Technical Yearbook 2023

MARCH

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Making a Top 10 Merlot – to cold soak or not By Karien O’Kennedy

The start of any great wine is in the vineyard, the specific terroir coupled with the specific viticultural practices employed. However, more than exceptional grape quality is needed to guarantee a great wine since winemaking is an interventionist process, and every step of the process requires the skill and experience of a winemaker. If a winemaker makes the right choices given the characteristics of the grapes received, only then is the extraordinary achieved. One of these choices is whether to cold soak (cold macerate) grapes before fermentation. What is cold soaking and why do winemakers do it? Cold soaking is believed to have originated as a technique to improve the colour of Pinot noir wines. According to a relatively recent academic review article by Dr Jose Luis Aleixandre-Tudo and Prof Wessel du Toit (2018), the main reasoning behind cold soaking is that during the pre fermentative period, phenolic compounds are transferred from the solid parts of the berry into the must under low temperatures (to prevent the start of fermentation) and in an alcohol-free environment (aqueous media). This can potentially enhance the phenolic content of the final wines. Cold soaking is not restricted to Pinot noir anymore. Winemakers worldwide employ this technique for various reasons on many cultivars, including Merlot.

What the science says The two researchers mentioned above systematically reviewed the scientific literature on cold soaking reported during 2006 - 2017. They found that the cultivar, the vintage, the climate, the vineyard, the grape’s ripening status, initial phenolic composition, grape wall composition, cold soaking temperature, length of cold soaking, cold soaking with or without enzymes, dry ice and sulphur dioxide (SO 2 ), play significant roles in the efficacy of this technique. Many factors, therefore, influence the outcome of cold soaking, and a positive result is not always the case. Some studies reported an initial increase in phenolic concentrations after cold soaking, but this increase disappeared with ageing. Since cold soaking entails various logistical and economic considerations, one must ask oneself, is it worth the effort? What the Top 10 Merlot winemakers have to say During 2022 the first Top 10 Merlot competition was organised by the South African Merlot Forum, also known as Hallo Merlot. Nine of the Top 10 Merlot winemakers were interviewed about their specific choices while producing their award-winning wines. They were questioned whether they employed cold soaking and, if they did, how it was performed and what they believed they got out of it. Four of the nine winemakers used cold soaking when they produced the specific Merlots that won the 2022 competition. Reasons given by the other winemakers not doing cold soaking, include not having the capacity to keep the must very cold for an extended period, not being convinced that it adds something to the wine and the danger of non Saccharomyces yeasts proliferating during cold soaking and thereby removing much-needed nutrients, for the

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TECHNICAL YEARBOOK 2023