Berliner weisse, gose, sour ale. A beloved child has many names, but what's the difference, and how do you brew these types of beer?
Different types of sour beer
When we talk about sour beer, there are mainly two different types. One is the classic and more complex Belgian varieties made with Brett (wild yeast) and bacteria like gueuze, lambic, and Flemish red and brown. These require a completely different process and are a topic that deserves its own article.
What we are talking about here is kettle sour beer, and primarily the German styles berliner weisse and gose. Although these beer styles are "by the book" meant to be kettle-soured, that doesn't mean you can't experiment with kettle-souring other styles. It's entirely up to you!
Traditionally, these styles are soured with lactic acid bacteria directly in the fermenter. Many believe this is the only "correct" way to sour, but kettle souring is a faster and safer method. With kettle souring, the heat from the boiling process will kill the lactic acid bacteria, and there is no risk of it "contaminating" other equipment. This way, you avoid the risk of your next beer also turning sour.
Berliner Weisse
Most people are probably familiar with weissbier. That velvety German beer style made with large amounts of wheat, and tasting like a well-ripened banana. Add "berliner" in front of the name, and suddenly we have a completely different style.
Berliner weisse, like a regular wheat beer, should be brewed with a large proportion of wheat, but it should also have a lightly to intensely sour taste that comes from lactic acid bacteria. Traditionally, this should have a low alcohol percentage of around 2.5-3.5%, and when served, it was common to add fruit juice or syrup directly to the glass.
Although the complexity is not on par with the classic Belgian varieties, a berliner weisse can be very refreshing and good if the balance and acidity are correct.
Gose
Gose is in many ways similar to berliner weisse. Gose can have a slightly higher alcohol content (4-5%) than berliner weisse, but the biggest difference lies in the addition of salt and coriander. Here we get a good amount of acidity and fruity flavors, which, in combination with salt, makes for a very good sour beer. This beer is very popular in combination with fruit.
Malt
Traditionally, a true berliner weisse or gose should have at least 50% wheat, but of course, how you do it is entirely up to you. If you want to kettle sour a pilsner or an IPA, there's nothing stopping you, and the process is the same. A good standard base is 50% pilsner or pale, 40% wheat, and 10% flaked wheat, oats, or barley.
Hops
A kettle-soured beer should not be intensely bitter. Bitterness and acidity are not always good friends, so it's definitely worth keeping in mind. It's also not recommended to add any hops during the souring process. Hops are naturally antiseptic and will slow down the souring process.
Feel free to choose a simple German hop like Strisselspalt, Tettnang, Hersbrucker, or other low alpha acid hops. Use enough hops at 60 minutes boil to achieve 5-10 IBU. Beyond that, there's no need for more, unless you want to brew a Sour IPA or experiment, for example.
Yeast
The choice of yeast is not the most crucial factor in a kettle-soured beer. We can recommend either a clean yeast strain like WLP001, US-05, or S-04. If you want a bit more character in your beer, wit yeasts like WLP400 or M21 can give good results.
Adding lactic acid bacteria
To sour your beer, you need lactic acid bacteria. There are several alternative methods for souring. One example is probiotic stomach tablets, which can often be expensive. Biola will also sour your beer, but experience shows that over time it can impart a cheese-like flavor to your beer, which in most cases is not very pleasant.
Traditionally, a handful of crushed malt was used because it contains natural lactic acid bacteria, but here one should delve a bit more into the process to avoid other microorganisms that have no business in your wort.
For maximum control and ease, we recommend Lallemand's Sour Pitch, or Helveticus Pitch. These are blends of lactic acid bacteria specifically designed for kettle souring. They are formulated to give you maximum control over the process, fast results, and clean flavors.
It can also be beneficial to pre-acidify the wort with lactic acid (lactol). This means adding lactic acid to a pH of around 4.5 before adding lactic acid bacteria. This provides a good starting environment for the lactic acid bacteria and helps maintain head retention in the finished beer.
Equipment and temperature control
You don't really need a lot of extra equipment for kettle souring beer, but it's important to have good temperature control. It doesn't take many degrees over 40 for lactic acid bacteria to die. You also need a lid for your kettle/brew machine, or plastic wrap to cover it. A pH meter is also an advantage, both for pre-acidification and for checking the pH value during the souring process. If you need a pH meter, you can find it in our selection of measuring equipment.
Brewing kettle-soured beer
Brewing your own sour beer isn't difficult, but it's important to understand the process to achieve the right balance. This technique divides your brew day into two, so this is something you can brew if you're a bit short on time one day. Souring takes time, but isn't a lot of work.
- Mash and sparge as usual.
- You shouldn't boil your beer yet, but it can be a good idea to heat it to 90 degrees to pasteurize, or give it a quick boil to remove any bacteria that could cause unpleasant flavors.
- Cool the wort to 35-40 degrees.
- Measure the pH value, and add lactol (lactic acid) until you have a pH of around 4.5. Be careful, a very small amount can make a big difference. Use the pH meter frequently!
- Now add your lactic acid bacteria.
- Cover the kettle. If you have a tight lid, this is ideal. Otherwise, use plastic wrap to avoid air. Lactic acid bacteria are anaerobic, meaning they work best without oxygen. If too much air gets in, there's a risk of introducing flavors you don't want in your beer. If you want to be completely sure, you can flush with CO2 before covering with plastic wrap.
- Maintain the temperature of the kettle/brew machine between 35 and 40 degrees and let it sit. There's no fixed rule for how long this should take. It depends on the bacteria you've used, how much you've used, temperature, and perhaps most importantly: how sour you want your beer to be. Usually, 24 hours is enough, but some prefer to go longer. It's up to you. Do a quick check with a pH meter along the way, or taste it. Remember that the pH value will drop a little further after boiling and during fermentation. It's better to stop the process a little early than too late.
- Once you've achieved your desired acidity, you can boil, cool, and ferment as usual. After the boil, there are no lactic acid bacteria left in the wort, and you can treat it as you wish.
Philly Sour as an alternative
Philly Sour is a very special yeast that both sours and ferments your beer in a single fermentation step in the fermenter. After use, you can wash your fermenter as normal and reuse it, with no risk of your next brew turning sour.
The only negative thing one can say about Philly is that you don't have as much control over how much acidity is produced, unlike kettle souring where you stop the souring process exactly when you want.
Fruit additions
A pure berliner weisse or gose (or other sour styles) can be refreshing and delicious on its own, but this is one of the most popular styles for fruit additions. To get as much flavor as possible from these, we recommend adding fruit to the fermenter, preferably after primary fermentation. Fruit contains a good amount of sugar that the yeast will consume, so you will often find that there is more activity in the fermenter after fruit addition.
Be aware that it has fermented properly before bottling or kegging beer with fruit. Let it sit a few days longer than usual to be sure, and take hydrometer readings along the way. If you are adding fruit with a lot of acidity, such as raspberries, you should also consider stopping the kettle souring process a little earlier so that it doesn't become too sour in the end.
Remember that fresh fruit can often contain wild yeast and other microorganisms. Therefore, it is recommended to heat-treat it before adding. Boiling will often change the taste of fruit, but heating to around 85 degrees for a few minutes will take care of most of it. Freezing will not kill all microorganisms, but it will still break down the cell walls in fruit, so that the juice and flavors will be released more easily.
The easiest way is to add one of our fruit purees. These are pre-cleaned, mashed, and pasteurized, so you can add them directly to the fermenter after primary fermentation.
How much fruit puree you should add depends entirely on what you like and what characteristics you want the beer to have. But to get some effect from the fruit, we recommend a minimum of 2-3kg for a normal 25L batch.
