This was an excellent and riveting seminar, especially for those who thought that malolactic bacteria was one of (in my case not very many!) areas of wine biochemistry where we know it all! So much learnt, and in a fascinating lively way.
The seminar was presented by:
And with the lively contributions of the wonderful Sibylle Krieger-Weber of Lallemand.
To summarise the event, the most significant thing that we learned was that the bacteria that provoke malolactic fermentation also do so many other things in wine. That controlling them, and the timing of the inoculation, can have myriad effects beyond the malic – lactic acid conversion with which we are all familiar.
This makes complete sense when one considers how much more yeast does than simply converting sugar to alcohol.
Lactic Acid Bacteria (LAB) contribute to taste and texture of all fermented foods, and can inhibit other spoilage bacteria. They can also subtly change the flavour of the wine by creating thiols/sulphides.
Unlike yeast however, there are fewer strains of bacteria to consider because as the pH of the must/wine changes, and the alcohol increases, fewer bacteria can survive the environment. The most prevalent bacteria is Oenococcus oeni, although there are others which achieve MLF, just ‘not necessarily in a good way’ according to Silvano.
Lallemand’s selections have been based on the known tolerance criteria:
- Acidity (tolerance pH 2.8 – 4.5)
- Alcohol (less than 16% abv)
- Temperature (can tolerate low temperatures)
- SO2 (< 50mg/L)
Within this, the bacteria are selected according to their production of Biogenic Amines (in addition to histamine, these include such delightful sounding substances as putrecine, cadavérine, and spermidine, so you don’t need to be a chemist to know they are not great news!), and other factors such as Copper Resistance. And, according to the sensorial profile, their ability to limit or influence Cinnamyl esterase negative, Citrate Uptake and Mousy and other taints. Further considerations are production feasibility (in freeze dried form), and extensive trials for validation.
One of the key learnings is that carefully selected bacteria will not produce acetic acid from hexoses. Many wine producers reject co-inoculation with fermentation yeast due to the risk of VA developing. Lallemand’s particular strain of O.oeni prevents that because it cannot convert sugar to acetic acid. This is critical because the time between the finish of the alcoholic fermentation and the beginning of the MLF conversion – “the lag time” – as Sam Harrop described it, is a critical stage for the wine, where the winemaker’s main assistant is Sulfur Dioxide to prevent the development of off-flavours, and especially Brettanomyces.
This is like some kind of magic bullet. If the correct bacteria, inoculated during or very soon after fermentation, can prevent Brettanomyces spoilage (due to competition for nutrients), then the winemaker will have no lag time (which often in some European regions extend to the spring after the vintage), and therefore a need for less SO2. It will also limit temperature control expenses (the wine needs to be kept warm for MLF to occur subsequently).
Sam pointed out that some people would ask “Why would you even consider this when Chitosan is so effective?”. But although Chitosan kills ‘brett’, it does not alter the phenols already created. The bacteria can also alter perception of fruitiness (both directions, but mainly increasing), and different oak compound aromas. Co-inoculation reduces acid-aldehydes, which subsequently combine with SO2, and therefore less SO2 will be needed.
Co-inoculation also increases competition for nutrients with the yeast, and certain yeasts under stress produce fatty acids which creates fruitier esters.
And all this before what malolactic bacteria – to the layman – actually DO! Butter and cream!
The production of Diacetyl as part of the conversion produces the well-known buttery flavours, but can additionally create vegetal notes, govern/limit oak integration, increase the pH and decrease fruity/floral notes. All of this can be controlled by selecting the right strain, and management. Some producers actively want butteriness, and some to avoid it. For example, low pH/temperature and longer ferments with limited lees time tend towards high diacetyl production all of which make it more difficult to limit in Champagne base wine fermentation (where doing so is more highly desired).
Lower diacetyl production also occurs when co-inoculated compared to part-way through and post-fermentation.
To demonstrate all this we had a tasting of three Chardonnays, three Pinot Noirs and two Malbecs which were completely equal in all respects other than the strain of bacteria employed and/or when they had been inoculated. The wines were very discernibly different. Not different enough to be considered a ‘killer of terroir’ (although you do wonder just how much that has previously been ascribed to the earth is actually due to the things that live in it), but markedly different. Even the tannins (or the perception thereof) were different in the two Malbecs.
More control cannot be considered a bad thing. Especially if it can limit the production of off flavours (or eliminate the need for other mechanisms to control them).
In addition to this fascinating lecture, open discussion, and illustrative tasting, we had the chance to assist, via a tasting, Ray O’Connor with his research project, with which Lallemand have been instrumental in their support.
A fascinating day. Many thanks to Lallemand and all the contributors.
Rod Smith MW