Kölsch yeast is often referred to as being hybrid: a top fermenting ale yeast that can be fermented at lower temperatures. Just like a lager.
Because of this interesting characteristic, brewers have adopted specific Kölsch fermentation profiles unique to the style.
In this post I’ll discuss two Kölsch fermentation profiles and how you can perfect them using testable hypotheses.
A classic Kölsch fermentation profile
The original method for fermenting Kölsch was in an open-topped wooden fermenter.
With the knowledge that lower fermentation temperatures led to a cleaner beer, Kölsch brewers attempted to ferment at low temperatures without stunting yeast activity (Warner 1998).
A typical, old-style fermentation profile consisted of two stages.
First, the brew would be left to ferment at a temperature of around 9c – 13c. At these temperatures, full attenuation would normally be reached within a week.
Second, the brewer would cold-age the brew in underground cellars, where it would sit at between 5c and 7c for a period of between 5 and 7 months (Warner 1998).
Indeed, these temperatures weren’t very easy to achieve without the use of refrigeration equipment. As such, Kölsch brewers used ice that they had harvested and stored in underground cellars (Warner 1998).
Although Kölsch brewers still ferment in open-topped fermentation vessels, their use has recently declined in favour of large, cylindroconical tanks.
A modern Kölsch fermentation profile
Nowadays, a similar two-stage approach is used; however, Kölsch brewers start off by fermenting at a slightly higher temperature of between 18c and 20c (Warner 1998).
Personally, I think that this temperature is too high, and suggest that you use a lower fermentation temperature of between 16c and 18c.
I normally ferment my Kölsch at around 16c with great results.
The duration of this stage will vary, and is based on factors such as yeast strain, pitch rate, health, fermentation temperature and so forth; however, full attenuation should be reached within about five to seven days.
To confirm whether full attenuation has been reached, simply take two gravity readings: one on day five and one on day seven. If the gravity hasn’t dropped during this period, you’ve reached full attenuation.
The brew is then cold-aged at a temperature of between -1 and 1c.
According to Warner, cold-aging typically lasts one to two weeks, but some breweries still age their Kölsch as long as six to eight weeks (Warner 1998).
Personally, I leave the brew to cold-age for about 4 weeks, and never drop the temperature below 1c.
Truth be told, I’ll often shorten this period a bit if I’m getting extra thirsty!
Developing your own fermentation profile
Hopefully, you’ll have noticed that there are two, key variables to consider: temperature and time.
And by changing these variables, you can develop your own unique Kölsch fermentation profile that suits your tastes.
But don’t just go ahead and randomly change ’em.
Use testable hypotheses as the basis for any changes
A testable hypothesis is an ‘educated guess’ that can be tested by changing a variable (for example, time) and recording the outcome.
By using testable hypothesis, you can easily evaluate minor changes to your Kölsch fermentation profile.
Here’s an example of how I use testable hypotheses:
1) Develop a testable hypothesis
I recently had the opportunity to sit down and taste my latest Kölsch. It was pretty good, but the mouthfeel was off; it wasn’t as clean as I would have liked.
I reviewed my fermentation notes, and recalled that I only cold-aged for 3 weeks. I usually cold-age for longer.
I then wrote down a testable hypothesis: mouthfeel poor because I didn’t cold-age for long enough.
2) Test it
The next time I brew, I can test this hypothesis by increasing cold-aging time.
If, as I suspect, the mouth-feel is improved, I can make sure that all my future brews undergo a similar cold-age schedule.
If no improvement is noted, then I will reconsider my brewing notes and develop a new testable hypothesis to work with.
Important note: if you take this approach, make sure to only change one variable at a time. If, for example, I was to cold-age for longer and modify the recipe, it would be difficult to ascertain whether any improvement were down to the recipe change, or the time change.
As such, it’s best to work with one variable at a time.
And remember, like recipe formulation, small changes can make a big differences to your Kölsch.
Start by making subtle adjustments, and move on from there.
I’ve had incredible success using this approach, and have used it since I started brewing Kölsch. It certainly helps to take some of the ‘guess-work’ out of the mix!
So, go ahead and give it a shot. Make sure to let me know how it goes.
Do you have any tips on developing Kölsch fermentation profiles? See you in the comments!
Warner, Eric. Kölsch: History, Brewing Techniques, Recipes. 1998. Print