Analytical testing during aging… Is it important? What is its purpose? Too often in the laboratory, we see problems that could have been easily avoided by a simple monitoring or pre-bottling analysis. In complicated years like this year, where humid temperature during summer months had a significant effect on microbial flora, we notice high amounts of acetic acid at the end of alcoholic fermentation, even before aging begins. In this short article, we will talk about the best practices to adopt during aging and efficient risk management.

Main Problems During Aging

Harvest is over, fermentations are done or they are close to be.  Everything sits well in tanks or barrels.  However, the work is far from being over.  The winery enters a critical production step: aging.  During this step, wines or ciders are transferred to stainless steel or concrete tanks, barrels or other containers in order, for the producer, to achieve his or her vision.  During aging, tannins will soften, aroma will develop.  It is at this critical step where faults can develop.

  • Reduction aromasReduction may be the result of sulfur-based compounds like H2S produced at the end of alcoholic fermentation under low oxygen conditions. During wine maturation, lees may also contribute to the production of mercaptan, a molecule responsible for the aroma of rotten eggs.  This is why white wines are quickly transferred to holding tanks in order to stabilize them.
  • Volatile Acidity : The occurrence of acetic acid, the main component of volatile acidity, depends on several factors. The health status of the grapes during harvest plays a big role. Also, if a significant number of bacteria are present during the alcoholic fermentation step, there is an increased risk of acetic acid production, even before the end of fermentation.  As the current trend in the industry is to limit the use of sulfites as much as possible after the fermentation steps, this places wines and especially ciders at risk of increased acetic acid production, particularly if sugars and malic acid are present.  These molecules are perfect substrates for bacteria.  Finally, acetic acid, when found in significant amount, will react with ethanol to form ethyl acetate which is responsible for nail polish aromas.
  • Brettanomyces Brettanomyces type yeasts are naturally present in the environment and on grapes.  Unlike other wild yeasts, they have an excellent tolerance to high levels of alcohol, much like Saccharomyces yeasts which are used for fermentation.  Brettanomyces yeasts persit easily in winemaking installations and in barrels.  They are at the source of several wine faults as they produce a variety of secondary metabolites such as 4-ethyl phenols and 4-ethyl guaiacol.  These molecules are responsible for “horse sweat”, “leather” and wild type aromas.  Brettanomyces yeasts are very sensitive to sulfites and as the use of sulfites decreases, risks of faults caused by these yeasts increase.
  • Oxidation : Reducing the use of sulfites has another consequence.  It can lead to wine oxidation. Sulfites serve as antioxidants and inhibit bacterial proliferation. Although oxidation is a component of the aging process, if it’s not controlled, it can cause alterations in colour and aroma loss. Wines, especially those aged in barrels, are particularly susceptible. Furthermore, oxygen can facilitate the conversion of ethanol into acetaldehyde.

Risk management during aging

The aging period offers a crucial opportunity to improve the quality of wine or cider. While the tasting process remains the most effective and preferred way to manage risks during this stage, analytical testing will provide more precise information on the present state of the wine or cider.  Producers are strongly encouraged to taste their products at regular intervals to detect any changes in organoleptic properties. In reasonable risk management, it is also advised to use a professional taster like an oenologist. Oenologists have an increased sensitivity to certain molecules, such as volatile phenols. Analytical monitoring can complement tasting, particularly the monitoring of acetic acid, volatile acidity, and sulfites to comply with legal standards. The laboratory can also carry out a total count of Brettanomyces type yeasts to identify any potential contamination.

You would like to send a sample for analytical testing during aging? Please fill out our Analytical Request Form and forward your samples to Laboratoire OENOSCIENCE, 2050 Dandurand suite 308, Montreal, Quebec, H2G 1Y9.  You can always contact us directly at 514-564-2050.

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