In the production of wine we talk about 2 separate fermentations. The first fermentation (with which I’m sure you are all familiar), is alcoholic fermentation. This is when the sugar in the grape juice is transformed into alcohol by the yeast (either natural yeast on the bloom of the grape or added yeast). The by-product of alcoholic fermentation is CO2 and this is what gives the fizz in sparkling wines.
There is also a second fermentation called malo-lactic fermentation (sometimes called malo or MLF). This is more of a bacterial transformation during which the naturally present malic acid in the wine (the kind of acid that you find in a Granny Smith apple) is transformed into a softer acid called lactic acid (the kind of acid you find in milk). It normally happens after the alcoholic fermentation has finished but can also occur at the same time. The result of this malo-lactic fermentation is a drop in acidity in the final wine.
Here in the Loire and indeed around the world, reds routinely go though ‘malo’. Grapes grown in cooler climates tend to have higher levels of malic acid than those grown in hotter climates and so the resulting drop in acidity is more marked. Whites however vary – some whites from the Loire go through malo and others will not. Sometimes a producer will actively stop it from happening (it’s often spontaneous) as they wish to keep a high level of acidity and freshness in the wine.
As with alcoholic fermentation (when more natural winemakers will rely on the naturally present wild yeast population on the grapes and in the winery), the bacteria required for this process to happen are naturally present although growers can add a commercially prepared additive.
One of the by-products of malo-lactic fermentation is diacetyl, an organic compound (CH3CO)2 that has a strong buttery flavour. Have you ever wondered why your oaky Chardonnay tastes so buttery? Well this is because of malo-lactic fermentation! Some producers promote the production of diacetyl in the winery to impart the rich mouthfeel and flavour that it produces. This is particularly pronounced and integrated into the wine when the MLF takes place in oak barrels.
CO2 is also a by-product of MLF and so it’s important that is it either blocked or finished in a bottled wine to avoid any secondary fermentation in the bottle itself (which would result in a fizzy, cloudy wine).
Cultured cream, butter and buttermilk owe their tartness, buttery flavour and aroma to diacetyl. It is also added to artificial spreads and butter replacements to make it taste like butter.
