Today Finnish farmhouse ale sahti is invariably fermented with commercial baker’s yeast. Before store-bought yeast, sahti brewers had their own house yeast. Unfortunately, these traditional yeasts died out in the 20th century. Can traditional Norwegian and Baltic farmhouse yeasts be used as replacements for sahti yeasts of the past?
Commercial baker’s yeast became available in the late 19th century. Therefore, fermenting sahti with baker’s yeast has become a tradition in its own right. I do not wish brewers to abandon this tradition. I am only advocating other fascinating options for fermenting sahti.
We need to delve into the history of sahti before judging the authenticity of sahti yeast. The path involves many intriguing questions. What sahti house yeast was like? Was it similar or very different from baker’s yeast? Can we recreate historical sahti?
I have written two books about sahti, Viking Age Brew in English and Sahti – Elävä muinaisolut in Finnish. If you want to know more about sahti, these books are full of highly readable information. Lars Marius Garshol’s book Historical Brewing Techniques is the best source on how Nordic and Baltic farmhouse ales are related.
Brewing Nordic site is also filled with information about sahti and similar Nordic-Baltic farmhouse ales. Start reading from Sahti and Related Ancient Farmhouse Ales or Sahti ja sen sukulaisjuomat (in Finnish).
The reasoning behind this posting would not have been possible without the recent scientific analysis of farmhouse yeast. Lars Marius Garshol has summarized well the increased understanding, see for example his Larsblog posting What makes kveik a super-yeast.
In 2002 European Union granted sahti the Traditional Speciality Guaranteed (TSG) appellation. This specification regulates what can be sold as sahti within the European Union. Therefore, it does not directly concern homebrewers as such. Nevertheless, it is the foremost specification of what is authentic sahti, so homebrewers refer to it if the authenticity is questioned. The definition of sahti connected with the TSG appellation reads as:
Sahti is traditionally prepared from raw materials including, in addition to malted barley, other cereal malt and cereals (rye, barley, wheat and oats) and usually hops, fermented using baker’s yeast or harvested yeast.
Here harvested yeast refers to traditionally maintained house yeast harvested from a previous batch of sahti. The specification does not limit where sahti is made, only how it is produced. Many traditional farmhouse beers in the Nordic and Baltic countries would meet the requirements of the appellation although they aren’t called sahti.
So, there are two options for fermenting sahti: baker’s yeast and traditional farmhouse yeast. Finnish sahti devotees explicitly agree that modern brewer’s yeast is unauthentic for sahti.
In 2017 I followed Norwegian farmhouse brewers in Hornindal. They brewed a raw ale made from barley malt, juniper branches, a small amount of hops, and traditional house yeast, kveik.
The brewing process was very similar to sahti. If I brew the same kind of wort and ferment it with baker’s yeast that would be a traditional sahti, perhaps in the style of Joutsa.
Just like sahti, Hornindal farmhouse ale is brewed for fresh consumption, especially in feasts. The drinking customs of Finnish and Norwegian farmhouse ales are essentially the same. If you want to know more about this fascinating aspect of farmhouse culture, see the chapter Beer as Part of Farm Life in Garshol’s book Historical Brewing Techniques.
Hornindal farmhouse brewers have been harvesting and maintaining their family kveik of in the same way as Finnish sahti brewers used to culture their “harvested yeast”. Therefore, this Hornindal ale is in fact Norwegian sahti and traditionally handled kveik is authentic sahti yeast.
This kind of farmhouse brewing was born way before national borders. It used to be a common way of brewing throughout northern Europe. But it has survived only in a few isolated spots, like the countryside of Norway and Finland.
How Sahti Brewers Harvested House Yeast?
Although Finnish sahti house yeasts have died out, the traditional yeast harvesting and storing practices are well documented. For example, in a book Sahtikirja Leena Mikkanen from Nastola describes the house yeast harvest as:
“In the old days the surface foam was harvested from sahti. It was dried and stored wrapped in a cloth. Dried yeast was added to the next brew of sahti”
Sahti yeast was also stored as a slurry, as some Norwegian farmhouse brewers still do. Also in Sahtikirja Kaisu Kaskue from Lammi describes how sahti brewer Tilda Tanner handled her yeast:
“Sahti yeast was harvested from the bottom of the fermenter and put into a bottle. The bottle was stored in a well until the next brew.”
Unfortunately, Sahtikirja does not mention when these “old days” were, but it must have been 1900–1970.
In conclusion, sahti brewers usually cropped yeast either from the top of fermenting sahti or from the bottom of the fermenter. The fermenter was a wooden tub from which sahti transferred to a cask. Sometimes brewers cropped yeast from the cask. Yeast was usually dried onto something: pieces of wood, cloth, hop cones, or birch whisks. Sometimes oat flour was mixed into yeast and before it was dried.
Some of these techniques may be untypical for Norwegian kveik (such as mixing yeast with flour) but the typical kveik harvesting methods were certainly used in Finland.
How Sahti Brewers Fermented With House Yeast?
Matti Räsänen describes typical sahti fermentation practices in his PhD thesis on Finnish farmhouse brewing. In the past, house yeast was usually added when the wort was no warmer than the hand or fresh milk. Fermentation time was short but carefully controlled. Too long or fast warm fermentation could finish the beer dry and tart. Good sahti was heady, sweet, and not sour, just like today.
In the ethnographic surveys of the 20th century, some sahti brewers have preferred colder fermentation temperatures. I suspect that this reflects the transition to commercial baker’s yeasts and new types of dairy equipment of the twentieth century. Especially aluminum milk cans introduced in the early 20th century made cooling of sahti wort much easier.
Today sahti is rarely fermented above 25°C. Warmer than that, Finnish baker’s yeast would ferment explosively and produce too dry and tart sahti. Interestingly, in the 20th-century ethnographic texts, some brewers complain that bought yeast ferments too fast.
In conclusion, when sahti was still fermented with house yeast the fermentation was at least in most cases similar to kveik brewers.
What Flavors Finnish Farmhouse Yeast Produced?
In the ethnographic surveys, the flavor of sahti is described plainly with words good, sweet, malty, robust, heady. Fruits or spices were unknown beer descriptors. Thus, the old texts reveal little about fermentation flavors.
It seems that sweet maltiness was much appreciated. The tartness was clearly negative. Alcohol strength was appreciated, as it has been with all Nordic and Baltic feast farmhouse ales.
The fruitiness was probably a typical flavor because that is hard to avoid with lukewarm fermentations. Did house yeast produce spicy and phenolic flavors, like baker’s yeast today? I suspect so, although this cannot be deduced from old texts. The surviving Lithuanian and Russian farmhouse yeasts produce phenolic beer. Likely Finnish farmhouse yeast was similar to the surviving Baltic yeast. However, it is also possible that some Finnish yeasts were non-phenolic and similar to Norwegian kveik.
The Difference Between Baker’s Yeast and Harvested Yeast
Today most sahti brewers use Suomen Hiiva brand of fresh Finnish baker’s yeast. In the sahti circles this yeast is known for its robust fermentation and banana flavor.
Suomen Hiiva produces this compressed yeast from a single strain in a highly controlled manner. When the commercial baker’s yeast production started in the late 19th century, the yeasts were likely obtained from brewers, as Lars Marius Garshol argued in Does bread yeast exist?
Yearly production of Suomen Hiiva is millions of kilograms, enough to supply the whole of Finland. When producing millions of pounds, one cannot expect totally bacteria-free yeast. The company’s standard is one lactic bacterium to ten thousand yeast cells. The yeast is likely to pick up more of these bacteria in the grocery store, where it is sold paper-wrapped alongside dairy products. Indeed, with fresh Finnish baker’s yeast beer goes sour so predictably that some Finnish craft breweries use it for sour beers.
Before the 2010s, commercial baker’s yeast and traditional sahti yeast did not seem dramatically different. Today we know that difference is dramatic: recent microbiological studies have revealed that traditionally cultured farmhouse yeasts are typically mixtures of yeast strains. Sometimes the house culture contains lactic acid bacteria but often the yeasts have competed out souring bacteria. House yeasts flocculate fast and produce beer ready to drink very soon.
What About Commercial Kveik?
Above I have compared sahti house yeast to traditional home-cultured kveik. What if sahti wort is fermented with a commercial single strain kveik?
Isolating yeast strain in a laboratory is hardly a traditional farmhouse method. Therefore, saying that commercial isolated single-strain kveik is harvested sahti yeast would be a stretch. On the other hand, commercial baker’s yeast is a single-strain culture also.
I would draw the line between yeast culturing methods: traditional home-cultured farmhouse yeast makes authentic sahti while laboratory isolates of farmhouse yeast do not. That said, occasionally I like to ferment sahti wort with commercial kveiks. It makes an outstanding ale with more predictability. Even a commercial kveik is clearly different from brewer’s yeast, especially if used the traditional farmhouse way.
I propose that an ale fermented with a laboratory-treated kveik is called something else than sahti. I have been calling my sahti-like ales søhti when fermented with commercial kveik. Then I’m free to do also other deviations from sahti tradition, such as carbonating the ale with priming sugar.
Why Broadening Sahti Fermentation Is Important?
I can think of plenty of reasons to ferment sahti with kveik or Baltic farmhouse yeast:
- Traditional farmhouse yeasts would add diversity to sahti.
- Avoiding sour sahti is easier with kveik than with baker’s yeast.
- Kveik flocculates fast and the ale is ready to drink sooner than with baker’s yeast. Less beer will be lost to dregs.
- If you culture farmhouse yeast with traditional methods the yeast will adapt to your brewing. Gradually it becomes your house yeast different from the original. You’ll get a virtually endless source of yeast.
Many of these points would be going back to sahti traditions before commercial yeast. In the days of yore, yeast was borrowed from a neighbor if the house yeast went bad. Today, Norwegian, Lithuanian, and Latvian farmhouse brewers could be neighbors to Finnish sahti brewers.
Of course, there are risks too. You can lose a batch or even the whole yeast if it gets contaminated. That’s probably why sahti brewers shifted to commercial baker’s yeast. Keeping a house yeast is a skill that takes knowledge and practice to learn. You can start learning by reading my Guide to Kveik and Other Farmhouse Yeast.
Hardly any beer is brewed today exactly like hundreds of years ago. This applies to sahti and most other alive remnants of beer history. The words authentic and traditional are agreements of what elements of traditionality needs to be fulfilled to justify the use of these vague words.
Nevertheless, traditionally cultured kveik or Baltic farmhouse yeast is as authentic sahti yeast as it gets in the 2020s. These yeasts represent what sahti brewers used to have before baker’s yeast replaced house yeasts.
As far as I’m concerned, traditionally maintained kveik or Baltic farmhouse yeast complies with the TSG appellation of sahti whereas commercial farmhouse yeast treated with laboratory methods does not comply. However, I’m not sitting in the office where the compliance is judged.
Let me stress that TSG Appellations are applied to commercial products within the European Union. Nevertheless, In my mind, it is best to reserve the word sahti for beers that strive for the tradition.
 European Commission, Agriculture and Rural Development. TSG-appellation of Sahti, registered February 2002.
 Asplund, Ulla (editor). Sahtikirja. Lammi, Finland: Suomen Sahtiseura, 1990. This is a collection of stories obtained from traditional sahti brewers. Collected by Finnish Sahti Society and written in Finnish.
 Räsänen, Matti. Vom Halm zum Fass: Die Volkstümlichen alkoholarmen Getreideget- ränke in Finnland. PhD Thesis, Suomen Muinaismuistoyhdistys, 1975. An extensive thesis on Finnish farmhouse ales, written in German.
 Räsänen, Matti. Ohrasta olutta, rukiista ryypättävää: Mietojen kansanomaisten viljajuomien valmistus Suomessa. Jyväskylä, Finland: University of Jyväskylä, 1977. A book Written in Finnish based on Räsänen’s thesis.