What are sour beers, how to make them, and why to drink them?
“This beer is sour, it must be spoiled!” You’ve probably heard someone say these words, or you might have by yourselves run into a spoiled beer that has gone sour… However, a beer being sour is not always a sign of spoilage. If you want to know a bit more about sour beers and how they’re made, keep on reading.
First of all, let’s make one thing clear – there are 2 main types of sour beer: intentionally and accidentally sour beers (we only do the first type, we promise).
What we call accidentally sour beers are beers that were not planned to be such, and got sour as a result of contamination during the process, due to the lack of hygiene.
Beers tend to get sour as a result of spoilage more often in the summer, since “wild” yeasts and bacteria are more active at higher temperatures.
Additionally, beer spoils faster in warmer weather since most craft beers are non-filtered and non- pasteurized, so present live yeast cells, that we intentionally put there, are also bound to work and simply speed up the ageing of the product, leading to spoilage, and, of course, unintended sourness in some cases. Oxidation also happens faster in the heat, so you’d want to buy a beer that was properly transported and stored, but make sure you treat it well yourself as well.
So, as a general rule for craft beers: try to get it fresh, drink it fresh and store it cool if you keep it, and you wont get a spoiled sour beer.
Kettle sours and how to safely sour a beer
Sour beers have been a growing trend in the world and so in Croatia as well, resulting in breweries replying to the market demands by experimenting with new bacteria and yeast and providing the product.
Now that we’ve established that we are talking about the intentional sour beers, it’s fair to say that these also have their subcategories. On the domestic market, the most frequent souring technique used is kettle souring, and it goes like this:
we go through some usual steps of the brewing process such as mashing, sparging and lautering, bringing it to a boil, but only a short one, and then we subject the wort to the souring process.
To remove the risk of unwanted flavors and aromas we need to run CO2 through the wort and run out most of oxygen that is present. 36C-38C is pretty much the optimal temperature for most strains used in
brewing and it takes them about 24 h to do their job, which is lowering the pH somewhere between 3.2 and 3.6, also giving it a pleasant lactic/citric acid taste and smell.
At this point, we thank the bacteria for doing its service, but now it’s time to kill it, which we do by raising the temperature to a boil and keeping it there for about 15 minutes. This is done once we are happy with the achieved level of acidity, so we can stop the process, but it’s also a precaution for future brews, since we don’t want any accidental sours.
To be fair, the chances of lactobacillus contamination of the brewing equipment on the cold side of the process are rather minimal, since they’re not exactly too resistant – in fact wort with 20+ IBU kills, or at least inhibits, most lactic acid producing bacteria, but why to take the risk?
Beyond this point, we are back on the regular brewing track: cooling, pitching the yeast, fermentation and everything else (see more under beer production)
Historically, kettle sour beers were mostly made in Germany. The styles remaining to this day are Berliner Weisse and Gose.
Souring during fermentation
Technology has provided us with another technique of souring beers, by isolating strains of yeast that have the ability to produce lactic acid during their regular fermentation metabolism. The best known of these is the yeast known as Philly Sour (GMO also available: Sourvisiae).
This approach to souring is simpler, safer, and takes fewer steps. However, there are noticeable differences to kettle soured beers.
Philly sour makes things simpler, but also produces a simpler beer. The acidity produced is less pronounced and gets nice peachy esters.
In conclusion, this yeast is good for moderately sour, but decently fruity beers, which are in fact proper entry-level sours for newbies.
Barrel-aged sour beers – a world of more complex sourness
The next souring method, and probably our favorite one, is by throwing in a mix of bacteria and certain selected yeast strains with the aim of getting a more intense sourness and deeper complexity.
The origin of this idea is not so far in the past, it has to do with Belgian breweries aging their beers in wooden barrels, in cellars,
where the microflora, souring the beers, was present both in, and out of the barrels themselves. This didn’t, of course, occur exclusively in Belgium, but in the rest of Europe as well, and we can only wonder what the beers were like at that time – at least somewhat sour, for sure. What we do know is that the Belgians certainly embraced this ageing technique as their traditional, so even nowadays there are breweries, such as Cantillon and 3 Fonteinen, which do their beers only in the old ways.
Today, we have the benefit of starting such a souring procedure in a significantly more controlled environment, with selected strains of bacteria and yeast, and not hoping to have caught the good microorganisms from the air and let them multiply in our wort. We are talking about strains of Lactobacillus and Pediococusthat we utilize for the souring.
Unlike in kettle sours, where we kill the Lacto strain pitched when it does its job, here we let it stay in the wood and do its job in the long run.
But why would we even drink beers that contain bacteria in them?!? It’s sour, and it stayed there in some wooden barrel for who knows how long?
The answer is simple: we let it stay on the good stuff!
Lactobacillus and Pediococcus strains are present in probiotics, yogurt, kefir, etc., so we are talking about healthy and useful bacteria which help the microflora in our digestive system, and strengthen our immune system. Besides the bacteria, we utilize quite
interesting yeast – Brettanomyces.
It’s a category of yeast known for very adaptive strains, which tend not to be too picky about their environment and can survive rather harsh conditions. Brett is often considered to be a wild yeast, and many think it’s the first one to blame for the acidity in sour beers, but that’s not exactly correct.
Brett can, depending on strains, produce even acetic acid, but that also often takes more dissolved oxygen in the beer or wort.
Brett is, in fact, in charge of other things: fermenting more complex sugars (ones that regular brewing yeast strains can’t eat), producing phenols and esters that give complexity to the beer, and basically sweeping up after the souring bacteria, for which it’s actually very highly appreciated. In a textbook case, the bacteria in the wort simply produce mainly lactic acid, and maybe some ethanol and/or CO 2 , but in reality, there are many parallel side products in their metabolism in order to produce the above listed desirable ones. Sure, the side products are present in way lesser amounts, and sure, some of them are indeed nice, but some, like isovaleric and isobutyric acid, smell like feet/cheese/vomit and a little of them goes a long way. The beauty of many Brett strains is that they can actually consume those nasty side products and create other pleasant ones.
So, Brett, given enough time, cleans out unpleasant aromas and flavours, while producing esters smelling like pineapple, apples, pears, etc. Oh, and speaking of phenols production, this group of yeasts is definitely to blame, that being manifested as cloves, spicy, peppery and the “funky” aromas. Brett eats anything it runs into, whether good or bad, and only makes the best of it.
All this applies, of course, if we have the proper strains of Brettanomyces, since there are some not so nice, and even nasty ones.
Most wine producers consider Brett their biggest enemy, and many brewers producing only “clean” beers are agreeing on this, but when well planned and intended for a beer to be “contaminated” by such yeast and be sour in the end, it’s definitely a rather rewarding procedure.
Microorganisms don’t take all the credit here, as mentioned earlier. We do make this fermentation and aging in wooden barrels, so let’s see what they contribute. Commonly, oak barrels are in question, but other options are also available. As for wineries, French, American and Hungarian oak are often used, and each has its specific addition to make. In Mlinarica, we use only barrels made from Slavonian oak, which among many coopers and barrel experts is even better than the above-mentioned ones. A good confirmation of this is the fact that a good number of these barrels are exported to France.
What we aim to achieve by aging the beers in wooden barrels is some woodiness, depending on the type of oak, and eventually the toasting of it (more commonly done for spirits). This is noticed as vanilla, coconut, nutty flavors and aromas, etc. How old the barrel is, and how many times it was used before, also dictates its potential, so a relatively new one still has plenty of tannins to leak into the beer, which gives a fuller mouthfeel. That is surely welcomed in this type of sours, since they do tend to finish really dry. After all, they stay in the barrels for a year or more, giving plenty of time to the yeast and bacteria to eat up all the sugars. However, too tannic of a feel becomes astringent, and that’s not what we’re after.
Barrel-aged sour beers have a long history, and breweries are nowadays reviving even the traditional ways of making them, while also experimenting and creating new styles.
As we said, these are more complex beers, and we recommend enjoying them after a good lunch or dinner, since the acidity and good bacteria will also help digestion.
For more information on sour beer take a look at our Mixed fermentation sour beers.
Spontaneous fermentation
Lastly, it’s time to write a few words about probably the most exciting souring technique, and that would be spontaneous fermentation. This process begins with inoculation of the wort in a shallow pool with a big surface called a Coolship. In Belgian breweries, this is often located in the attic, where there are wooden pillars and planks that already have some microorganisms living in them from previous batches.
Wort is poured into the coolship at temperatures above 50 °C, and as its temperature lowers below 40 °C, all the windows are being opened to suck in some cool air carrying yeast and bacteria that actually thrive in warm sugary liquids. Insects, of course, want to join in, but the low ceiling of the attic serves another purpose: spiderwebs! The problem with this method is the big risk factor of attracting nasty microflora, which can make our beer only suitable to pour down the drain. Our job here is to try to minimize the risks and optimize the environment, which is dependent on the atmospheric temperature and the surrounding environment (spiderwebs!).
Summer can be too hot for our friendly yeast and bacteria – in fact, Acetobacter is more likely to jump in, and this is definitely unwanted, because it even metabolizes alcohol, turning it into vinegar (we do not aim for that sour!). Winter is too cold, and many microorganisms are dormant, so spring seems the most promising.
During the spring lockdown of 2020, we took a shot at capturing some good microorganisms by taking a test batch of 20 L to a meadow and covering it with a cheesecloth. We let it inoculate for 48 h and hoped for the best. This fermentation took a while and certainly gave us a scare when it went through the puke- smelling stage, but then Brett stepped in and did its job:
we ended up with lovely fruitiness and acidity that tastes rather citrusy.
This took over a year, but we were quite delighted with the results. We are working on multiplying this culture and eventually utilizing it in our Mixed fermentation sour beers.
We hope you find all this informative enough to at least tickle your curiosity to give sour beers a chance. Cheers!
