a particular strain of yeast, and saying “kveik yeast” is a bit tautological, although the term looks to cover a distinct family of yeasts. However, within that family are dozens, perhaps hundreds of different individual strains, and any one person’s kveik can contain between two and ten different individual strains. This use of multiple yeast strains appears to be important.
Some kveik are bottom-fermenting, some top-fermenting, and some intermediate, depending, basically, on where the brewer collected the yeast from at the end of fermentation. According to Lars Marius Garshol, who literally wrote the book on Norwegian farmhouse brewing, “in some areas, such as Sunnmøre and Nordfjord, there was a tradition that yeasts should be mixed every five years or so, and kveiks from those places show a much greater variety of yeast strains.”
Richard Preiss, co-founder of Escarpment Laboratories, based in Guelph, Ontario, whose company has done perhaps the most research into kveik of any on the planet, has suggested that these different strains need each other, that one makes a vitamin that the other ones need, and vice versa. According to Garshol, Preiss “always seems to get slower fermentations with single-strain yeasts from kveik cultures than [we see from others] with the mixed cultures. So they can survive without each other, but fermentation goes faster and easier with the help of the others. But doing an experiment to prove or disprove that in a way that’s reproducible by others is very difficult.”
That is not the most interesting fact about kveik, however. The aspect of kveik brewing that is most likely to ensure its adoption outside Norway is the range of flavours it is possible to get from the yeast, fruity and deep, which chime with the search for more flavour that seems to power much of the innovation in craft brewing right now. But there are other wonders: the high temperature tolerance exhibited by kveik strains, for example, many of which are happy fermenting at up to 40ºC.
Preiss, a tall, bearded and friendly Canadian, speaking at the Norsk Kornøl Festival in Hornindal, Western Norway, last month, revealed that his company had tested 25 different strains from samples of kveik supplied by Garshol, “and all of the ones we tested grew at 40ºC, while two thirds of them were tolerant to 42ºC, which isn’t normal in the larger world of beer: most people are fermenting at 20. This is remarkable. There are prominent yeast scientists that have engineered yeasts to work at 42ºC, and here’s a whole bunch of natural ones from Norway that do it too.
“This means that a home brewer who doesn’t have a lot of equipment, they don’t have a fridge to control the temperature, if it‘s 30ºC in a small city apartment they can still make a clean beer in the summer, and that‘s a little bit revolutionary, because that wasn’t really possible without these yeasts.” There are also, Preiss says, “some real opportunities for using these yeasts elsewhere, such as the ability to make good flavours, good beer at high temperatures. It means that a craft brewery in a tropical climate can maybe reduce their cooling costs and make their beer more energy-efficient.”
How did kveik yeasts evolve to be happy at such high temperatures? Garshol suggests it was due to the pressures the farm brewers were under, which influenced the yeasts they chose to preserve for brewing the next batch of ale: “The fermentation temperatures are crazy. But when you look at the old sources, they say ‘milk-warmÆ pretty much everywhere, in other words around 37ºC. Why is this? Obviously brewers want to add the yeast as quickly as they can. But as the wort cools, it cools more and more slowly. And with old-fashioned cooling methods and 150 litres of wort, that was slow. So there are lots of accounts of brewers having to stay awake until the middle of the night before they can add the yeast. And of course, the longer you wait, the greater the chance that some lactic acid bacteria gets in there. So you really want to ferment warm – the warmer you could ferment, the better.” Those yea