Malolactic conversion, known as malolactic fermentation, often shortened to MLF or malo, is the conversion of the more aggressive malic acid naturally present in new wine into lactic acid (which has lower acidity) and carbon dioxide. It is accomplished thanks to the lactic acid bacteria naturally present in a winery (otherwise cultured LAB is added to the wine). This process is unrelated to the first, main alcoholic fermentation (the process of converting sugar to alcohol and carbon dioxide by the metabolism of yeast). Hence, it is sometimes called secondary fermentation. In a healthy winery environment malolactic conversion follows naturally by the end of the alcoholic fermentation.
Why malolactic conversion
It adds flavour and complexity to both red and white wines. The texture becomes softer and silkier. It adds to a more rounded, full-bodied wine.
Another aspect is health and let me briefly make a digression... we are organic for the benefit of our land and environment but also for your and our health. Whilst the current wine trend is for fresh and crisp (more acidic) wines, its maybe not the best for your digestive system. High acidity also must be offset with residual- or added sugar for the wine to appear balanced, adding another culprit. Often seen in Riesling and Chenin Blanc, despite the high natural acidity in these wines. Maybe not a problem when you are young, but we want to enjoy wine for a long, long time…
In hotter climates or warmer years in cooler areas, grapes are already harvested with a low PH and malolactic conversion is deliberately suppressed to maintain the wine’s already low acidity (or may even have to be acidified).
Also, some grape varieties achieve naturally high sugar levels when physiological ripe but also contain lower acidity and a full malolactic conversion may make the wine ‘flabby’. Famous low-acid varieties are Viognier (also famously low-yielding) which pose challenges in keeping acidity levels while waiting for ripeness. Same for Gewürztraminer.
Depending on the season and consequent PH and TA of the grapes, we may let these wines through a partial malolactic fermentation or none, as we would never acidify our wines. (TA = total acidity, both fixed acids and volatile acids, present in grape juice or wine. With alcoholic strength and residual sugar, total acidity is one of the most common wine measurements involved in any wine analysis).
How to stop Malolactic conversion
Often large quantities of crisp white wines released soon after vintage are sterile filtered to stop malo and to make sure the conversion doesn’t happen later in the bottle. Cool temperature also stops the bacteria to work and of course Sulphur will eliminate the bacteria’s too.
Grape varieties and malo
Most of our wines go through long cool fermentation of several weeks, including a post-fermentation maceration of the reds, by controlling the temperature in the winery to stay under 15 degrees. At some stage, the wine will naturally progress to the malolactic conversion unless it is stopped with Sulphur.
Chardonnay and Sauvignon Blanc show always good acidity levels (low PH) and Hans lets them through full malolactic fermentation. That explains some of the softness, creaminess, and our wines. Of all the grape varieties we grow, Chardonnay is also the most difficult grape when it comes to malo and needs a lot of attention to make sure it goes through smoothly.
In which vessel does malolactic fermentation take place
As most of our wines go through malolactic fermentation it takes place in either in a 225 liter barrique, 500 liter puncheon or amphora where the wine will remain until bottling. At the same time, we stir the clean and healthy lees in the white wines for additional creaminess once a week. After fermentation, inclusive malolactic fermentation, the wine is racked (racking = removing clear wine from the settled sediment and rough lees at the bottom of the barrel) and the barrel cleaned of the rough lees. The wine is then transferred back in the same barrel and stays on its fine lees until bottling time.
Fermentation inclusive malolactic fermentation is from barrel to barrel different. For whites it is mostly about 3 months and for reds it can be up to 6 months also depending on the temperature in the cellar. Sometimes a barrel takes its time up to year. Its nature and it does not worry us, we give them all the time and let them slowly work away.