Guide to Kveik and Other Farmhouse Yeast: Fermentation

Kveik and other traditional northern European farmhouse beer yeasts are becoming rock stars of beer fermentation. They ferment mind-blowingly well and create exciting flavors for those who know how to use them. The guide you are reading gives this practical know-how. This second episode continues from the Introduction that provided background information. The next episode will teach you how to harvest and maintain farmhouse yeast cultures. Finally, Farmhouse Yeast Descriptions lists my experieces with various yeasts. Whether you brewing traditional or modern beer, this guide helps you to brew it better.

In this guide, I’m conveying two different brewing cultures in parallel. First, I’m describing how traditional farmhouse beers are fermented. Then, I’m telling how to use farmhouse yeasts as a tool for creating something new or just because of their outstanding performance. I firmly believe that this tool works best when you know its farmhouse origins, whatever your goals are.

I’m certainly not the first to write a farmhouse yeast guide. Lars Marius Garshol’s book Historical Brewing Techniques is the principal work on farmhouse brewing and his How to use kveik is an excellent online source.Escarpment Labs’ Using Norwegian Kveik: Old Yeast, New Tricks gives excellent tips too.

However, I believe that my long hands-on experience in brewing both traditional and modern beers brings in a new perspective. I have brewed with Nordic and Baltic farmhouse yeasts since 2015 and met many Norwegian farmhouse brewers. My experience comes from both original farmhouse yeast cultures and commercial versions isolated from them. The recommendations in this guide are largely based on my own experience. This is ongoing research and I will update this guide as we learn more.

For more information on farmhouse brewing traditions, please check my book Viking Age Brew. If you want see farmhouse recipes online, see my stories Sahti Recipe and Farmhouse Brewing Tips and Brewing Norwegian Farmhouse Ale in Hornindal.

Fermenters

Traditional brewers typically ferment in a tub covered with a cloth or a loosely fitted lid. Then, right after fermentation they rack or scoop the beer into storage containers. The beer doesn’t have time to grow stale and with highly flocculent farmhouse yeasts most yeast is left behind.

This works very well, but I like the convenience of modern fermenters. Usually, I start with a loosely covered fermenter and then close the lid and attach an airlock when the fermentation is calming down. This allows me to keep the beer in the fermenter longer without worrying about oxygen pick-up. When harvesting yeast from the top, I prefer bucket-shaped fermenters.

Some people think that they’ll need a heating system for hot farmhouse fermentations. Usually, hot fermentations can be done in ambient temperatures. Just cool the wort to fermentation temperature and pitch yeast. The fermentation should start soon producing enough heat to keep the temperature high. When fermentation is finishing, the heat production decreases and the temperature drops slowly. Wrapping some insulation around the fermenter helps too when the temperature difference between fermenter and the ambient is large. With small test batches heating might be needed.

The Amount of Yeast

Pitch rate (the amount of yeast pitched) can have a major impact on beer flavor and yeast performance. Modern brewers often vary the pitch rate according to the strength of beer but it is rarely tuned for each yeast or beer (though ales and lagers are treated differently).

The world of farmhouse brewing is very different in this respect. Pitch rates vary a lot from brewer to brewer, or perhaps from yeast to yeast. The rates range from extremely low to today’s norm. Nevertheless, also farmhouse brewers pay attention to this parameter and for their house beer, they keep the rate constant to get consistent fermentation.

With farmhouse yeast, you should see the pitch rate as an important parameter that needs not follow modern guidelines, though today’s rates are a good reference point. If your yeast and beer that you are brewing vary, then also your rates can vary, even from low to high.

In Norway, many farmhouse brewers pitch shockingly small amounts of yeast. When a Norwegian farmhouse brewer sent me yeast, he gave me this rule: one gram of dried kveik for 25 liters. Garshol’s How to brew with kveik gives a rule for farmhouse yeast slurry: one teaspoon of slurry for 25 liters. These are less than one-tenth of today’s rate, and often these rules are applied regardless of gravity also for strong beers.

Using a small amount of yeast seems to be an old farmhouse tradition, but the pitch rates of the past are unclear. Perhaps kveik has become so hardy because it had to multiply quickly and seize the wort extremely fast.

Today the reasoning behind small pitches is that kveiks produce more desirable flavors when pitched low. I have tested several original cultures of kveiks with a rate of 1 gram for 20 liters of raw ale, and for most of them, this has worked well: fast fermentation without off-flavors. It does bring out strong flavors from some kveiks.

However, I have also found that for some kveiks tiny pitches have resulted in slow starts and inferior flavor. Some of my strong sahtis have had sharp alcohol sting, although kveiks are known for their off-flavorless fermentation.

Escarpment Labs did a series of experiments and reported them in an article The impact of pitch rate on kveik ferments. They pitched 10 %, 70 %, and 100 % of the typical today’s rate. The message of this article that when pitching rate decreases, the flavor intensity of some kveiks increases but there’s no clear trend for all kveiks. The experiment also shows clearly that a lower pitch of kveik doesn’t lead to a faster and more vigorous fermentation, contrary to what some kveik advocates claim. There’s no one-size-fits-all rule for all kveiks but the article notes that a good sweet spot of kveik pitching rate might be somewhere between 10 to 70 %.

I agree with this 10-70 % range, although the experiment was made with only one kind of beer. I believe the beer type makes a difference too, or at least we should make a distinction between raw ales and boiled-wort beers. Raw ales are rich in nutrients and can probably handle lower rates, though nutrients can be also added to the wort (more about this in section Yeast Nutrients).

There’s little information on pitch rates of Baltic and Russian farmhouse brewers. When I asked this from Lars Marius Garshol he forwarded the question to Lithuanian beer expert Simonas Gutautas who gave this example of a Lithuanian farmhouse brewer’s pitch: 0.75–1 liter of thick yeast slurry per 100–150 liters of beer. This is fairly close to today’s guidelines. I have tested two commercial Lithuanian yeasts, The Yeast Bay Simonaitis and Omega Yeast Jovaru with a 70 % pitch from the modern rate and that worked well. Before we learn more, I continue to pitch Lithuanian yeasts moderately low. The tiny kveik dosages might be too extreme for the Baltic yeasts.

Commercial yeast manufactures don’t want to recommend tiny pitches for their kveiks because that might result in failure. Some manufacturers don’t want to give any recommendations that deviate from their guidelines for brewer’s yeast. This is problematic because with some kveiks normal modern pitch rate can produce a disappointingly normal flavor. In my opinion, you can experiment with a wide range of rates also with commercial farmhouse yeasts.

With kveik fermented raw ales, I have now settled on a 1–2 grams of dried kveik or 1-2 teaspoons of slurry for ten liters. For boiled-wort beers, I usually pitch 50–70 % of the typical modern rate. I feel that these rates ensure good fermentation and give good flavors. For malt-forward beers, both raw and boiled-wort, I often pitch “even more” to soften flavors. These are not cast-iron rules and likely they’ll change as I experiment more.

If you are confused and don’t know what to do, this rule will work reasonably well: check the modern pitching rate and take 50–70 % from that. I do think that lower pitching rates are part of the farmhouse culture. My experiences with various yeasts and pitch rates are fully documented in Farmhouse Yeast Descriptions.

Fermentation Temperature

The ability to ferment well at high temperatures one of the fascinating traits of Farmhouse yeasts. If you are brewing a traditional farmhouse ale, it is best to start with the fermentation temperature that the original yeast owner uses. 

Although the farmhouse yeasts have been trained to work warm, many of them work well over a surprisingly wide temperature range. This can be used in the search of new flavors and a perfect pint. Generally, the fruity or spicy fermentation flavors increase with temperature but this is very yeast dependent. For some yeasts, the increase is dramatic while for some yeasts the fermentation flavors are relatively similar across a wide range of temperatures.

As an example, I have used Sigmund’s kveik at 18–40°C (64–104°F), and every time it has fermented well to a finish. At 20–25℃ (68–77°F) this yeast has given mild fruitiness somewhat similar to English strains. Above 25℃ (77°F) the fermentation flavors get stronger but do not rise steeply. Sigmund Gjernes himself ferments around 40℃. In my opinion, with this kveik the pitch rate plays a bigger role in flavor intensity. 

Yeast Starter 

Farmhouse brewers usually pull out a small amount of the first wort, cool it to fermentation temperature, and add yeast to it. This is the yeast starter that activates the yeast. Farmhouse brewers often lauter slowly which gives the yeast two or three hours to wake up, even without the wort boil. 

If your lautering to pitch takes less than two hours, it is better to make a starter earlier during the brew day. Normally I make a starter from dry malt extract 2–4 hours before pitching. A small low gravity starter is enough, such as 1/3 liters of 1.040 gravity wort for a 20-liter batch. 

With fresh commercial liquid yeast you don’t need a starter, and with commercial dry yeast, such as LalBrew Voss Kveik, hydrating the yeast in water is enough. 

Yeast Nutrients

Escarpment Labs have found that kveiks require more nutrients than typical brewer’s yeast, see Crispy brewing with kveik: mind the pH gap. This is natural because farmhouse yeasts have been used to nutrient-rich high gravity worts. Furthermore, low pitch rates can increase the need for nutrients.

Some brewers have noticed that kveiks do not always ferment well low gravity worts. This has been attributed to low amounts of a nutrient called free amino nitrogen (FAN). Richard Preiss of Escarpment Labs recommends supplementing the wort with yeast nutrients containing FAN when the original gravity is below 1.060. 

When I’m brewing boiled-wort beer, I always add yeast nutrient. Raw ales are naturally rich in nutrients and when brewing them I usually don’t add nutrients. 

Any nutrient blend containing nitrogen, such as White Labs or Wyeast yeast nutrient, should work. With all-malt worts, the nutrient manufacturer’s recommendation is probably enough. That’s what I’m doing with White Labs or Wyeast nutrient (the recommended dosage is 1/2 teaspoon for five gallons). I add half of the nutrient to the starter and the other half to the wort during the last ten minutes of the boil. 

I’m discussing nutrients for cider and mead making next.

Making Ciders and Meads with Kveik

Here’s my cider fermentation method with Sigmund’s kveik (original culture): I add a few flakes of dried kveik to unpasteurized apple juice that hasn’t been treated with sulfites. The cider ferments at 18–20℃ around 2-3 weeks. The gravity goes typically from 1.046 to 1.002. Then I cellar the cider at least for a week, rack to a keg, add sulfites and potassium sorbate, sweeten and force carbonate. 

Because I don’t kill apples own wild yeast, they might be fermenting the cider along with kveik but nice tropical fruit flavor suggests that kveik is doing a major share of the job. I used to do this with dried wine yeast but now I like the flavor better with kveik. 

Apple juice is low in nutrients but some traditional cider makers believe that best ciders fermented slowly without additional nutrients. So far I haven’t added any nutrients to my ciders and they have fermented well every time. Perhaps I’ll experiment with nutrient additions next apple season. 

I haven’t yet made mead with kveik but I’m sure that Sigmund’s kveik (and all commercial Voss kveiks) for example, will make a great mead. Meads definitely benefit from nutrients that provide plenty of FAN, such as DAP or Fermaid K.

Kveik and pH

Escarpment Labs have also reported that during fermentation kveiks drop pH more than brewer’s yeasts typically do, see Crispy brewing with kveik: mind the pH gap. 

Low beer pH may render the beer thinner and one dimensional in flavor. This can be a problem in low to medium strength beers (ABV 5 % or less) or in stouts and porters that sometimes have an acidic taint even when fermented with brewer’s yeast. When fermenting boiled worts with kveik I just shoot a little higher wort pH. Rember that high pH during mash or boil can lead to other problems, such as leaching tannins from malt or coarse hop bitterness.  

Aeration

Modern brewers typically aerate their wort before fermentation, but traditional brewers rarely do this, apart from inadvertent splashing. When brewing raw ales, I usually don’t aerate the wort. If your raw ale finishes sweeter than you would like, consider adding a short aeration step next time. When brewing boiled-wort beers, I always aerate the wort similarly to modern beers.

Fermentation Time

Farmhouse brewers expect their yeast to start fast and that’s what kveik and Lithuanian yeasts generally do. At high farmhouse fermentation temperatures, I usually see at least hints of fermentation within six hours of pitching. If fermentation hasn’t started within the first 12 hours, that might indicate poor yeast health or too low pitch.

Some brewers have wondered why they don’t get fast fermentation with kveik. First of all, when people rave about fast kveik fermentation they can actually mean that the beer is almost fermented in 1–3 days, and then some extra days are needed to drop the few final gravity points. Furthermore, several things mentioned above can slow fermentation, such as low pitch rate, nutrient deficiency, and yeast rising to the top prematurely. 

In my experience, some commercial isolates are slower than the original cultures. For some commercial kveiks and Lithuanian farmhouse yeasts 3–5 days might be a more typical fermentation time. Nevertheless, original or commercial farmhouse yeast, I rarely have wait for more than five days. Because most farmhouse yeasts flocculate fast and you don’t need to wait for the off-flavors to dissipate, the beer should be ready soon even with “slower” fermentation.

Managing Fermentation

Traditional farmhouse fermentation typical is very short: ferment two to three days at warm and then cellar the ale. The reasons for the prompt chilling are:

• This is a traditional method to combat souring bacteria. Usually, the yeast is in charge during the active fermentation, but as soon as the yeast is finishing up, souring bacteria may take over. Chilling slows everything down and you can get nonsour beer with this method even when the yeast contains traces of souring bacteria.
• Chilling the ale when fermentation is finishing up can provide a desirable residual fermentation. This gives gentle natural carbonation, protects the ale from staling and active yeast keep bacteria at bay.
• Nordic and Baltic farmhouse ales often taste sweet, and ale that hasn’t fermented completely may actually taste better. This is especially true with raw ales.

If you are brewing a traditional farmhouse ale, you can follow this procedure:

• It is best to monitor the fermentation early on and often. The fermentation can be finished even within the first 24 hours.
• Once the fermentation seems to be slowing down, inspect the beer surface and taste the ale. Does it taste unfermented or dry enough? Remember that the ale becomes slightly sweeter once the yeast drops. Measuring gravity helps to judge the progress, although this isn’t farmhouse brewers typically do. But hey, they have brewed the same beer over and over again for years. 
• Some farmhouse yeasts raise to the top way before finishing their job. A thick yeast mat floats on the top and the beer might look relatively bright beneath. The fermentation slows down, but beer may be still too sweet for your palate. The original gravity may still be in the range of 1.030–1.040. In this case, stir the yeast back into suspension. Usually, the yeast raises top soon, and you repeat stirring a few times. 
• With traditional Nordic and Baltic farmhouse ales you don’t need to be absolutely certain that the beer has fermented completely but you definitely want to avoid unpredictable refermentation later on. You can go by taste and chill the ale once it tastes ready. Remember however that you need to be careful of overpressure if this ale is transported or stored at warm.
• If you are unsure of what to do or you need to store or transport beer at warm, wait an extra day or two. Then chill the ale. 
• If you cannot chill the fermenter that is still OK for a while if the yeast doesn’t contain bacteria. Just proceed soon to the next step.
• Once the most yeast has dropped, package the beer promptly. 

Perhaps these two examples will clarify things:

1. I wanted to mail my sahti as a Yule present. The fermentation with Sigmund’s kveik was very close to a Finish after three days but the airlock still bubbled slightly. Just in case, I continued warm fermentation for two extra days, and then chilled the beer. On day seven I bottled and mailed sahti to Scotland where it arrived six days later. I was relieved to hear that sahti arrived in good condition without overpressure in the bottle. 
2. My traditional sahti had fermented with Sigmund’s kveik for three days. It tasted right and the gravity was 1.034 as it should be. I cooled sahti although it might have fermented a few gravity points further. On day six I bottled. I knew that I and my friends will store it cool so that refermentation was not an issue. I would never mail this kind of sahti. 

If you are fermenting modern beer, I assume you want to complete fermentation without any worries about refermentation. Wait a bit longer but I don’t see a need to wait for weeks (see also my note on bottle conditioning below). 

If you want to be sure how far the beer will ferment, pull out a small sample and let it ferment all the way at warm. Let the beer sit several extra days at warm and shake the sample a few times to guarantee complete fermentation. If the yeast culture contains souring bacteria, this test can reveal (by tasting or measuring pH) that too. 

Remember that four gravity points is about the maximum refermentation in a glass bottle. For example, if the beer you bottled early had a gravity of 1.025, anything further than 1.021 would create a dangerous pressure. 

Flocculation

As far as I know, all kveiks flocculate (rise to the top or drop to the bottom) very fast after fermentation. Usually, my kveik fermented beers are bright from yeast in two days after finishing the fermentation. Perhaps the large temperature difference from taking the beer very warm fermentation to cellar temperature speeds up the process too. 

Most Lithuanian yeasts seem to be highly flocculant too, except Omega Yeast Jovaru. This is slower to flocculate but even that will drop bright relatively quickly once you cellar the ale. 

Packaging 

I’ll first explain why traditional ales cannot be always handled like today’s beer:

• If the ale was cooled before fermentation was completely finished, you need to make sure that it won’t referment unpredictably later on. If the ale is stored cool this is not a problem. Usually, the ale won’t referment much below 10℃ (50℉). A day or two at warm usually doesn’t wake the yeast, but whenever I give bottles to friends I warn them: do not store these at warm for a week.
• If you used farmhouse yeast that contains bacteria, it is best to store the ale cold at all times after the warm fermentation. Bottle conditioning is out of the question unless you are intentionally brewing sour beer.

In the old days, farmhouse ale was stored in a wooden cask in a cool place. The cask would allow some refermentation and the bung prevented bursting. Today plastic canisters, plastic soda bottles, and stainless steel kegs have largely replaced the farmhouse casks. They are easy to clean and allow easy checking and releasing of pressure. With farmhouse ales, it is completely normal to drink a portion of a bottle or canister and finish the rest in a few days. 

Plastic canisters and soda bottles aren’t pretty but they are very handy when the ale is served very fresh to a large group. Plastic allows some oxygen pick up but the ale doesn’t have time to grow stale at a party. 

I often use swing top glass bottles for traditional ales that might referment. Then I can easily check the pressure or drink the bottle halfway. For completely fermented beer, farmhouse yeast or not, I prefer kegs and crown-capped bottles.  

Carbonation

In Viking Age Brew I argued that in the past when farmhouse ale stored in a wooden cask, the first pours may well have been lively and foamy. As more ale was drawn, it became gradually more still, much like a cask-conditioned ale does. Therefore, in the past, nearly all kinds of carbonation levels were traditional, though a gentle real ale like carbonation was probably the most typical.  

Packaging Nordic or Baltic farmhouse ale as such, without priming sugar or force carbonation, would be the most traditional. However, I don’t mind if you bottle condition or force carbonate. Today many farmhouse brewers in Norway and Lithuania do it too. I have noticed that some people find low or non-carbonated beer odd.

Flavorwise, my preference is:

• High gravity raw farmhouse ales do not need much carbonation. Sahti tastes excellent even still.
• Smooth real ale like carbonation suits to well to most farmhouse ales. 
• Lower gravity farmhouse ales with lighter texture clearly benefit from carbonation.

Bottle conditioning with farmhouse yeast clean of bacteria works well. Kveiks flocculate so fast that it is best to bottle condition soon, in less than a week from finishing fermentation. Otherwise, you might need to add more yeast at bottling or wait for a long time for the beer to carbonate. When you bottle early, then also your beer conditions within a week. You don’t need to bottle condition at high fermentation temperature, room temperature is enough. 

When I’m bottle conditioning with kveik or Lithuanian yeasts, I typically bottle 3–7 days after the brew day (2–4 fermentation after has ceased). Usually the beer carbonates in 3–8 days. This tip from Randy Mosher’s Mastering Homebrew is really handy with farmhouse yeast: put one beer into a plastic soda bottle so that you can check the pressure by squeezing. 

The next part of this guide teaches how to harvest, reuse, and maintain a farmhouse yeast culture. The final part, Farmhouse Yeast Descriptions lists my experiences with various kveiks or Lithuanian yeasts. If you haven’t already read the part I Introduction of this guide, please check that for useful background information.

Update History:
May 24, 2020: Added section on wort aeration.
February 26, 2021: Shortened the story name (originally Practical Guide to Kveik and Other Farmhouse Yeast).