By Kieran Haslett-Moore
The first potential evidence we have of brewing comes from a cave in Northern Isreal showing a 13,000-year-old malting mortar. Any beer brewed in that stone age brewery would have been fermented with all the microbes the cave had to offer. The story of beer production since then has been one of refinement and yeast strain isolation. We have gone from fermentation by the many to in most cases fermentation by a single strain and just maybe we have lost out along the way.
Today I am not writing about mixed fermentation beers, that is beer brewed with saccharomyces yeast and bacteria and/or non-saccharomyces yeasts. That is undoubtably part of the same story but also one that is more ‘in vogue’ and covered elsewhere. I will instead focus on multi-strain saccharomyces fermentation and what you might be missing out on by using a single yeast strain.
If we are looking at the history of beer being 13,000 years old, single strain fermentation is a blindingly modern invention, barely older than hop stands, lactose enrichment, thiol manipulation and cryogenic hops. Until recently all brewers brewed with mixed strains. Looking at Europe and Britain, you can still see some examples although for the most part strains have been isolated and simplified using lab-based methodology. Brewers like Harveys in Sussex and Adnams in Southwold still use multi-strain yeast cultures. They are, however, very much the minority. In the case of Adnams the yeast has been reduced to two strains after originally being much broader. The two remaining strains do two quite different things and together they make Adnams beer what it is. While one of the strains is responsible for the ester and light phenol character (think prunes and sultanas with a pinch of cinnamon powder) the other yeast is responsible for attenuation. Take away one and the flavour profile of the beers changes beyond recognition, take away the other and you are left with under attenuated beer. In Adnams case they have the two strains banked separately and they re-culture the two at times to start over. Harveys on the other hand just re-pitch and have been doing so since the 1950’s. The two main saccharomyces strains in their culture have developed separately over that time and combine for clove like character that today would be more associated across the channel in Belgium.
What’s wrong with a single strain?
Ok, I can feel the homebrewers out there wrinkling their brows and wondering why the hell they need to look at more than one strain of yeast. If you are brewing West Coast IPA’s and NZ Pilsners, it’s true that perhaps you don’t. However, for more yeast driven styles there is a lot to be said for multi strain fermentation.
When I started home brewing the range of yeasts available to us was a lot more limited than it is today. Debates raged on the Yahoo Mail lists about the two Saf yeasts that were widely available. Today we have a broad range of yeast strains available to us, we have good information about where they came from, and we even have genetic testing showing which strains under different labels and from different labs are the same. We even have an NZ based yeast lab.
So, brewers can buy a strain from a particular classic brewery, plop it into their own set up and expect to get a similar result. However, that seldom happens. These strains that have developed in the specific environment of the source brewery, in specific shaped fermenters, with specific environmental and process derived parameters often don’t behave the same or even well in a homebrewer’s set up. These rehomed strains can sometimes not attenuate, throw out harsh esters, refuse to flocculate, generally throw a sulk. There are of course a multitude of potential causes and solutions to any of these problems but one which is seldom utilised but often effective is to look to recent history and use multi-strain fermentation. By co-fermenting with multiple yeast strains you can literally fill in the gaps. A classic example would be the Dupont derived saison strains which are notorious for “stalling” that is to say the yeast finishes early and then waits for the diastaticus glucoamylase enzymes to break down the remaining dextrins so it can complete fermentation. However, fermenting with 2 or 3 saison strains, or even a saison strain plus a different Belgian strain, at once removes this stall and has the happy side effect of giving your beer a less standard ester profile.
How to make history repeat?
One of the potential problems with multi-strain ferments is the yeast blend will change rapidly over the generations if you re-pitch it. The strains settle into more and less dominant parts of the mix. I talked to a room of homebrewers recently about this technique and they were horrified at the unpredictability of it. However, in practise the changes are seldom massive, and in my experience never detrimental to the beer. As homebrewer’s you are not tied to strict brand profiles so some variation as long as it isn’t in a negative direction is part of the joy of brewing. If that is leaving too much to chance, then blending strains to a general ratio and only going one generation is always an option. This can be as simple as taking 2 sachets of different strains, pitching them together 50/50 or making a starter with one and dry pitching the other to give one an edge. Or it could be a full on as breaking out the microscope and doing cell counts on various starters and pitching amounts of each yeast accordingly. Be the master of your own journey.
As it isn’t my area of interest I haven’t tried but I am sure there is some scope for using multi-strain ferments with hazy pale ale and IPA beers to create interesting and different ester profiles.
Happy Brewing into the unknown multi-strain future!