In a previous post, we discussed ways in which nutrient management during primary fermentation can affect hydrogen sulfide formation and the overall “health” of the wine. This week, we’re going to explore how to mediate hydrogen sulfide aromas and flavors in a finished wine.
Sulfur-Containing Off Aromas
In general, many wine sensory scientists and wine experts will agree that is relatively a bad habit to use the term “sulfur” to describe off-odors associated with hydrogen sulfide or “stinky” aromas that are usually described by the term “reduced.” One of the main arguments for avoiding “sulfur” as a description term for an aroma is due to the fact that there are actually several forms of aromatic sulfur-containing compounds found in wine, and they can have very different aromas (smells, odors) associated with that one compound. The most common groups of aromatic sulfur-containing compounds in wine are:
Sulfur dioxide (SO2)
Hydrogen sulfide (H2S)
Mercaptans or Thiols
Additionally, many sensory experts will advise further to avoid using the chemical names as descriptors for describing an aroma found in wine (e.g., using the term “hydrogen sulfide” to describe the hard-boiled or rotten egg aroma). It is typically recommended to use an actual descriptor when describing an aroma (e.g., using the term “rotten eggs” when that smell exists in wine).
Sulfur Dioxide (SO2)
Sulfur dioxide is an antioxidant and antimicrobial preservative frequently used in wine production. However, it is also produced by yeast during primary fermentation, which is why wines (and other fermented products) cannot be sulfur dioxide-free (commonly referred to as “sulfite free” in the mass media). The aromatic descriptor commonly associated with a high concentration of sulfur dioxide is termed “burned match,” but a high concentration of sulfur dioxide can also cause a nasal irritation that many will describe as nasal burning.
Hydrogen Sulfide (H2S)
Hydrogen sulfide is an aromatic compound that is commonly described as having a “rotten egg” or “hard-boiled egg” aroma. Like many sulfur-containing compounds, hydrogen sulfide has a low sensory threshold (<1 – 1 part per billion, ppb), indicating that about 50% of the population could sense this compound at that concentration without being able to identify it, specifically, as hydrogen sulfide.
As we saw in our previous post, hydrogen sulfide development can result as a component of poor nutrient management during primary fermentation. Residual elemental sulfur from pesticide sprays has also been linked to latent development of hydrogen sulfide in wines. In a 2016 edition of Appellation Cornell, Dr. Gavin Saks’ lab provided a detailed and practical report on how hydrogen sulfide can be a problem for winemakers post-bottling and the potential links to hydrogen sulfide development as a function of residual sulfur from the vineyard (Jastrzembski and Saks, 2016).
Occasionally, winemakers may also experience hydrogen sulfide formation during a sur lie aging period; a time in which the finished wine remains on the lees when lees are stirred in the wine. It is also common for sparkling wines, produced in the traditional method, to exhibit a small perception of hydrogen sulfide when the bottle is first opened.
Mercaptans/Thiols and Disulfides
Finally, mercaptans or thiols, sulfur-containing compounds that contain the functional group –SH, and disulfides, sulfur-containing compounds that contain a S-S bond, can also be problematic for winemakers when found at high concentrations.
The presence of sulfur-containing volatile compounds is not always considered detrimental to wine quality. For some wine grape varieties (e.g., Sauvignon Blanc), these classes of compounds can make up their varietal aroma. In very small concentrations, sulfur-containing compounds can also be aroma enhancers, indicating that their presence can actually make the wine smell fruitier than if they were not present in the wine. However, when at substantial concentrations, volatile sulfur-containing compounds can also produce various “stink” aromas that mask a wine’s fruitiness, freshness, and make the wine generally unappealing. This is phenomena is dependent on the concentration of the sulfur-containing compound and the chemical makeup of the solution (i.e., wine) it is in.
Mercaptans or thiols and disulfides have a variety of descriptors associated with them, and their perception is largely based on concentration. When we’re discussing the negatively-associated descriptors, common terms include: garlic, onion, canned asparagus, canned corn, cooked cabbage, putrefaction, burnt rubber, natural gas, and molasses amongst others.
Are There Sulfur-Containing Off-Aromas in Your Wine?
To identify if hydrogen sulfide, mercaptans/thiols, or disulfide-based off-odors exist in your wine, it may be best to use a copper screen as a bench trial. While analytical identification of these compounds is possible, it is often expensive and leaves the winemaker guessing on what to do next.
For a quick assessment of a wine’s aroma, winemakers can drop 1-2 pre-1985 copper pennies into a glass of wine to see if the aroma freshens. The freshening aroma is due to the fact that the copper from the penny is reacting with the sulfur-containing compounds in the wine and making them aromatically inactive.
The “penny test” is often used to quickly determine if a wine is suffering from reduction, the presence of several types sulfur-containing off-odors. Photo by: Denise M. Gardner
A technical copper screen takes a bit more work and should be conducted in a quiet and aromatically-neutral environment. It is recommended to do this outside of the cellar.
Copper addition, in the form of copper sulfate, is often used to remediate aromas/flavors associated with hydrogen sulfide. One-percent and 10% copper sulfate solutions can be purchased through your local wine supplier. The basic protocol associated with a copper screen is as follows:
Add 50 milliliters of wine to two glasses.
Label one glass “control” and the other “copper addition” (see image below).
Add 1 mL of 1% copper sulfate to the “copper addition” glass.
Cap both glasses for 15 minutes. Sniff the aroma of each wine.
Setting up a copper screen can help determine if a wine is suffering from aromas caused by sulfur-containing compounds. Photo by: Denise M. Gardner
Sniff (smell only!) both glasses. Most people start with the “control” and smell the treated wine (wine containing copper sulfate) second. If the aroma/flavor of the “copper addition” glass has improved, or the hydrogen sulfide aroma has subsided, then a copper addition trial should follow to determine the exact concentration of hydrogen sulfide needed to clean up the wine in question. Remember that the legal limit for copper allowed in a finished wine is 0.5 ppm.
Treatment of Sulfur-Containing Compound Off-Aromas
Sulfur-containing compounds are quite reactive, which can make dealing with them fairly difficult. Many educators agree that the best way to treat sulfur-containing compounds, especially those that stink, is to prevent their existence as best as possible.
In the Appellation Cornell newsletter that focused on sulfur pesticide residues, Jastrzembski and Saks (2016) recommended that sulfur residue concentrations should not exceed 1 mg/kg at harvest in order to avoid latent hydrogen sulfide or sulfur-containing off-aromas later in processing and storage. Additionally, many experts recommend appropriately treating fermenting musts with nutrient management strategies based on the starting YAN concentration to minimize the incidence of hydrogen sulfide formation during primary fermentation.
As described above, winemakers may also opt to treat the wine with copper sulfate to try to reduce the perception of hydrogen sulfide or other sulfur-containing aromas. It should be noted that aromas caused by disulfides cannot be mediated with a copper sulfate addition.
There has been more conversation in the academic community regarding the reemergence of hydrogen sulfide or sulfur-containing off-aromas after a wine has been treated with copper and post-bottling. The theory around this appears to circulate around residual copper initiating reactions in the wine that lead to more sulfur-containing off-odors. This continues to be an ongoing discussion amongst researchers and will likely be a hot topic within with the wine industry. For now, it is important for winemakers to understand that there may be a risk of off-odors reemerging post-copper treatment and post-bottling. This topic will also be discussed to some degree at the 2017 PA Wine Marketing and Research Board Symposium on March 29, 2017 in State College, PA, and winemakers are encouraged to attend.
Some hydrogen sulfide or sulfur-containing off-odors can sometimes be mediated with use of fresh lees stirred in the wine or the addition yeast lees-like products. Winemaking products like Lallemand’s Reduless, yeast hulls, or some cellulose-based products can help reduce or eliminate the intensity of these off-odors. As with any other product additions, it is recommended that wineries always do bench trials first and before adding to the entire volume of wine. Additionally, Enartis USA (Vinquiry) has previously distributed a fact sheet to help winemakers troubleshoot reduced wines and determine how to best treat a problem wine.
The incidence of reduction, sulfur-containing off-odors, or hydrogen sulfide can be a frustrating circumstance for winemakers. However, adequate vineyard care and proper nutrient management during primary fermentation can help minimize the incidence rate of sulfur-containing off-odors from occurring in their wines. Of course, problems with wines do occur, and we hope that the recommendations above will help winemakers solve wine problems pertaining to sulfur-containing off-odors.
Yeast assimilible nitrogen (YAN) is the sum of the amino acid and ammonium concentrations available in the grape juice at the start of fermentation. Typically, the amino acid proline is not included in the reported amino acid content as it is not readily utilizable by yeast cells.
The amino acid component of YAN is often referred to as the “organic” YAN form. In contrast, the ammonium ion content is referred to as the “inorganic” YAN form and may be written in its ionic abbreviation: NH4+. Due to the fact that ammonium is only connected to a series of protons (H+ions), it tends to be easier to move in and throughout the yeast cell to be consumed during fermentation (Mansfield, 2014). When these two components (organic + inorganic) are added together, the resultant value is the YAN, written with the units: mg N/L.
The winemaking challenge associated with YAN is the fact that it is quite variable, and current research has not identified ways to change the YAN, predictively, in fruit through the manipulation of vineyard practices. YAN varies by vintage year, grape variety, cultivar, and with the use of various vineyard management practices. In Penn State’s research vineyards, ~1 acre in size and containing 20 different wine grape varieties, YAN values ranged dramatically each vintage year amongst the various wine grape varieties. On any given vintage year YAN values ranged from low (<100 mg N/L) to high (>300 mg N/L) amongst the varieties grown in that one site.
The variability associated with YAN provides a secondary challenge to winemakers: the lack of predictability associated with hydrogen sulfide formation during primary fermentation due to unfulfilled nitrogen needs by wine yeasts.
What does YAN have to do with Hydrogen Sulfide?
Winemakers often talk about YAN in relation to hydrogen sulfide (H2S) as the two have been associated with one another throughout primary fermentation. Although there are several potential causes of hydrogen sulfide formation during wine production, some of which we will talk about in our Part 2 series, nitrogen imbalance has been one of the factors that winemakers can influence through production. Unfortunately, there is no way to ensure that a wine will not produce hydrogen sulfide by the end of fermentation, but treating wines with proper nutrient supplementation can help minimize the incidence of hydrogen sulfide production during primary fermentation.
Hydrogen sulfide is produced by the yeast cell via the sulfate reduction pathway (Figure 1). While I know this figure looks scientifically daunting, we can try to simplify its purpose to discuss how hydrogen sulfide is released into wine. Sulfate (SO42-), naturally abundant in grape juice (Eschenbruch 1974), is transported into the yeast cell for amino acid (cysteine and methionine) development, which are naturally lacking in concentration in grape juice (Bell and Henschke, 2005). Energy is used by the yeast (represented as ATP in Figure 1) to chemically alter the structure of sulfate in order to make it useable by the yeast cell. This useable form can be seen as sulfide (S2-) in the image below. Using nitrogen, which is required to make an amino acid, the sulfide content is depleted as cysteine and methionine amino acids get produced. Therefore, as sulfide reserves are depleted, cysteine and methionine contents generally increase to be used for building proteins that will be needed by the existing or new yeast cells.
Figure 1: A simplified version of the sulfate reduction pathway.
Sulfur dioxide (SO2) plays a role in the sulfate reduction pathway in that it bypasses the transport mechanism required to bring sulfur into the yeast cell. It other words, it can diffuse across the cell membrane and into the internal parts of the yeast cell. Sulfur dioxide will get chemically altered to be made into the useable sulfide , S2-, form as well. Therefore, fermentations that contain a high concentration of sulfur dioxide at the start of fermentation have the potential to increase the utilization of sulfur dioxide during yeast metabolism.
These processes function normally until a depletion of nitrogen (from the nitrogen pool) or an accumulation of sulfide develops in the yeast cell.
If there is not enough nitrogen (low YAN fermentations) available to make the sulfur-containing amino acids (cysteine and methionine) then, eventually, the yeast cell will not be able to continue manufacturing these amino acids. In this situation, the sulfide concentration generally starts to increase within the yeast cell.
The chemical form sulfide, however, is toxic to the yeast cell and thus, the yeast will try to eliminate it from its internal structures. Therefore, when sulfide concentrations get too high, the yeast will diffuse this across its cell membrane into the surrounding media: the fermenting juice. When hydrogen sulfide concentrations get high enough in the fermenting juice, winemakers can often sense the rotten or hardboiled egg aroma associated with the compound.
What if there is too much nitrogen?
In contrast, too much nitrogen (high YAN fermentations) can also be problematic. Higher concentrations of the inorganic component of YAN can lead to a high initial biomass (population) of yeast. The rapid increase in yeast populations can lead to nutrient starvation by a majority of the yeast when the wine is about almost finished completing fermentation. With a large biomass of yeast incapable of obtaining the proper nutrient (nitrogen) content to grow and reproduce, hydrogen sulfide development can result. This is due to the fact that there is a large population of yeast in situations in which there is not enough nitrogen to support their growth (i.e., there is not a lot of food to go around for all of the yeast cells). With hydrogen sulfide development occurring late in primary fermentation, it is obvious that the winemaker would become concerned with hydrogen sulfide retention by the time fermentation is fully complete.
Too much nitrogen can also cause other quality problems. Due to the excess amount of available nutrients, yeast can grow and reproduce quickly, which often leads to very rapid or very hot fermentations. The speed of fermentation, of course, can affect the aromatics and quality of the wine (i.e., fast fermentations often lead to simpler aroma and flavor profiles). This may not be an issue with some styles of wine, but for many white wine or fruit (other than grapes)-based fermentations, aromatic retention is often a priority by the winemaker.
Due to the fact the initial YAN is so high, all of the nitrogen contents may not be utilized by the yeast population by the end of fermentation, and could remain in suspension in the finished wine. As yeasts begin to autolyze, all of their inner components, including the remaining nitrogen content, will become available in the wine. The excess “food” could be available for other microorganisms (like acetic acid bacteria, lactic acid bacteria, or Brettanomyces), which could potentially lead to spoilage problems if the wine is not properly stabilized. Such spoilage is, obviously, detrimental to wine quality and undesirable by the winemaker. Alternatively, remaining nutrients could be utilized by malolactic bacteria or those wines that will be given tirage for sparkling production (Bell and Henschke, 2005).
Finally, higher YAN concentrations can lead to an increased risk of ethyl carbamate production in wine; ethyl carbamate is a known carcinogen that can give susceptible individuals headaches, or even respiratory illness. Ethyl carbamate is produced in a reaction between ethanol and urea (Bell and Henschke, 2005). The heavy use of DAP has also been linked to a higher potential risks of ethyl carbamate due to the fact that DAP inhibits the transport of amino acids into the yeast cells, and therefore, leaves a higher concentration of amino acids available that can potentially be altered into urea, a precursor for ethyl carbamate (Bell and Henschke, 2005).
The fact that excess nitrogen can be problematic during wine production should provide insight to winemakers to avoid over-supplementing their fermentations. Hence, it is often recommended to that winemakers measure and identify their starting concentration of YAN and supplement accordingly.
Nitrogen (nutrient) management and supplementation is not uncommon during primary fermentation as nutrients are an important component of yeast cell growth and metabolism. In the yeast cell, nitrogen is a required nutrient in the synthesis of amino acids and to build proteins that are used in the yeast cell walls and organelles, as discussed above. Without protein development, the yeast cell cannot live.
Winemakers can supplement their fermentations with nitrogen by adding nutrient supplements in the form of:
Hydration nutrients (e.g., GoFerm, Nutriferm)
Complex nutrients (e.g., Fermaid K, Nutriferm)
Diammonium phosphate (DAP)
DAP is considered an inorganic form of nitrogen, while the complex nutrients may contain additional organic yeast components that contribute organic forms of nitrogen. Recall, above, that the inorganic form of nitrogen is more readily consumed by yeast, and it can be easily absorbed by yeast cells even as alcohol concentrations rise during primary fermentation. Amino acids, on the other hand, require energy expenditure in order to be brought into the cell through transport proteins located on the cell membrane. The presence of both alcohol and ammonium ions inhibit the transfer of amino acids from the juice into the yeast cell (Santos, 2014). Therefore, it is often recommended to avoid the addition DAP or products that contain DAP (i.e., Fermaid K, Nutriferm Advance) at inoculation and until after yeasts have the opportunity to best absorb amino acids.
Starting YAN Concentrations
Nonetheless, nutrient supplementation strategies are often based on starting YAN concentrations in the fruit. Due to the regular variability of YAN concentrations, winemakers are encouraged to measure YAN for each lot of grapes every year. This is often problematic for winemakers whom do not have the time to run the appropriate analyses associated with YAN or the financial resources to send samples to an analytical lab. Such challenges force many winemakers into a situation in which all fermentation lots are treated with the same repeated nutrient supplementation regardless of the starting concentration of YAN.
In previous Extension workshops, research from Cornell University on Riesling wine grapes found that they could accurately predict the harvest YAN when good field samples were taken within 2 weeks from harvest (Nisbet et al., 2013). In 2016, Cornell released a second publication that focused on YAN prediction models for Cabernet Franc, Chardonnay, Merlot, Noiret, Pinot Noir, Riesling, and Traminette. While the prediction models were not recommended for regions outside of the Finger Lakes (where the data was sourced from for this study), they found that in some cases, YAN data could be obtained within 5 weeks of harvest (Nisbet et al., 2014). This extra flexibility in time can aid in obtaining accurate YAN results before the grapes reach the crush pad, which ultimately helps winemakers prepare for nutrient supplementation before the start of fermentation.
Until further research can provide predictive modeling for other wine regions, it is generally accepted that winemakers should measure YAN at or as close to harvest as possible.
YAN can be measured using the following the analytical procedures:
Enzymatic methods for both primary amino acids and ammonium.
While the Formol titration is often preferred by many small wineries due to the lower start-up investment, the use of formaldehyde, a known carcinogen and lung irritant, in this protocol does require some consideration for laboratory safety. Additionally, the proper disposal of formaldehyde, a hazardous substance, can be an issue for many wineries.
Enzymatic methods by spectrophotometer definitely require a bit of experience in order to become more efficient in their use, which can be problematic for those operations that find measuring YAN too timely. Additionally, enzymatic kits have to be purchased fresh and have a small shelf life. The advantage of investing in a spectrophotometer, however, is that other enzymatic kits can be purchased to measure additional wine components including residual sugar, malic acid, and acetic acid.
Nonetheless, measuring YAN should be a consideration for wineries that struggle with hydrogen sulfide aromas by the end of primary fermentation. It is through the starting numerical value that winemakers can better manage and adjust nutrient supplementation strategies to help minimize the reoccurrence of hydrogen sulfide at the end of fermentation.
Nutrient availability during primary fermentation is only one potential contributor to hydrogen sulfide formation in wines. In the next blog post, we’ll explore other potential causes of hydrogen sulfide formation and how to best mediate the problem when it exists.
Eschenbruch. R. 1974. Sulfite and sulfide formation during winemaking – a review. Am. J. Enol. Vitic. 25(3): 157-161.
Bell, S.-J. and P.A. Henschke. 2005. Implications of nitrogen nutrition for grapes, fermentation and wine. Aust. J. Grape and Wine Res. 11:242-295.
Mansfield, A.K. Are you feeding your yeast?: The importance of YAN in healthy fermentation. Webinar. Feb. 2014.
Nisbet, M.A., T.E. Martinson, and A.K. Mansfield. 2013. Preharvest prediction of yeast assimilable nitrogen in Finger Lakes Riesling using linear and multivariate modeling. Am. J. Enol. Vitic. 64(4): 485-494.
Nisbet, M.A., T.E. Martinson, and A.K. Mansfield. 2014. Accumulation and prediction of yeast assimilible nitrogen in New York winegrape cultivars. Am. J. Enol. Vitic. 65(3): 325-332.
Santos, J. Getting Ready for Harvest: Yeast Nutritional Needs. Workshop Seminar. July 2014.
Gut reaction: Viruses cause disease. Disease is bad. Viruses are bad.
Gut reaction muted by a lot of recent genetics research: Viral DNA seems to be embedded in genomes all over the place. We’re not sure why a lot of it is there, or stayed there, or what it does while its there. Some viruses cause disease. Some don’t. Viruses are complex, and we probably don’t know the half of it yet.
A name like “grapevine leafroll-associated virus” gets you thinking about negative consequences. Rolled leaves don’t collect light efficiently, which means that they won’t contribute to the plant’s photosynthetic metabolism efficiently, which means that the plant may be malnourished, grow slowly, and/or not have enough energy to ripen fruit. Rolled leaves are bad. A virus that’s associated with rolled leaves is bad. But the virus is only associated, not causative. Some viruses in this general family of leafroll-associatedness aren’t associated with vine symptoms. And infected vines only show symptoms post-veraison (the stage of ripening at which grapes change color), even though they carry the virus in detectable quantities year-round.
Ergo, a group of vine and wine scientists headquartered in eastern Washington state designed an experiment to ask (published in PLOSOne, and therefore open-access to everyone): do grapes from vines with grapevine leafroll disease, and carrying one of these viruses (GLRaV-3), lag behind their undiseased counterparts throughout ripening, or only when vines show symptoms? Being particularly conscientious*, they also improved on existing studies of grapevine leafroll disease by collecting data for three consecutive years from a commercial vineyard, sampling grapes throughout the season but also harvesting grapes at the typical time and making wine from diseased and undiseased pairs, and subjecting those wines to (limited) chemical and sensory analysis. They also used own-rooted rather than grafted vines, which eliminates some potentially confounding variables.
By: Denise M. Gardner, Enology Extension Associate
Most likely, all of the wines from the 2016 vintage are happily settling away in tank or barrel at this point. After such a busy time, his leaves winemakers with that tricky question, “What do I do now?”
Monitoring Malolactic Fermentation (MLF)
Now is a good time to make sure you are monitoring your malolactic fermentations. Ensure all of your barrels or tanks have been appropriately inoculated, or have started naturally, and get some initial readings on the malic acid concentration.
If you have a spectrophotometer, you can purchase enzymatic kits to measure the concentration of malic acid in your wine over time. Wines with less than 30 mg/100 mL of malic acid are considered “dry” for MLF or MLF-stable for bottling.
However, winemakers can also monitor malic acid degradation through the use of paper chromatography kits. These kits are easy enough for home winemakers to use and can also be applied at the commercial level.
MLF paper chromatogram. This image shows the paper after it has dried, where the spots are pertaining to the acid standards and the acid separation for a wine sample. Wine samples above have not completed MLF due to the fact there is a noticeable dot of malic acid in each sample. Photo by: Denise M. Gardner
Paper chromatography works by separating tartaric, malic, and lactic acids from a wine sample (Figure 1). In addition to blotting small drops of your various wine samples, each paper must also contain 3 standards to show the spots documented by the three acids (tartaric, malic, and lactic). While paper chromatography is not the best at concentrating how much of each acid remains in the wine, you can get an idea when the bulk of malic acid is converted to lactic acid (i.e., MLF is completed) when the malic acid spot associated with the wine samples disappears.
Checking Wines for Off-Flavor Development
It’s also a good time to check wines for hydrogen sulfide (H2S) or sulfur-base off-odor aromas, and volatile acidity (VA), especially for wines that you will want to bottle early in the new year.
Now is also a good time to know what the VA is in your wines, especially those that will be seeing some aging. This is incredibly important to get a baseline value of the VA. That way, if a problem emerges in the future, you will have an indication how much the volatile acidity has increased. Penn State Extension also offers a 2-page fact sheet explaining why knowing volatile acidity is important, provides protocols for its analysis, and how to mediate high VA situations: http://extension.psu.edu/food/enology/wine-production/wine-made-easy-fact-sheets/volatile-acidity-in-wine
If you are having problems identifying these key defects in your wine, don’t forget that the annual “Wine Quality Improvement” Short Course is just around the corner in January.
Now is also a good time to clean up any leftover sore spots from the chaotic harvest season:
Clean up places in the cellar that have gotten dirty or have become areas that are accumulating materials that should otherwise be put away.
Manage all of your harvest records. Make sure all of the wines have the basic wine chemistries (e.g., pH, TA, residual sugar, alcohol, free and total SO2, malic acid, and volatile acidity) in the record book. It is easy to forget all of these details as time progresses.
Running basic chemical analysis on your wines and updating records is an essential component of making quality wine. Photo by: Denise M. Gardner
The conversion of malic acid to the weaker lactic acid during malolactic fermentation (MLF) is not the only important change that occurs during this process. Other intermediate and co-products are also formed, which will have a secondary influence on the wine composition. The decrease in the colour is one such product, but the reason for it is unknown.
Wine quality and its sensory description are determined by factors like flavour, taste and mouthfeel, but especially in the case of red wines the colour is also an important factor. This is especially applicable in the case of light coloured red wines like Pinot noir. Much research was consequently done to determine which viticultural and cellar practices will optimise the colour. The colour of red wines is not only determined by the anthocyanin concentration of the wine. After being extracted from the skins, the anthocyanins can react with different compounds in the wine to form more complex colour compounds. They may for example react with tannins to form polymeric pigments. This formation can be accelerated by reactions with acetaldehyde. Stable anthocyanin derivative products can also be formed by reactions with pyruvic acid. All these pigments are more resistant to oxidation and bleaching by sulphur dioxide (SO2), and also tend to increase during wine maturation.
It is known that winemaking factors like fermentation temperature and extended maceration influence the formation of polymeric pigments. Yeast can also influence the colour of red wines by the adsorption of anthocyanins to their cell walls or by the formation of acetaldehyde and pyruvic acid. Yeast strains differ regarding the acetaldehyde concentration which is formed and will consequently have different effects on the colour of red wines. Other micro-organisms can also influence the colour of red wines. It is for example known that Oenococcus oeni decomposes acetaldehyde and pyruvic acid during MLF …
While in the midst of harvest (and all the craziness that comes with it), I thought I’d take a week to remind people about proper cleaning techniques, improving sanitation, and why these two operations are essential for wineries.
I know many of you are ready to close this page now, but WAIT!
I have heard many excuses for short cutting on cleaning over the years. Do any of the following sound familiar?
There is not enough time in the day to properly sanitize.
There are not enough employees to do all the work to properly clean.
Cleaning would take all night to complete properly.
It’s not necessary to clean/sanitize with wine.
The wine will sell anyway.
Cleaning and sanitizing does not actually improve wine quality.
Sanitation is not really important.
Proper cleaning does not increase the price in which the wine can be sold.
If you or any of your employees have used at least one of these statements in the past, you could be suffering from poor cleaning and sanitation practices!
In all seriousness, having good cleaning and sanitation procedures can actually save the winery time and money in the long run.
In the height of harvest, I’m sure this is a tough sell. But let’s consider some of these practical cleaning and sanitation suggestions for small, commercial wineries.
On the same page with cleaning vs. sanitizing
Let’s start with a review of definitions, as it can get very confusing. Below are some general definitions taken from a series of sources (Fugelsang and Edwards 2007, Iland et al. 2007, Iland et al. 2012, Solis et al. 2013) to explain the differences between cleaning, sanitation, and sterilization.
Cleaning – the physical removal of dirt, debris or unwanted material (solid or liquid) from a surface
Sanitizing – a 99.9% (3 log) reduction of microorganisms
Sterilizing – the complete removal or inactivation of microorganisms
The wine industry is primarily focused on cleaning and sanitation protocols, as there are not many sterile practices utilized in winery operations (unless you are one of the lucky few wineries bottling aseptically). Even if processors are using sterile filtration to remove yeast and bacteria from the wine, once the wine exits the filter, it comes in contact with equipment that is only sanitized (hopefully!).
Additionally, wine bottles or packages are not sterile when being filled. Even new bottles can contain yeast or bacteria that can potentially contaminate a finished wine. Hopefully, proper sulfur dioxide levels should keep this microorganisms at bay.
For all of these reasons, as the wine has the opportunity to come in contact with existing microflora on processing equipment, wine is bottled in a sanitized environment.
Remember proper sanitation is primarily having good cleaning protocols. Cleaning should always precede sanitation. Failure to physically remove all of the debris from equipment, results in an inability to properly conduct sanitation procedures.
There are several different detergents (cleaners) and sanitizers that wineries can use effectively. Example sanitizers include quarternary ammonium compounds (QUATS), peroxyacetic acid, chlorine dioxide, hot water, and steam. Additionally, wineries can find use in an acidulated (citric acid) sulfur dioxide mixture. However, all sanitizers should be selected specifically for the job at hand (Iland et al., 2012) with consideration towards the microbes that one is trying to avoid.
Most commercial wineries can really focus on improving cleaning practices to provide a step in the right direction towards improving quality and sanitation practices inside the winery.
While this is usually one of the places winemakers feel most complacent about, I would argue that this can be one of the most important places to take care in your cleaning and sanitation practices.
There is a lot of effort that goes into the growing season in order to adequately ripen wine grapes for many sensory nuances. Additionally, the vineyard is the source of many microorganisms that enter the crush pad and cellar. [For those that use mechanical harvesters, do not forget cleaning and sanitation of this vital piece of equipment (Pregler 2011).] Giving the grapes a clean surface to encounter upon entering the winery ensures that all of that hard work is truly appreciated and preserved from the start of fermentation.
Without proper cleaning and sanitation practices, you are likely increasing the microbial populations of your wine before it even gets a chance to ferment. Think about it. After crushing/destemming a lot of rotting Pinot Grigio, Pinot Noir, or botrysized Riesling, how many people spray down the equipment (lightly) and move onto crushing the next lot of fruit even if the second lot is cleaner than the first? Sometimes, the order of grape crushing cannot be avoided. But how it is handled upon receiving can be altered. If this is the case for your winery, and you are avoiding good cleaning and sanitation steps in between lots of fruit, you are cross contaminating your juice with, not only yeast and bacteria present in the rotted fruit, but also residual enzymes, proteins, and other by products that can alter wine chemistry in the clean fruit that follows. Think about the potential production problems this can cause later on down the road: laccase browning, acetic acid development, off-flavor development, etc. If such problems arise, it can cause labor and financial investment at a later time.
Residual foodstuffs (e.g., old grape skins, rice hulls, pulp) can contribute to off flavors within the finished wine. Recent research has shown that there is potential for aromatically-intense varieties (i.e., Niagara, Concord, or Noiret) to leach their flavor compounds into more neutral varieties through absorption and diffusion of equipment-based plastic components that come in contact with the juice and wine (Smith 2014). It is also possible for alien material (i.e., green matter, old rice hulls, and stuck fruit) to contribute to flavors in the final product that may be undesirable or challenging to fix.
Remember that rice hulls are a pressing aid primarily used for A) hard-to-press varieties to increase yield or B) bulk operations in which pressing time is of the essence. Previous studies, such as the one found here, have shown a detriment in flavor and quality of wines pressed with rice hulls for certain varieties. Additionally, rice hulls can be difficult to remove from the wine press and create potential microbial infection sites for later grapes/juice/wine. It is recommended that the use of rice hulls be on aromatically intense or difficult-to-press varieties (e.g., many native varieties). Use of rice hulls in grapes that have a lot of rot will not only help increase yield of the fruit, but also increase extraction and retention of rot byproducts, which can contribute to off-flavor development.
Proper cleaning can help maintain your equipment longer. Over time, plant material can slowly degrade equipment. Doing a little scrubbing and properly sanitizing repeatedly can help keep your equipment in relatively good condition. Additionally, the longer debris is left on equipment, the harder it is to remove.
Figure 1: Preparing a small solution of acidulate sulfur dioxide to sanitize processing equipment before crushing/destemming and pressing operations. Photo by: Denise M. Gardner
Properly maintaining harvest equipment also leads a good example for all of the other equipment in the winery.
Tanks, Barrels and Bottles
These are places in the cellar where it can get easy to take short cuts as opposed to properly cleaning or sanitizing equipment.
These are places in the cellar where it can get easy to take short cuts as opposed to properly cleaning or sanitizing equipment.
Remember that tartrate build up in tanks and barrels can make it difficult to properly sanitize the covered portion of the tank/barrel. Make sure to first dissolve large tartrate deposits with hot water before going through a cleaning and sanitation cycle. Without dissolving tartrates, the equipment is not going to get properly cleaned or sanitized.
When getting ready to fill a tank, remember to run a sanitizer through the tankfirst to minimize microbial populations on the interior surfaces that come in contact with the wine. This helps ensure varietal flavor nuance and minimizes the risk for spoilage. [Note: Some sanitizers are no-rinse sanitizers and do not require a rinse after the sanitation chemical is applied. Other sanitizers may require a rinse following application. Always check the directions pertaining to your sanitizer carefully before use to ensure it is being used properly for best efficacy, and always use proper protective clothing when handling sanitizer agents.]
Minimize harboring sites for insects and microbes within the cellar are a practice that can be done at the end of every shift. During harvest, one big problem I see is dripping, dried juice or wine on the exterior of tanks or fermentation bins. While this doesn’t seem like a big deal, it’s an attractive site for fruit flies, which also makes them attractive deposits for spoilage yeast and bacteria. The objective of removing these places of dried juice/wine is to minimize insect infestation in the winery and avoid potential contamination of clean wines.
Barrels need cleaned prior to sanitation regimes like other pieces of equipment. Many barrel cleaning systems are automatic and can be an efficient way to clean the interior of barrels.
Barrels are porous and have a lot of grooves inside of them, which can make it difficult to properly clean and sanitize. It is important to note that due to the nature of the barrel, it cannot be sanitized in a way that a stainless steel tank can be sanitized. However, there are many different cleaning and sanitation options for barrels out there, some of which are explored in this Appellation Cornell newsletter from 2013. This study evaluated natural barrel microflora (yeast, including Zygosaccharomyces and Brettanomyces) before and after a sanitation regime was conducted.
Sulfur wicks are a good way to treat the interior surface of the barrel, but this practice does not penetrate into the interior of the wooden staves (Iland et al. 2007). Also, ensure that the wick is not submerged below any left over water at the bottom of the barrel, as it may extinguish the wick (Iland et al. 2007). Make sure the bung is tightly sealed for best efficacy of a sulfur wick (Rieger 2015).
Bottling lines are not immune to cleaning. In the food industry, it is commonly noted that most contamination comes from the environment in which the food is processed. This can happen in wine processing, as well. Dust on the bottling line can harbor yeast and bacteria that can be disturbed or moved into the air during large movements, like when bottling a finished wine. Keeping the bottling line clean is a good way to help minimize contamination during bottling operations.
Small Steps That a Commercial Winery Can Take to Improve Cleaning and Sanitation
Being a smaller or boutique sized winery can definitely have its advantages in the cleaning and sanitation world. It’s easy to get creative in terms of improving efficiency, use of, and efficacy of cleaning and sanitation practices. Below are some practical solutions for wineries struggling to incorporate cleaning and sanitation practices in the winery.
Use brushes, like Perfex brushes, to properly scrub equipment during cleaning operations. These are especially helpful when getting that pesky debris off of processing equipment.
Color code brushes or cleaning materials to emphasize their use and make it easier on your employees. By keeping the necessary supplies handy and easy to use, efficiency is likely to improve, which can actually help improve the quality of cleaning operations. Typically, white brushes are reserved for food-contact surfaces (the part of the equipment that actually comes in touch with food) during sanitation steps. Yellow brushes can be used for environmental cleaning (non-food-contact surfaces like the exterior of tanks). Other colors can be purchased for additional specific purposes: detergent only, sanitizer only, etc. Keep the brushes handy during all processing operations.
Figure 2: Perfex Brushes that are great for cleaning and minimize bacteria retention.
Consider keeping your cleaning and sanitation system on wheels. While in Oregon, I found it clever how larger wineries kept their fittings on mobile units to aid in availability, cleaning, and organization (Figure 3). While this concept may be helpful to some wineries, I think it can also be applied to cleaning materials. Keeping cleaning materials isolated to a mobile until allows for quick use and organization throughout the entire production facility and minimizes needless travel time to walk back and forth towards where supplies may be kept. Examples, below, for how to improve mobility of your cleaning supplies are given in Figure 4.
Figure 3: Mobile unit for holding cellar fittings is a great idea for easy organization, cleaning, storage, and use of fittings throughout a cellar. (Looking at mobile stand from the top) Photo by: Denise M. Gardner
Figure 4: Utility carts like this plastic one from School Outfitters or the metal one from Grainger can be easy additions to hold necessary cleaning supplies like citric acid/sulfur dioxide and pH strips, as well as hang spray bottles or hold gloves for cleaning. Carts can be easily moved and stored in the cellar for convenience.
You do not need to use fancy (or expensive!) cleaners or sanitizers all of the time in the winery. For quick clean ups, use warm water mixed with potassium carbonate to get stuck or sticky material off of equipment. Use with caution as it can get slippery!
Follow a potassium carbonate rinse with a warm water rinse to remove the solution from equipment and environmental surfaces.
Acidulated sulfur dioxide (Figure 5) can act as a quick sanitizer as well, and is easy to make up and use in the winery. Plus, citric acid, sulfur dioxide, and water are found in wine and will not have an effect on wine quality or flavor.
Figure 5: Keeping acidulated sulfur dioxide handy can be a quick sanitation solution during processing days. Photo by: Dr. Rob Crassweller
Finally, I always recommend wineries keep a supply of 70% ethanol in a spray bottle handy for quick cleaning solutions. Ethanol can be used to clean up small spills, quickly rinse sampling valves before and after sampling, or act as an exterior sanitizer towards things like wine thieves, sampling pipettes, and lab benches where one is running analysis. This is an easy chemical to keep on a mobile cart or scattered throughout the winery. However, be sure to purchase food grade ethanol from a chemical supplier and dilute down to ~70% with non-chlorinated water.
Cleaning up at the end of a processing day makes the start up for the next processing day a lot easier. If the equipment is clean to start, then all you have to do is run a quick sanitizer through the equipment before the start of processing operations.
Use hot water to rinse your equipment and make sure your hose has good pressure. Cold water is definitely energy efficient, however, hot water can help remove a lot of debris quicker and make any potential scrubbing easier. Be cautious of the metal on equipment heating up with use of hot water. Also, increasing hose pressure can help dislodge any debris from equipment, which can save time during cleaning operations.
On large processing days (those days when 3 or 4 varieties are being crushed at the winery), designate the day to processing and wait until the next day to complete other operations that can be delayed. Now, some flexibility needs to be made for things like punch downs or pump overs. However, teamwork is key: punch down time can be reduced if there is more than one punch down tool available for employees to use. Juice analysis (pH, TA, Brix, and YAN) is time sensitive, because if the juice starts going through spontaneous fermentation, the results of these chemical indices will change. However, obtaining all of the juice samples from all lots of incoming fruit before starting analysis can save your employees time and avoid splitting up duties during a processing day. With 3 employees, one person could run analyses while the remaining 2 finish cleaning up at the end of a processing day. Reserve racking or moving wines for days when a little less is going on in the cellar unless it is absolutely necessary to open up space in tanks for incoming fruit.
Minimize barrel-to-barrel or tank-to-tank contamination by having small sanitation vessels/buckets (filled with sanitizer) handy and isolated for cleaning/sanitation use. Use a bucket filled with acidulated sulfur dioxide solution to submerge (and fill) your wine thief in prior and after each barrel sample. For smaller samples, consider using one-time-use or disposable pipettes (Figure 6). If you have a 70% ethanol solution in a spray bottle, the metal fittings at the end of hoses can be quickly sprayed in between barrels when transferring barreled wine into a tank or transferring wine from a tank into barrels to help minimize cross contamination (Illand et al. 2007).
Figure 6: Serological or disposable pipettes are a great way to avoid cross contamination when smaller samples are needed. Photos from BioVentures.
Check to see how clean your equipment is with quick testing strips like Pro-Clean Protein Residual testing strip by Hygiena. These testing strips are a good indicator on how well your cellar crew is cleaning equipment. The problem with protein test strips, like the one shown, is that it will detect all organic matter (Iland et al., 2007). It does not represent live or viable microorganisms; there are rapid tests available that may be more representative of microorganism populations.
The video below indicates the ease in which these are to use:
Other options include luminometers like Hygiena’s SystemSURE Plus or 3M Clean-Trace (Rieger 2015), which are also non-specific, but can indicate the cleanliness of a contact surface that is swabbed properly.
While cleaning and sanitation may seem arduous, most wine quality problems I encounter – including funky off-flavors that are challenging to identify, presence of VA, large quantities of wine affected by cork taint, and lack of varietal character – could be primarily avoided with more routine and better cleaning operations. Improving cleaning and sanitation operations can be a step in the right direction for wineries to improve quality associated with their business.
Smith, JC. 2014. Investigating the Inadvertent Transfer of Vitis labrusca Associated Odors to Vitis vinifera Wines. Retrieved from Electronic Theses and Dissertations for Graduate School: Penn State: https://etda.libraries.psu.edu/catalog/23501.