Yeast Whispering

A long time ago in a garage far, far away…. Well, just down the road in Pocklington… We began to culture an old English-style top-cropping ale yeast. In 2011 we were trying to solve the problem of making cask beer that cleared beautifully without recourse to animal-derived finings. At the time, and in our rural East Yorkshire location, drinkers lore stated that “if it ain’t bright, it ain’t right”. Happily, opinions on beer have matured somewhat since then.

The culture that we settled on, subsequently designated MCY115, has gone on to settle itself (or flocculate!) beautifully across our range of beers. Having our own house strain has a number of advantages. We understand its strengths and foibles, allowing us to predict its performance when we look to develop new recipes. We know how it responds to different circumstances, vessel geometries, ingredients and procedures. MCY115, for instance, likes an early extra squirt of O2 during fermentation when dealing with high-gravity beers. It likes to start a fermentation cool and then warm up. We also know exactly how the yeast presents at each phase of fermentation. It is the No.1 brewer at our place, bringing most of the magic to our beers.

Final beer clarity was the original goal. We have learned since to manipulate our yeast across those beer styles that do not need to be clear. We also prize the flavour profile that MCY115 provides our beers. Yeast contributes most of the aroma and flavour to beer after all. Yeast selection largely determines what contribution other key ingredients make. Different fermentations with the exact same ingredients can yield hugely different results. Properties of yeast fermentations are all key elements in the final character of a beer. CO2 and ethanol are the obvious products of yeast activity, alongside esters, aldehydes, fusel alcohols, mouthfeel components and other compounds.

The husbandry of our house yeast is one of the most important jobs at Brass Castle. We must keep it viable and vital. As a microbrewery, we also bring in a host of other dry and wet yeasts to keep it company and produce the other styles that we make. But MCY115 does most of the heavy lifting. In fact, we’ve also been really pleased with the way it performs in our Disruptor NEIPA. That may seem surprising for an old English strain. However, there is really only one non-old-English ingredient element to the New England IPA style: aromatic hops. MCY115 brings some caramel/crystal flavours through to the finished beer in a profile akin to true contemporary NEIPAs.

Top-cropping of yeast is a very British process. It is an extremely effective way of maintaining the most viable and vital pitches of yeast for the next beer. The advent of cylindro-conical fermenters has led many brewers to bottom-crop, if they crop and maintain a yeast culture at all. Cylindro-conical fermenters are relatively cheap in terms of the floor space that they up but they are not ideal for yeast health and yeast re-use. Open fermenters that allow top-cropping are also more susceptible to contamination if not used correctly. While we’re very proud to husband our own house yeast strain in a traditional way, we are also conscious of the responsibility that we have to maintain the strain in the best possible shape. It has not let us down so far!

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