Finding a yeast that provides all of the characteristics you want, whilst achieving a high ABV can be a tricky job. This week we caught up with JK who shared a technique he uses to improve yeast performance when brewing big ABV beers, read about it below.
“One of the main problems that brewers face when brewing exceptionally big beers is yeast performance. High alcohol big beers are extremely stressful environments for yeast, not to mention actually toxic once the alcohol content becomes high enough.
There are yeast strains about that are engineered to deal with these highly stressful environments and have a high alcohol tolerance. But what if you enjoy the character from your own house yeast, or you have a favourite store bought strain that’s always served you well but it struggles in bigger beers?
I attended an interesting seminar on this subject not long ago. Kara Taylor from Whitelabs explained that “in 72 hours most flavour compounds are formed, adding yeast later than 72 hours is unlikely to add to the flavour and aroma of that beer”.
A famous San Diego brewery brews a beer with a starting gravity of 1.094, their house strain struggles to finish this beer and stresses about creating off flavours. They start the initial fermentation with their house strain but after 72 hours (approx 1.030) they repitch with WLP001 to finish the beer. Their house strain provides the malt balance they require while the WLP001 has a better alcohol tolerance and helps to finish the fermentation while alleviating stress.
When adding yeast at this point of the fermentation, there are little to no nutrients left in the beer, there’s no oxygen and there’s alcohol of a percentage that may be toxic to some strains – strain selection is therefore very important.
To test this theory I created an imperial stout wort with a starting gravity of 1.103 I then pitched my favoured dried yeast, Mangrove Jack’s Burton Union M79 (usual attenuation of 77% and an alcohol tolerance of 9%) at a pitching rate of 1 million cells per millilitre of wort per degree of Plato.
Realistically I was hoping for it to get to 1.040 and then repitch, but it surprised me by stopping at 1030.8. At this point the beer was at 9.7% with little to no nutrients left so I repitched with Mangrove Jack’s US West Coast M44, an alcohol tolerant strain with its glycogen stores full and nutrient levels high. Within a few hours this had started fermenting again and had dropped to 1.027.
At the end of fermentation the beer ended up at 1.025 and a very healthy 10.4% ABV. At bottling time I reseeded the beer with a bottling yeast that performs well at high alcohol percentages just to make sure that there’s enough live yeast cells to carbonate the beer.
The beer itself is beautiful, no off flavours or aromas are evident, there’s no solvent like character or higher alcohols present, just a sexy imperial stout that’s an absolute beast.” – JK
Try it out yourself on your next big beer brew and let us know how you get on.