What is it that ferments lambic?

As everyone knows, lambic is fermented by “wild yeast and bacteria”. But what does that actually mean? What yeast? And what bacteria? This is not an easy question to answer, but last year a study attempting to answer this was published. The results are interesting in several different ways, so let’s take a look.

Let’s consider what they’re doing first. A batch of lambic is fermented in a fairly big stack of wooden casks piled on top of one another. It stays there for one to three years. The task of the researchers was to say what microorganisms are in there. This is non-trivial when a thousandth of a liter can contain 10 million microorganisms, or even more, and these are unlikely to be evenly distributed in the fermenting beer. A further challenge is that, obviously, these critters are too small to be seen, except with a microscope, and too many to be counted.

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