WINETECH Technical Yearbook 2021

Anthocyanins can also be stabilised by other phenolic molecules such as tannins, which act as co-pigments allowing them to associate and form a ‘stack’ of molecules in the must or wine. These stacks then condense and associate further becoming even more stable as they get larger. Great, the poor wine colour problem is solved. Not so fast...what happens if the tannins are so stable that they don’t even leave the grape? EXPLAINING THE PROBLEM Tannin transfer from the grape skin and seeds to the final wine can be hindered by the tannins forming strong associations with polysaccharides in the grape cell wall, as well as soluble polysaccharide polymers present in the must and wine. In a dramatic turn of events, the same associations of stacking and condensation responsible for stabilising the final wine colour, now hinder these compounds from being released from the grape berry. Alas, the content of these phenolic compounds in the wine is diminished, bearing no awards for the winemaker and no pleasure for the wine drinker. PRESENTING THE SOLUTION Fret not! Once again, our winemaker has covered all bases to ensure enough polyphenol extraction: from intricate pressing, cold soaks, longer macerations

to vigorous punch-downs and pump- overs. These are all methods adopted to improve the extraction of tannins and other polyphenols, but perhaps the greatest tools the winemaker possesses are macerating enzymes. These enzymes offer many advantages including accelerated settling, clarification and increased juice yield. But of interest to our winemaker, are the enzymes that degrade the associations of polyphenols with polysaccharides in the grape cell wall, encouraging the release of the phenolic compounds from the grapes and into the wine. Research in this area of enzymes is active and much is still to be understood. Most enzymes are isolated from a diverse range of fungi . Enzyme preparations often contain pectinases – which break down the scaffolding between cells in the grape berry cell wall, as well as cellulases and proteases – which break down other structural components in the berry cells. The result of adding these enzymes is an increase in anthocyanins and other polyphenolics such as tannins, thereby improving colour, aroma and mouthfeel in the wine. Enzymes are usually dissolved in distilled water and added to the wine must soon after crushing. However, the degradation of the cell wall is a tough job and it requires the cooperation of several pectolytic enzymes to be effective.

such as anthocyanins. However, in this case, the tannins should complement the wine rather than deter the drinker. The magic of wine tannins operates through the positive influence on the mouthfeel, taste perception and complexity of the wine – they also have an important antioxidant role. ABOUT ANTHOCYANINS Anthocyanins are key colour polyphenols in red wine and are named according to their first detected source. An example is pelargonidin, an orange-coloured anthocyanin first isolated from the Pelargonium flower. Anthocyanins are produced during grape ripening at the start of véraison where they accumulate in the skins of the berry. In winemaking, the extraction of anthocyanins occurs

during maceration and peaks before the end of fermentation, and gradually declines thereafter. Tannins, however, continue to be extracted well after fermentation. Anthocyanins are extremely sensitive to pH and need to be stabilised by other compounds or they will degrade thereby destroying their colour. The question then arises: how can anthocyanins be stabilised to preserve colour? ON STABILISING COLOUR Winemakers have a few tricks up their sleeve when it comes to stabilising anthocyanins. These include keeping the wine at a pH of between 3.2-3.6 and controlling the amount of sulphur dioxide added, which can have a bleaching effect. These actions maintain the dark red/violet colours of the all-important anthocyanins.

WINETECH TECHNICAL YEARBOOK 2021 | 62