Double yeast pitching – the new trend?

Yes, you read that right: double yeast pitching. Never heard of that? Never mind, neither have I – until recently. Then I started some research, talked to one of my colleagues in Freising (who is quite a yeast-afficionado) and put together some basics for you.

Innumerable yeast strains, aromas and co.

The basic principle is rather simple and similar to the idea of dry-hopping: adding another yeast strain after primary fermentation is designed to add an aroma to beers. There are lots of different yeasts tasked with pepping up the beers involved. First of all, a distinction has to be drawn between top- and bottom-fermenting yeasts. Moreover, yeasts form different aromas. The total number of different yeast strains is estimated at 750,000, though of these only about 1,500 are known and merely a few hundred are used on an industrial scale. And which of them are suitable for double yeast pitching?

This depends on what aroma you are aiming to produce. The salient consideration here, however, is not only the choice of a yeast culture. There are also other factors influencing the formation of aromas. It is contingent, for example, on how much glucose is present or how the yeast is aerated and grown. So it’s difficult to say that you need one particular yeast strain to produce a particular aroma. As you can see, there are no precise operating instructions here.

At least we can start by stating that, to put it simplistically, in double yeast pitching one yeast is used for primary fermentation, and a different one for post-fermentation. But merely adding yeast to the finished product will in most cases not suffice, since yeasts very much resemble each other. Every yeast absorbs sugar, and uses it to form metabolic products. After this, hardly any sugar remains. So when following this process a second yeast is added, the yeast strain involved will lack the sugar needed for forming a further aroma. Thus after primary fermentation, it’s necessary to add more sugar, in what is called the make-up liquid. The second yeast culture can then create different aromas from the carbohydrates added (= sugar), and absorb some aromatics from the first yeast, thus enabling new aromatics to be formed, and specialty beers with a unique taste to be produced.

Reproducibility

Nonetheless, double yeast pitching also entails disadvantages. First of all, re-use is technologically complex, since now a mixture of two different yeasts is involved. It’s difficult to say what percentage of which yeast is contained in the mixture, since one of the two yeast strains will always have the upper hand and come out on top. Since most breweries have very stringent rules in regard to the purity of their yeast cultures, this constitutes a problem.
Reproducibility, however, generally proves to be difficult, since yeast strains are living organisms, which react differently. It is rarely possible to reproduce the same beer twice. However, to meet their customers’ expectations, breweries are required to produce the same taste again and again. Because once they’ve found a beer they like, people want to be certain that the next time they buy it they can look forward to the same taste once more.

With pure cultures, meaning the use of solely one yeast, this is much easier, enabling uniform products to be created, that always taste the same, making for satisfied customers. This is why beers have been brewed this way for the past 150 years. We owe this to Louis Pasteur, who in the 19^th century discovered that yeasts are micro-organisms. Shortly afterwards, out of the undefined mixtures used hitherto, individual strains were selectively isolated and cultivated, enabling the purity of the beer and a uniform taste to be guaranteed, making for assured reproducibility.

For this reason, double yeast pitching is as yet not being widely used, since brewers want to offer their customers a beer that always tastes reassuringly the same. So the risk of disappointing their customers is too great for breweries. But hobby brewers, in particular, have abundant scope for experimentation here.

Double yeast pitching is most definitely an interesting option! Are there any hobby brewers among you who’ve done some experimenting in this regard? I’m looking forward to hearing about it in the comments.

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