemaking Winemakers use insights into oak aroma compounds throughout the winemaking process to enhance their finished product: • Evaluating barrel trials (wood source, toast level, cooper)
French Oak MT
• Monitoring wine aging in barrel (evaluation of the same wine over time) • Fine-tuning barrel management (effects of barrel age or sanitation programs) • Evaluating or managing barrel alternatives (staves, chips, beans) • Comparisons to benchmark or competitors' wines When evaluating a barrel trial, winemakers usually take a single wine and age it in barrels of various origins to compare aroma differences. In addition to in-house sensory evaluation by the winemaking team, oak aroma analysis can help quantify differences between different varieties and toast levels, and even highlight the “house styles” of various cooperages.
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WINEMAKER’S QUARTERLY
American Oak
BEHIND THE NU MB E R S MARI A GALLEGOS
JOINED ETS
1988
POSITION
“ There's always
Analyst & Trainer
E T S L O C AT I O N
St. Helena, CA
something new to learn.
”
When you work with ETS, we deliver more than just numbers on a lab report. We connect you to a dedicated team of researchers, scientists, and technical experts who guide you in making key strategic decisions, helping turn those numbers into valuable insights. The ETS team is the most knowledgeable, dedicated, and talented in the industry. Some of us have worked closely with you over the years, while others have worked tirelessly behind the scenes to make sure we support your winemaking endeavors with innovative tools and uncompromising quality. In this column, we'll share some of the stories and faces behind your lab reports.
MARIA GALLEGOS has seen it all. As one of the first employees at ETS, she was there as our laboratory grew to support the expanding local wine industry, and her duties have grown alongside it. Maria first joined the ETS team in 1988 as a housekeeper. Her husband worked at Conn Valley vineyards for Gus Anderson, who knew Maria was looking for a job and referred her to ETS.
project, Maria saw some samples waiting to be processed and tried her hand at lab work. "I would watch Gordon do the dilutions for the gas chromatograph," she said, "so I went over and prepared the samples and injected it into the GC." "Gordon said: 'good for you', " Maria recalls. From then on, she began formal training and qualification on lab techniques and helping with sample preparation, When she started at ETS, Maria and ETS sent her to computer had just moved to the U.S., and only classes at Napa College. "I'm not spoke Spanish. "It was hard at first," a conformist," says Maria, "I don't says Maria, "because we couldn't wait for someone to give it to me – communicate." ETS owners Gordon I go for it, and I got it." and Marjorie helped enroll her in an English class that she attended in In the twenty-nine years since the mornings before coming to work. Maria has continued to take Learning was a priority for Maria, on new responsibilities as the who was determined to grow her skills. capabilities at ETS have grown. "In my village, girls didn't go to school Today, Maria serves as one of the past the 6th grade - the fathers didn't main trainers for new analysts. She allow it," she said. "But when I came teaches them methods and procedures to the U.S.A., I knew I wanted to grow for auto chemistry analysis and sample up and do something professional." handling. "There's always something new to learn," explains Maria, but Although she started as a housekeeper, she still relies on the techniques she Maria was always paying attention picked up in those early years: "the to the work going on around her in instruments today are faster, but the the lab. One day, while Marjorie and basics are still the same." Gordon were focused on another
Maria is about to celebrate her 30year anniversary on the ETS staff and is looking forward to many more years in the lab before taking a well-deserved retirement and spending time back in her village, El Llano Michoacan. "I feel like I achieved my dream," she says, before offering some advice for the generation that will follow her: "if you want to do something, do it with passion, with heart – not just to do a job."
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Quercetin in
Wine Qu erc etin prec ipitates in red win es are a n u nc omm o n but par tic ul arl y tro uble s om e problem. Prec ipitates fo rm in bottl e d wi n e s u su all y after a win e is o n the m arket. A l th ou g h qu erc et i n is a n atural l y o c c urrin g c omp ou n d , i t s preci pitates c an fo rm ugl y green ish cl u mp s t hat look fo reign in win e. Bottl e prec i p i tate s of qu erc etin have res ul ted in expen si ve wi n e rec al l s an d re-bottl in gs .
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The problem is most common in Sangiovese and any winery making Sangiovese should be aware of the problem and have a proactive program to avoid quercetin precipitates. However it may also be a problem in other varieties. We have seen quercetin precipitates in Merlot, Pinot Noir, Grenache, Chardonnay and even cranberry wine. The number of quercetin-related problem
wines received at ETS seems to be increasing in the last two years and there may be a connection to recent warm vintages. The two keys to the issue are the effects of glycosides, or sugars on solubility and the colloidal structures formed from phenolic compounds in wine.
Flavonols in Grapes
Phenolic nomenclature is always confusing and there are a few points of possible confusion in this article. Flavonols are different from flavanols! Flavanols are one of the names for catechins or flavan-3-ols associated with seed phenolics and tannin sub-units.
Flavonols are naturally occurring compounds synthesized in grape skins to protect grape berry tissue from ultraviolet light. They are formed throughout berry development, starting right after bloom. Four flavonol glycosides are present in grapes: quercetin, myricetin, kaempferol and iso-rhamnetin with quercetin glycosides always having the highest concentrations. Glycosides are chemical compounds with sugars attached. The main sugars attached to flavonols in grapes are glucose, galactose and glucuronide. Concentrations of flavonols in grapes are influenced by cluster sun exposure, cluster morphology, berry size and genetic factors (some grape varieties produce more than others). Flavonol glycoside concentrations are highest in grapes with open canopies, loose clusters, and small berries.
Flavonols can be either glycosides or aglycones: glycoside = with a sugar, aglycone = without a sugar. On its own, the name quercetin refers to the aglycone.
OH OH
Extraction and Hydrolysis
HO
During fermentation and maceration of red wines, flavonol glycosides are rapidly extracted from grape skins. Extraction curves generally follow anthocyanin extraction kinetics with most extraction occurring within a few days of the start of fermentation. The extractability and solubility of the flavonol glycosides are enhanced due to their attached sugar.
O
O OH
O
OH
O
HO
HO OH
OH OH
HO
O
OH OH 12 | WINEMAKER’S QUARTERLY
O
During fermentation and aging flavonol glycosides may lose their attached sugar. This hydrolysis results in a release of flavonol aglycones (flavonols without an attached sugar). There are two mechanisms of hydrolysis. An enzymatic hydrolysis may result if glycosidase enzymes are present. These enzymes can cleave sugars off a wide range of chemical compounds. Some yeasts and microorganisms have glycosidase activity and commercial enzyme preparations used as extraction aids may also have some glycosidase activity. Enzymatic hydrolysis is fairly rapid but usually only occurs during fermentation and maceration. All of the flavonols may be converted from glycosides to aglycones in the presence of high enzyme concentrations. A slower acid hydrolysis also converts flavonol glycosides to aglycones. This hydrolysis is not enzymatic. It starts during fermentation and continues during storage and aging in tanks, barrels and bottles. It is the acid hydrolysis that is the root of the problem in most quercetin bottle precipitations.
Solubility Flavonol aglycones are considerably less soluble than their glycosides. The solubility of quercetin glucoside in water is over 120 mg/L. Under the same conditions, the solubility of quercetin is less than 1 mg/L. The solubility of flavonol aglycones in red wine is dependent on other wine components. Phenolic compounds, particularly anthocyanins and tannins, appear to act as co-factors increasing the amount of quercetin that can stay in solution. The solubility effect appears to be colloidal. Flavonols are stacked together with other more
soluble compounds forming a soluble micelle. As a result flavonol aglycones are more soluble in wines with high levels of anthocyanins and tannin. This can be demonstrated in a model wine with excess quercetin. With no anthocyanins the model wine will support only about 2 mg/L of quercetin in solution. Adding anthocyanins increases quercetin solubility proportional to the amount of anthocyanin added. Adding tannin has a similar effect.
SG
Grenache
Merlot
CH
Tannin
315
308
462
15.8
Total Anthocyanins
71
57
359
<1
Quercetin Glycosides
105
38
94
7.9
Quercetin
20
17
38
7.2
Quercetin in Solution (mg/ L)
20
15
10
5
0
Precipitation Flavonol aglycones may exceed the capacity of a wine to keep them in solution either from increases in flavonol concentrations or from loss of co-factors. The insoluble flavonols will crystalize, initially forming needle-like crystals, as seen in the photo below. These can elongate to form hair-like structures that coalesce into mats.
0
200
400
600
800
Malvin Added (mg/ L)
Prior to bottling, quercetin precipitation is not usually a serious problem. The precipitate would not normally be noticed during winemaking operations. Occasionally yellow quercetin precipitates may be seen on bungs or filtration media. Quercetin precipitates occasionally cause filtration problems in both red and white wines.
Quercetin precipitates can form greenish clumps, often described as "slime", in the bottle and have resulted in expensive wine recalls, re-bottlings, and product losses.
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Bottle Precipitates A newly bottled wine is usually at a point of flavonol stability. Any precipitates that formed pre-bottling would have settled out in tank or barrel or have been removed by filtration. Any aglycones in the wine would be held in solution by phenolic co-factors. Bottle precipitates take time to form and they have two separate but related causes. Red wines in bottle contain a residual pool of flavonol glycosides. These compounds continue to slowly hydrolyze in the bottle adding to the pool of flavonol aglycones. Concurrently, anthocyanins are also hydrolyzing in a
similar reaction. Anthocyanins like flavonols are glycosides, however, when an anthocyanin loses its sugar the resulting aglycones is unstable and rapidly degrades in wine. Other chemical processes may also be involved in anthocyanin degradation in wine. Anthocyanin losses in bottled wine are typically 50% per year. During bottle aging, the concentration of flavonol aglycones in the wine increases and one of its most important co-factors decreases.These processes happen in all red wines but only a few red wines form flavonol precipitates. Problem wines generally have high concentrations of flavonol glycosides, high levels of flavonol aglycones and low concentrations of anthocyanins and tannin. Flavonol bottle precipitates are particularly nasty. They
14 | WINEMAKERâ&#x20AC;&#x2122;S QUARTERLY
do not usually form a haze. The flavonol crystals form aggregates and eventually large clumps that pour into a glass with a plop. The clumps appear yellowish or greenish and do not look like something you should put in your mouth. They look like a foreign substance in the wine. Adding to the problem is the timing. It takes anywhere from six months to four years for the precipitates to form post-bottling so the problem happens in the market, not the winery, and often in the hands of the final consumer.
Quercetin
Flavonol Aglycones Isolated from a Wine Precipitate Kaempferol
Myricetin
ISO-Rhamnetin
Varietal Susceptibility Most red wines never form a flavonol precipitate. However Sangiovese does with disturbing frequency. Sangiovese naturally synthesizes high concentrations of quercetin glycosides in response to berry sun exposure. It is also low in both anthocyanins and tannin. It is genetically set up for potential problems. Grenache does not synthesize as much
quercetin glycosides as Sangiovese but it is even lower in anthocyanins and tannin. Other red varieties only have quercetin problems under unusual circumstances. Extreme early leaf removal has resulted in problems in Merlot and Pinot Noir.
Environmental Interactions ETS has seen an increase in quercetin precipitates from recent warm vintages. Quercetin synthesis is not affected by heat but grape anthocyanins levels are generally lower in warmer vintages and wine tannin may be as well. The lack of solubility co-factors may be more important than flavonol concentrations in these instances. UV light is
directly associated with flavonol synthesis and that may have implication for regional differences in the occurrence of flavonol precipitates. New Zealand has higher UV levels than California and we have seen flavonol precipitates in a range of varietals from New Zealand.
Prevention Avoiding flavonol precipitation starts in the vineyard but is most effective at the winery level. Although flavonol glycosides can be reduced by reducing sun exposure on clusters, high flavonol grapes are often high quality grapes. Sun exposure, loose clusters and small berries are hallmarks of a good vineyard. Extreme, early season leaf removal should be avoided in Sangiovese and Grenache as it will both increase flavonols and decrease anthocyanins. Blending with high tannin wine and PVPP fining have been the most effective strategies for avoiding precipitation problems. Sangiovese producers who have experienced a
bottle precipitation often do both. High tannin wines such as Cabernet Sauvignon, Petit Syrah, and Syrah have all been used as blending components. PVPP is not often used as a fining agent in red wine but it is particularly effective at removing quercetin from wine. Bench trials are a must as is testing the fined wines for quercetin. Several winemakers have noted that low fining rates of PVPP have improved the mouthfeel of a wine. This may be directly related to quercetin removal as quercetin has been noted to contribute a harsh character to wine. 25
White Wine
20 Quercetin (mg/L )
Flavonol precipitates are occasionally seen in white wines. Generally the problem is associated with mechanically harvested grapes. Skin contact during transport or excessive leafy MOG (leaves have quercetin glycosides also) can both contribute enough quercetin glycosides to a juice to cause problems later. White wines have no co-factors to support quercetin so precipitates can form at quercetin levels much lower than seen in red wines. Recent interest in orange wines, white wines with prolonged skin contact, could result in some potential problems in the future, but so far we have not seed a quercetin precipitate in an orange wine.
15 10 5 0
0
1
2
3
4
PVPP (lbs/ 1000 gal)
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