Winetech Technical Yearbook 2022

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species and some Lactobacillus species, are the main culprits when it comes to high VA levels found in grapes and juice even before arrival at the winery. Add to this the heatwave that was mentioned earlier and you could potentially have a ticking VA bomb at hand, given the link between microbial spoilage and high temperature. CONVENTIONAL TACTICS AGAINST HIGH VA Vigilance during challenging winemaking conditions, such as heatwaves and less healthy fruit, remains key. Therefore, monitoring the VA of must during fermentation, and throughout maturation, is good practice. Winemaking lore is also very clear on excessive temperatures, oxygen, ullage, residual sugar and insufficient SO 2 . The topping of barrels and tanks, as well as maintaining adequate molecular SO 2 levels are but two ways of controlling a pesky microbe such as Acetobacter aceti – a rapid producer of acetic acid and fan of oxygen. Apart from the negative organoleptic impact of high VA on wine, it can also hinder AF. A stuck wine with a VA concentration above 0.8 g/L will have to be blended or treated with reverse osmosis to drop the VA concentration to an acceptable level, after which AF can be restarted. TAKING THE FIGHT TO VA WITH BIOCONTROL One might say that a shortcoming of the tried and tested tactics mentioned above is that they do not start the fight against VA early enough. This is where the concept of bioprotection is more proactive. Selected commercial strains of Torulaspora delbrueckii and Metschnikowia pulcherrima with low fermentation activity can literally plant their flags in microbial no man’s land. Otherwise put, the early colonisation of grapes, harvesting machines, containers, and other grape transportation vessels by selected T. delbrueckii and M. pulcherrima strains limits the growth of potential spoilage microorganisms. The bioprotection these strains offer, continues until AF for white and red wines. Not too bad, right? EARLY BIRD CATCHES THE “VA”RM To summarise all of this, winemakers cringing at the thought of musts with high VA, especially during heatwaves, can dry pitch or spray biocontrol yeast strains on their harvesting equipment and transport vessels to minimise VA production by spoilage microbes. And now you will never think of the phrase, Va Va Voom, the same again. REFERENCES https://www.wineland.co.za/hot-vineyards-not-that-va-va voom-after-all/

HIGH TEMPERATURES, GRAPES AND SPOILAGE MICROBES – A VOLATILE COMBINATION VA (volatile acidity) in wine is a given, with a concentration of 0.6 g/L or lower quite normal. Saccharomyces cerevisiae produces 0.2 - 0.5 g/L VA during alcoholic fermentation (AF) and lactic acid bacteria 0.15 - 0.3 g/L VA. But what about elevated VA levels before the grapes reach the winery? Bird peck and sour rot are examples of physical damage to grape berries that exposes sugars to various bad characters that lurk in vineyards. Spoilage bacteria, such as Acetobacter

For more information, contact Bernard Mocke at bernard.mocke@laffort.com.

Common sources and levels of volatile acidity in wine.

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WINETECH TECHNICAL YEARBOOK 2022