The Dunning-kruger Diaries - What I Thought I Knew About MLF

Social psychologists David Dunning and Justin Kruger identified the Dunning-Kruger Effect in a 1999 study, which describes a cognitive bias where people with low ability in a task overestimate their competence. Otherwise put, the less you know, the more you think you know.

Ignorance – a bug in the system

I recently became aware of the Dunning-Kruger Effect when it was used to shed light on the rantings of a prominent global figure. And then, I begrudgingly realised that I too once fell victim to this effect. At the start of my rookie days, I was quickly put in place during a cellar technical visit by the veteran winemaker, the late Hermann Kirschbaum, when I gave my poorly informed opinion on malolactic fermentation (MLF). I’ve learned a great deal about this topic since that humbling experience, mostly from winemakers, and I hope this blog post on what some call ‘bugs’ will be useful.

The Big Five of MLF

Similar to the Big Five in Africa, we also have the Big Five of MLF. Broadly speaking, they will determine whether you’ll have a successful MLF or not. The table below gives an outline of what they are and when MLF could become challenging.

Remember, the inhibitory effects of the conditions above are cumulative. What does this mean? Well, the more these numbers are out of whack, the more you will struggle to get MLF done. As an extreme example, I got a phone call last year from a hobbyist winemaker who could not even get an MLF to start in a wine after numerous attempts with starter cultures from various suppliers. Analysis of his solitary barrel of Shiraz revealed an alcohol content of 16.5%, total SO₂ of 90 mg/L, and malic acid of 1 g/L. Assuming the wine temperature followed the same downward spiral as the rest of his analysis, the final nail in the coffin (or rather barrel) was a pH of 3.17. After explaining to him that he had a better chance of winning a trip to the moon than MLF completing, I audibly heard reality sinking in with his utterance of a word I cannot repeat here.

The citric solution to freshness

Commercial MLF starter cultures are an absolute treat. Apart from their primary job, which is the timely and complete conversion of malic acid to lactic acid, selected cultures also improve mouthfeel, aroma, colour, complexity and microbial stability.

And freshness.

Here’s how it works. As malic acid nears depletion at about 0.2 g/L, most O. oeni strains shift their attention to a new substrate, often citric acid. This metabolism produces several compounds, most notably diacetyl, the source of those buttery notes in some wines. By selecting an MLF strain with negligible citric acid metabolism, the citric acid – and the freshness it brings – remains intact. And this is how a bit of metabolic magic leads to a fresher wine.

The wild card of MLF

If you like gambling, then ‘playing the wild card’ will be a familiar concept. For those unfamiliar with it, it means introducing an unpredictable, unexpected, or unconventional element into a situation. Like spontaneous MLF. You see, letting MLF run wild is a great thing … until it isn’t.

Sure, it can elevate native nuances, highlight terroir, and it’s free. However, due to its unpredictability, there is also the risk of MLF not kicking off, stuck or sluggish MLF if it eventually does, and various types of spoilage, including mousiness. Furthermore, wild MLF also carries the risk of downstream processing issues, particularly with regard to filtration.

The bugs behind MLF may be minuscule, but their impact on wine style and quality is anything but. Underestimate them at your peril.

For more information, contact Bernard Mocke 

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