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New World Wine Maker Blog - Technical Articles

Using MLF to create a buttery wine or not

by Natasha Pretorius, Lynn Engelbrecht & Maret du Toit – Wineland Media

Various factors influence the amount of diacetyl, acetoin and 2,3-butanediol produced during fermentation impacting the buttery aroma.

Malolactic fermentation (MLF) is a secondary fermentation carried out by lactic acid bacteria (LAB)This process can occur spontaneously or can be induced by using MLF starter cultures. Currently, the commercially available MLF starter cultures belong to the species Oenococcus oeni and Lactobacillus plantarum. The use of starter cultures to induce MLF is preferred to avoid the risks associated with spontaneous MLF. The starter cultures can be inoculated simultaneously with the yeast, known as co-inoculation, or after the completion of alcoholic fermentation, known as sequential inoculation. MLF is a desirable process as the decarboxylation of l-malic acid to l-lactic acid and carbon dioxide decreases the acidity and increases the microbial stability of wine. This process also influences the organoleptic properties of wine.

In addition to malic acid, some MLF starter cultures can also degrade citric acid usually present in grape must at concentrations of 0.031 g/ℓ to 0.42 g/ℓ. The metabolism of citric acid leads to the production of acetate, d-lactate, diacetyl, acetoin and 2,3-butanediol (Figure 1). The production of acetate is one of the reasons for the 0.1 g/ℓ to 0.3 g/ℓ volatile acidity increase during MLF as citric acid metabolism is linked to malic acid degradation.

Figure 1.

 

When present at low concentrations, diacetyl can contribute to the complexity of wine. Diacetyl has a buttery aroma which contributes to wine complexity when present at concentrations above its sensory threshold value of 0.2 mg/ℓ to 2.8 mg/ℓ. However, high diacetyl concentrations above 5 mg/ℓ can give rise to an overwhelming buttery aroma that masks the fruity and/or vegetative aromas in wines. Diacetyl can be reduced to the less sensory active acetoin and 2,3-butanediol (Figure 1) with much higher sensory thresholds of 150 mg/ℓ and 600 mg/ℓ, respectively. The reduction of diacetyl to these compounds is therefore encouraged during winemaking if a buttery style wine is not wanted. Several factors influence this reduction, as well as the sensory perception of diacetyl in wines.

A few of these factors include:

Composition of grape must

The grape must composition influences the concentrations, as well as the sensory perception of diacetyl. There are three main components of grape must that can influence the diacetyl concentrations during fermentation. These components are:

  • pH

Diacetyl is more rapidly reduced to acetoin during the fermentation of grapes from warm climate regions that have a higher pH. Wines from these regions might therefore have less diacetyl than wines from cool climate regions that are usually associated with a low pH.

  • Citric acid concentration

Grape must with a higher citric acid concentration leads to increasing concentrations of acetate, d-lactate, diacetyl, acetoin and 2,3-butanediol. Excess acetate and d-lactate causes over acidification and inhibits bacterial growth thus prolonging MLF. A longer MLF duration can result in more diacetyl being produced during the fermentation.

  • Phenolic compounds

Several studies have previously indicated that diacetyl in white wines was less stable and more likely to be reduced to acetoin and 2,3-butanediol than in red wines. However, the buttery aroma of diacetyl is more likely to occur in white wines than in red wines, due to the presence of phenolic compounds such as p-coumaric, caffeic, ferulic, gallic and protocatechuic acid. These phenolic compounds lower the buttery aroma in red wines by binding to diacetyl.

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Microbial strategies for wine ethanol reduction

by Debra Rossouw & Florian Bauer 

Introduction

A prominent goal in global wine research is the reduction of ethanol levels in wine, without the use of physical alcohol removal methods such as spinning cone columns and reverse osmosis (Howley & Young, 1992; Pickering, 2000). This research is motivated by a confluence of social, economic and environmental factors: On the one hand, many styles of wine that are popular in the global market require grapes to be fully ripe at harvest. Desirable levels of ripeness are frequently linked to high sugar concentrations in the grapes, which invariably, all other factors being equal, lead to higher final ethanol concentration in the wine. On the other hand, while achieving desired stylistic outcome, such high alcohol levels may negatively affect the taste and balance of the wine (Guth & Sies, 2002). From a health perspective, high ethanol levels add to concerns related to alcohol addiction and illnesses. Finally, many countries tax wine based on the percentage of alcohol creating a strong commercial incentive to decrease ethanol levels (Heux et al., 2006).

While pre- and post-fermentation processes have been considered in low ethanol research, a growing body of international research is targeting microbial technology in an attempt to alter fermentative ethanol production. Microbial strategies present an attractive opportunity to decrease ethanol levels while preserving the quality and aromatic integrity of the wine. One aspect of this research relates to yeast strain development through breeding or genetic engineering: The principle behind these approaches is the engineering of yeast strains through altered gene expression to modify carbon fluxes in the cell. One of the key target carbon sinks in these approaches has been glycerol, as several research groups have attempted to re-direct carbon towards glycerol in order to decrease the flow of carbon to ethanol. (Remize et al., 1999; Lopes et al., 2000). These approaches have seen some success in terms of decreasing the ethanol concentration in wine, but off-flavours, such as acetic acid and butanediol, are often produced. Rossouw et al. (2013) demonstrated that an alternative metabolite in central carbon metabolism, trehalose (a disaccharide made from two molecules of glucose), can be targeted as a carbon sink without resulting in the accumulation of undesirable redox-linked metabolites (Rossouw et al., 2013).

A second microbial strategy that has seen growing interest in the last decade involves the use of non-Saccharomyces yeasts in co-fermentation with conventional S. cerevisiae wine yeast strains. S. cerevisiae wine yeast strains have been selected for fermentation efficacy, and as such their primary fermentation kinetics (in particular ethanol yields) fall within a very narrow range. While finding S. cerevisiae strains showing lower than usual ethanol yields is thus not likely, this avenue can be pursued for non-conventional wine-associated yeasts where ethanol yields have been found to vary widely (Contreras et al., 2014; Rossouw et al., 2015). Several studies have reported lower ethanol yields when using non-Saccharomyces yeasts, however, the decreased ethanol production was often linked to high residual sugar levels in these wines (Ciani et al., 2006; Magyar & Toth, 2011). Recent studies have highlighted the diversity of the South African vineyard microbial landscape (Setati et al., 2012), providing the opportunity to access novel species and strains in the context of ethanol research.

Impact of yeast strain and environmental parameters on ethanol yields

Varying key environmental and fermentation parameters, such as must nitrogen content, pH and fermentation temperature, has been shown to significantly impact the production of key yeast metabolites such as glycerol (Rankine & Bridson, 1971; Torija et al., 2003). If glycerol production can be manipulated through environmental factors, and given that glycerol and ethanol production by yeast are often inversely correlated, ethanol production could likewise be manipulated. We therefore undertook to determine which fermentation factors (alone or in combination) could influence the production of ethanol. This systematic approach comprehensively investigated the effects of various combinations of pH, temperature and nitrogen settings on the ethanol yields produced by 15 commercial wine yeast strains. These experimental factors were selected as they can in principle be controlled by the winemaker, thus making implementation practical, cost-effective and user-friendly if successful. However, the data indicate that there are no statistically significant differences in ethanol yields between strains, or between different conditions …

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Taking a Good Look at Wine Labels

By Dr. Kathy Kelley

If a customer has never tasted the wine inside the bottle before “the label design and execution, as well as the verbiage,” can make or break a sale.  It is even suggested that at the point of purchase it only takes about 1.5 seconds for a wine label “to make an impact” on the consumer’s decision to purchase the bottle.

You may have wine labels that are well recognized and that your customers may respond, but it is also valuable to be aware of what some research suggests could attract consumer attention and what some brands are doing to encourage wine drinkers to “engage” with their bottle and (hopefully) share their experience with others.

Label illustrations, color, and design layout

While the “attractiveness” of a label is subjective, research has been conducted to identify label characteristics that appeal to consumers based on brand image (e.g., fun and whimsical) purchase intent (e.g., consumed at a restaurant, to give as a gift), and similar.

Screenshot 2017-06-16 11.18.18

Two University of California, Berkeley, researchers conducted a study during which participants evaluated wine labels to measure California Cabernet Sauvignon purchase intent based on six label colors, five illustrations, and three design layouts (Boudreaux and Palmer, 2007).  The researchers developed and tested 90 fictitious labels with the same brand name, origin, vintage, and alcohol content.  Though the images are black and white and only a subset of the 90 labels is presented you can get a sense of what the labels looked like by accessing the paper here: http://bit.ly/2swFQUg.

Their results revealed that the illustration presented on the label had the strongest effect on “market success factors and on brand personality” and in general the images that received the highest purchase intent scores were: 1) grape motifs and 2) images of a chateaux or vineyards.  However, if the brand’s goal is to develop a label to convey “upper class and value,” results suggested that a coat-of-arms illustration would be the best option.

The researchers reported that of the colors they tested, burgundy, red-orange, and neutrals “were seen as successful, desirable, and expensive.”

Millennial preferences

While the UC Berkeley study did not segment the data based on generation to learn what Millennials might prefer compared to older generations, such data has been published.

A 2015 Gallo Consumer Wine Trends Survey revealed that the label is important to Millennials, and wine drinkers in this generation are “4X more likely than Baby Boomers to often select a bottle of wine based on its label” (http://gallowinetrends.com/home/).  While the younger generation is “more likely to look for” labels with personality and originality, Baby Boomers look for information on labels that describe the region of origin and taste descriptors.

Elliot and Barth (2012) focused on understanding Canadian Millennials’ preferences for wine label design and personality. Participants, mostly 19 to 22-year-old undergraduates, were asked to list the most significant factor that influenced their wine purchasing decision.  Of the factors listed, 86% of the total mentions referred to an extrinsic [the package] factor (e.g., name of the wine, design layout, bottle) with 33.8% of all the mentions related to the “label,” followed by other “package elements,” color(s) (10% of the mentions), design (9.8%), the bottle (9.3%), and the image (9.1%).

Only 14% of the mentions pertained to intrinsic [the product] factors with the top three mentions being: the producer (6.1% of all mentions), type of wine (3.4%), and alcoholic degree (2.2%).  The researchers indicated that though the emphasis, at this point in their drinking career, is on extrinsic factors – it may be possible that “opinions and preferences” may shift to intrinsic factors as they age and their experience with drinking wine increases.

Participants were then asked to assign ratings to indicate how influential (1= not at all influential to 5 = extremely influential) six packaging characteristics were on their bottle selection.  The top three influential characteristics (rated between 3.83 to 4.00) were: label image or picture, design layout, and color.  Name of the wine, description of the wine, and shape of the bottle were less influential.  The authors point out that price was not tested, but if it was it probably would have “had a significant influence.”

Trying to learn what label factors appeal to certain generations is not restricted to just New World wine brands. Some wineries Bordeaux are designing labels that (hopefully) appeal to younger wine drinkers.

According to an article published in February 2017 (http://bit.ly/2sxYH10), the author interviewed two Bordeaux label designers about their approach to designing “non-traditional” labels.  One designer is quoted as saying, “The new generation of Bordeaux winemakers…[are] trying to break out from overwhelming history” by using “‘avant-garde’ design approaches.”  Another designer and the winemaker at Château Chasserat created a non-traditional wine called Père N 1775 (which includes the French word for father and the year the winery was created).  The associated logo has more of an Aztec feel/look than that of château or vineyard you would expect to see on a traditional bottle of Bordeaux.

Cultural influences

It is important to note that generation is not the only demographic that could impact response to wine labels, or any extrinsic or intrinsic characteristic.  Culture has been studied by a few researchers to learn how it may affect response to a wine brand, promotional approach, label/bottle characteristics, etc.

Lockshin and Cohen (2009) investigated what influenced consumers from 11 countries when purchasing wine.  Though examples of wine labels were not presented, participants were asked to indicate the relative importance of “an attractive front label,” in addition to 12 other factors (e.g., the origin of the wine, grape variety, promotional display in-store).

Participants were segmented into three groups based on their responses to survey questions.  While the smallest of the three groups, 16% of survey participants, one of the segments was based on making wine purchasing decisions based on displays, attractive front labels, and back labels.  A quarter of respondents from the UK were in this group, with slightly fewer Austrians (22.5%), Germans (20.9%), participants from the USA (16.4%), and Brazilians (15.4%) belonging.  Ten percent or fewer of participants from Australia, France, Israel, Italy, and New Zealand, and Taiwan were assigned to this group as larger percentages of these consumers made choices based on recommendations/previous experience or based on variety, origin, brand name, and awards.

“Cool” and interactive wine labels  

Last year, Pace Magazine published a list of seven wine bottles with labels that drinkers could play with, including one that revealed a “secret message” when a little bit of wine is poured on it and another that had a pull tab that served as a wishbone (http://bit.ly/2sx46qe).  Add to this the other online sources that create their own annual lists: Tasting Table (http://bit.ly/2tuwllM), Forbes (http://bit.ly/2tuzkuB), BuzzFeed (http://bzfd.it/2tuy3U2), and many others.

While the graphics, layout, and colors used on the label certainly attract purchasers, there are several brands that have added a Quick Response code (QR code; http://bit.ly/2std07Q) to their label.  The code, when scanned with a smartphone QR code reader, directs the consumer to a website with other pertinent information about the winery, the particular wine in the bottle, videos, social media sites, or anything that the winery decides.

One such brand is Brancott Estate in Marlborough, New Zealand.  The company developed the “Brancott Estate World’s Most Curious Bottle” app (http://bit.ly/2st5sC3) in 2012 so that wine drinkers could “interact” with bottles of their Sauvignon Blanc.  I have included some screenshots that I took while I was using the app, below.

Screenshot 2017-06-14 13.41.02

While I did have a bottle of the wine that I could use for this demonstration, if you do not have one you can use a picture of the bottle/QR code (from one of their magazine advertisements, for example) and certain app activities are available on app even if do not have a bottle/photo.

A Spanish wine brand, Bodegas Vihucas (Toledo, Spain) has created a blend of Tempranillo, Merlot, and Graciano called 8 TICKETS(http://www.8tickets.es/el-vino/; retail price of 9.60 euros).  The label is a metro map that when removed from the bottle (held in place with two stickers), after which it becomes a “game board.” includes directions on how to play the game, and has a space for the drinker(s) to color, draw, and decorate with stickers.

While I don’t have a picture of the bottle/label/game board, as the wine is only available a few Spanish markets (http://8tickets.es/localiza-tu-tienda/), they do have a Facebook Page with reviews (https://www.facebook.com/8tickets/) and Instagram account with images of the bottles and groups of drinkers having fun with the label/game board (https://www.instagram.com/8tickets/).  I did contact the brand and was informed that 8 TICKETS will be available in the U.S. “soon.”

As you might expect, the 8 TICKETS concept and label was developed to appeal to the Millennial wine drinker.  Specifically, the aim of the 2016/2017 A’Design Award & Competition Packaging Design Category winner was to “bring wine to [Millennials] through a memorable and participative experience…show young people all the situations in which wine can be a regular consumption product rather than being reduced to [only being drunk on] special occasions” (http://bit.ly/2sYyvKL).

If you would like to learn about wine and alcoholic beverage product and packaging trends as soon as items launch, visit Trendhunter.com.  You can learn about the new Coors Light can that changes colors when exposed to UV light rays (currently available in the Canadian market, http://bit.ly/2sYxwdM), Croatian wine that is aged in the Adriatic Sea in glass and clay vessels for 2 years at a depth of 20 meters (http://bit.ly/2sYveeu), and drinkable glitter flakes with a “subtle raspberry flavor” that can be added to a glass of prosecco for an even more sparkling wine (http://bit.ly/2sYhv7r).

What is presented in this blog post is just a small portion of the studies and examples of wine labels/bottle characteristics that appeal to consumers.  At Penn State, we have conducted several studies that investigated consumer response to a number of different wine bottle components.  Among the data that we have published in this blog, one study, in particular, focused on what information and features a winery should consider including on the back label (http://bit.ly/2sxTre7).  As with other marketing information we post, it is crucial to understand who your customer is and ask them to respond to your label ideas before making any significant changes or investments.

References

Boudreaux, C.A., & Palmer, S.E. (2007). A charming little cabernet. International Journal of Wine Business Research, 19(3), 170-186. doi:http://dx.doi.org.ezaccess.libraries.psu.edu/10.1108/17511060710817212

Elliot, S., & Barth, J.E. (2012). Wine label design and personality preferences of millennials. The Journal of Product and Brand Management, 21(3), 183-191. doi:http://dx.doi.org.ezaccess.libraries.psu.edu/10.1108/10610421211228801

Lockshin, L. & Cohen, E. (2009). Using product and retail choice attributes for cross-national segmentation. European Journal of Marketing, 45(7/8), 1236-1252.

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How to reduce the pinking potential of white wines

By Anton Nel of Wineland Magazine

When white wines with the potential to pink are exposed to oxygen, the phenomenon known as pinking occurs. It is common in Sauvignon blanc, but also occurs in Chardonnay, Colombar, Chenin blanc and Viognier.

Literature exists about the possible compounds and components that promote pinking, but not all findings concur and there is still much uncertainty about the cause of the phenomenon. Research into pinking is therefore ongoing. The following is a discussion of basic guidelines to reduce the pinking potential of white wines, but research is currently in progress and more comprehensive feedback will be given to the industry at the end of the study.

 

Reductive vinification

During reductive vinification the winemaker tries to eliminate oxygen (O2) as much as possible. The most common ways of doing so entail working with dry ice, inert gas or ascorbic acid. When ascorbic acid (vitamin C) is used during the winemaking process, the ascorbic acid is oxidised into dehydroxy ascorbic acid and hydrogen ions. In the presence of oxygen in the juice/wine the oxidation of ascorbic acid also results in the formation of hydrogen peroxide (H2O2). This is a strong oxidative agent and SO2 is required to bind to it and neutralise it.

 

Keep the following guidelines in mind:

  • It is important always to keep the free SO2 concentration of the wine as close as possible to 35 – 45 mg/ℓ when working with ascorbic acid.
  • As soon as dry ice and inert gas are involved, it is important to keep the SO2 of the wine as close as possible to the above-mentioned values.
  • Ascorbic acid reacts with SO2 at a ratio of 1:1.7 and not 1:1 as generally accepted. It is therefore important first to determine the existing concentration of ascorbic acid in the wine before making any ascorbic acid additions or adjustments.

 

Metals in wine

Much research has been done on the effect of heavy metals (Cu, Fe) in wine. It is always good to analyse the wine for heavy metals and if the metal content is high, the free SO2 levels should be kept at a minimum of 45 mg/ℓ.

 

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Ensure Your Wines are Stable Before Bottling

It’s that time of year again: bottling time! The past year’s vintage is slowly starting to take up too much room in the cellar and now is the time for decision making in terms of preparing for the pending vintage.  Finalizing a good bottling schedule before harvest starts is an essential good winemaking practice, but bottling comes with its own set of challenges.

It is not uncommon for winemakers to express feelings of “not being able to sleep at night” when wines get bottled, as they are worried about possible re-fermentation issues.  As wine naturally changes through its maturity, it is easy to feel insecure about bottling wines, especially those wines that may have had challenges associated with it throughout production.

However, there are several analytical tests that winemakers can add to their record books every year to ensure they are bottling a sound product.  The following briefly describes a series of analytical tests that provide information to the winemaker about stability and potential risks associated with the product when it goes in bottle.

Bottling comes with its own set of challenges and risks, but several analytical tests can help put a winemaker’s mind to ease regarding bottle stability. Photo by: Denise M. Gardner

Basic Wine Analysis Pre-Bottling:

This first list is the bare minimum data that should be measured and recorded for each wine getting bottled, regardless of the wine’s variety or style.  Keeping accurate records of these chemistries is also helpful in case something goes wrong while the bottle is in storage or after it is purchased by a customer.

pH

pH is essential to know as it gives an indication for the wine’s stability in relation to many chemical factors including sulfur dioxide, color, and tannin.  For example, high pH (>3.70) wines provide an indication that more free sulfur dioxide is needed to obtain a 0.85 ppm molecular free sulfur dioxide content.  At the 0.85 ppm molecular level, growth of any residual yeast and bacteria in the wine should be adequately inhibited.

High pH wines tend to have issues with color stability.  At this point, color stability can be addressed by blending or with use of color concentrates (e.g.,Mega Purple).  Keep in mind that if the wine is blended with another wine, all chemical analyses, including pH, should be completed on the blend (as opposed to average individual parts) prior to bottling.

Free and Total Sulfur Dioxide Concentration

In the United States, total sulfur dioxide is regulated and must fall under 350 mg/L for all table wines (CFR: https://www.ecfr.gov/cgi-bin/text-idx?SID=eddaa2648775eb9b2423247641bf5758&mc=true&node=pt27.1.24&rgn=div5#sp27.1.24.a).

However, the free sulfur dioxide concentration provides an indication to the winemaker regarding antioxidant strength and perceived antimicrobial protection.  To inhibit growth of yeast and bacteria during bottle storage, a 0.85 ppm molecular free sulfur dioxide concentration must be obtained.  The free sulfur dioxide concentration required to meet the molecular level is dependent on pH.  Therefore, free sulfur dioxide additions should be altered and based on a wine’s pH for optimal antimicrobial protection.

Analytically, it can be daunting to measure free sulfur dioxide as the wet chemistry set up looks intimidating.  However, many small commercial wineries have benefited from the integration of a modified aeration-oxidation (AO) system, and with a little practice, have been relatively successful at monitoring free sulfur dioxide concentrations.  A few wineries have worked to validate use of Vinmetrica’s analyzer (https://vinmetrica.com/), and found results comparable to those obtained by use of the AO system.

Residual (or Added) Sugar

Any remaining sugar in the bottle, whether through an arrested fermentation or direct addition, can pose a risk for re-fermentation post-bottling.  This is especially true if the winery lacks good cleaning and sanitation practices.  Nonetheless, it is a good idea to assess the sugar content pre-bottling to record a baseline value of the sugar concentration going into bottle.  If bottles were to start re-fermenting, a sugar concentration could be analyzed and used to compare against the baseline value in order to assess the potential of yeast re-fermentation.

For wineries with minimal residual sugar concentrations, a glucose-fructose analysis (often abbreviated glu-fru) is often used to help determine accurate sugar content.  For wines with added sugar an inverted glucose-fructose analysis may be required.

If you are concerned about potential risk for Brettanomyces (Brett) bloom post-bottling, it is usually encouraged to reduce the sugar content in the finished wine below 1% (<10 g/L sugar) in the bottle.

Malic Acid Concentration

While using paper chromatography to monitor malolactic fermentation (MLF) is useful, it does not give an accurate reflection of residual malic acid concentration.  In fact, some winemakers find that a paper chromatogram may show a MLF has been “completed,” but would prefer to have lower residual malic acid concentrations remaining in the wine.

During my time at an analytical company, 0.3 g/L of malic acid and below was considered “dry.”  This is typically a safe level of residual malic acid to avoid post-bottling MLF.

Volatile Acidity

Volatile acidity (VA) is federally regulated, and levels are indicated in the Code of Federal Regulations (CFR: https://www.ecfr.gov/cgi-bin/text-idx?SID=eddaa2648775eb9b2423247641bf5758&mc=true&node=pt27.1.24&rgn=div5#sp27.1.24.a).  For most states, with California as an exception, the maximum allowable VA for red wines is 1.40 g/L acetic acid (0.14 g/100 mL acetic acid) and for white wines is 1.20 g/L acetic acid (0.12 g/100 mL acetic acid).

Monitoring VA through production is a good indicator of acetic acid bacteria spoilage.  At minimum, wineries should record VA

  • immediately post-primary fermentation,
  • post-MLF,
  • periodically through storage (e.g., every 2-3 months) and
  • pre-bottling.

Whiling monitoring VA, sharp increases in VA should alarm the winemaker of some sort of contamination.  Typically, these increases are caused by acetic acid bacteria, which can only grow with available oxygen.

Alcohol Concentration

As a general rule of thumb, knowing the final alcohol concentration is a good idea.  Alcohol content helps determine a tax class for the wine and is required for the label.

 

Extra Analysis:

Titratable Acidity (TA)

All wines are acidic in nature as they fall under the pH 7.00.  However, titratable acidity (TA) acts as an indicator for the sour sensory perception associated with a given wine.  For example, two wines, Wines 1 and 2, with a pH of 3.40 may have different TAs.  If Wine 1 has a TA of 8.03 g/L tartaric acid while Wine 2 has a TA of 6.89 g/L tartaric acid, Wine 1 would likely taste more acidic (assuming all other variables are the same).

Titrations are an easy analytical testing method to learn and understand when testing wine’s chemistry. Photo by: Denise M. Gardner

Cold Stability

Cold stability tests are often recommended to ensure the wine is cold stable, and will, therefore, not pose a threat of precipitating tartrate crystals during its time in bottle.  Not all wines require a cold stability process (e.g., seeding and chilling).  Cold stability testing can be done prior to a cold stabilization step in order to avoid extraneous processing operations, saving time and money.

For more information on cold stability processes and testing, please visit Penn State Extension’s website: http://extension.psu.edu/food/enology/analytical-services/cold-stabilization-options-for-wineries

These crystals on this cork illustrate what can happen when a wine is not properly cold stabilized. While the tartrate crystals pose no harm to consumers, they may find the crystals unappealing or questionable. Photo by: Denise M. Gardner

Protein Stability

Additionally, haze formation is a potential risk post-bottling.  While hazes do not typically offer any safety threat to wine consumers, they often look unappealing.  Protein hazes tend to make the wine look cloudy.  Some varieties are more prone to protein hazes then others, and running a protein stability trial could minimize the risk for a protein haze in-bottle.

It is important to remember that due to the fact protein stability is influenced by pH, cold stability production steps should take place before analyzing the wine for protein stability and before going through any necessary production steps to make the wine protein stable.  This is due to the fact that cold stability processes ultimately alter the wine’s pH, and the chemical properties of proteins are influenced by the pH.

 

Analysis for Those that May Consider Bottling Unfiltered:

Yeast and Bacteria Cultures (Brett, Yeast, Lactic Acid Bacteria, Acetic Acid Bacteria)

Having a microscope in the winery can be a great reference point in terms of scanning for potential microbiological problems.  However, if the winery does not have a microscope, but knows that some microbiological issues or risks may exist in a wine, having a lab set test the wine on culture plates is a good indicator for potential growth risks during the wine’s storage.

If the wine is going to be bottled using a sterile filtration step, keep in mind that wines are not bottled sterile.  Assuming the absolute filtration method is working properly, the wine has potential to become re-contaminated with yeasts and bacteria from the point of which it exits the filter.  In fact, it is not uncommon for wines to pick up yeast or bacteria contamination during the bottling process.

Managing free sulfur dioxide concentrations can help inhibit any potential growth from contamination microorganisms if the proper antimicrobial levels (0.85 ppm molecular) are obtained at that wine’s pH and retained during the bottle’s storage.

4-EP and 4-EG Concentrations for Reds

For wines that may have had a Brettanomyces (Brett) bloom, knowing the concentrations of 4-EP and 4-EG in the wine going into bottle is a good result to keep on file.  If a Brett bloom occurs later in the bottle, it is likely (although, not guaranteed) that the volatile concentration of 4-EP and/or 4-EG may increase and confirm the problem.

Furthermore, evaluating a wine for 4-EP and 4-EG concentrations can also help isolate a possibility of Brett existence, especially if their concentrations are below threshold.  However, it should be noted that both compounds can also exist in wines that are stored in wood, even without a Brettcontamination.

Double Check: PCR for Reds

Brett can be a tricky yeast to isolate and identify.  It is usually recommended to run multiple analytical tests related to Brett in order to confirm its existence or removal from a wine.  While culture plating identifies living populations of microorganisms, PCR cannot typically differentiate between live and dead cells as it is measuring the presence of DNA.  A microorganism’s DNA can get into a wine after yeast death and through autolysis.  Therefore, a positive PCR result for Brettanomyces is hard to confirm if the result includes live cells, dead cells, or a combination of both.

Culture plating can help confirm the presence of active, live cells, but the success rate of growing Brettanomyces in culture plates is variable.

Nonetheless, scanning wines by PCR for Brett can help winemakers isolate a general presence and risk of Brett in their wines.

Wine samples prepare for analytical evaluation. Photo by: Denise M. Gardner

Still Worried About Your Wine Post-Bottling?

Bottle sterility

Bottle sterility testing is helpful, especially when a winemaker wants to ensure wines have been bottled cleanly.  For this type of testing, it is best to sample a few bottles

  • at the beginning of a bottling run,
  • immediately before any breaks,
  • immediately after any breaks, and
  • at the end of a bottling run.

Bottles can, again, be evaluated under a microscope and evaluated for the presence of microorganisms.  Bottles can also be sent to a lab for culture plating.  The growth of yeasts or bacteria from culture plates at this stage indicates a failure of the sterile filtration system or contamination of the wine post-filtration.  Clean wines, obviously, should help put a winemaker’s mind at ease as it matures in bottle.

Ensuring a wine’s stability post-bottling is a challenge.  However, with proper cleaning and sanitation methods coupled with the right analytical records, winemakers can reduce their worry.  For information on any of these topics, please visit:

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Skin-fermented white wine – all talk and no action?

When I started writing this blog, an old adage came to mind, “there is more than one way to skin a cat”. If you believe thatthere are many different ways to achieve an objective and that the reason for drinking wine is enjoyment, then skin-fermented wines could be the means to an end.

I tasted skin-fermented white wine (henceforth referred to as orange wine) for the first time in Croatia last year and during that tasting surmised that this type of wine is not for everybody. My second experience with orange wine was last week at a wine tasting chaired by James Pietersen of Wine Cellar (Observatory, Cape Town). During this tasting I was bombarded with so many new (and sometimes weird) aromas, that I soon realised that I was out of my depth. Take a look at Table 1 at the end of this blog for more details.

After the tasting, Edo Heyns (also present at the tasting) and I discussed the wines and he reckoned that this was probably the most difficult tasting that I could have kicked off with (I started at WineLand on 1 February 2017). Edo supplied this quote, “This burgeoning niche category offers some truly delicious wines. Chenin Blanc has particularly risen to the occasion, but there are also impressive blends and Sauvignon Blancs made in this style. The tasting yielded an intriguing list of descriptors and discussions, which is part of the category’s appeal. I specifically enjoyed wines that had a neat balance of texture and acidity. Judging this style definitely tests your tolerance for funkiness. While this is part of the excitement, it could also be its Achilles heel. Skin-fermented wines should first and foremost be good wines. To me, that was not the case for some of the wines in the line-up.”

And judging by how well some of these wines are selling locally, regardless of the relatively higher price, orange wine is doing a lot of well-placed scratching. Speaking of price, these five wines ranged from R135 to R275. While a lot is said about orange wines and their sometimes obvious faults, consider that one of the browner wines at this tasting scored quite well, because of the nose and palate. As it turns out, one cannot solely judge a book by its cover (I’m on a roll with proverbs today …

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