I love how beer and brewing just keep evolving. A few basic choices spawn a rainbow of beer styles to fit every taste. Then, certain exotic flavors with maybe one or two examples expand like the rare-elements section of the periodic table.
Sour beers are a case in point. Once they were mainly represented by Belgian lambic, Berliner weisse, and sanitation errors. Except for that last one, they were not particularly easy to brew at home.
To tackle a lambic-style beer, you’d have to find or cultivate a list of special bugs to infect your wort, and you probably ought to have a wooden barrel, if only for the ambiance. The Berliner path was somewhat less daunting, but its character was more simplistic than its Belgian cousin. Brewers exploring this corner of the beer world eventually popularized the technique of kettle souring. In turn, that helped lead to the revival of gose, whose brackish wheat base has become a pliable foundation for a multitude of spiced and fruited specialty beers. These days, the average bottle shop is well stocked with beers based on those methods, even when they don’t bother to reference either of those styles.
This explosion of “quick sours” may seem to be a fresh fashion, veering away from the mainstream, but these light, tart beverages are not a completely new trend. Traditional citrus-based beer mixes such as shandy, radler, or michelada have long been perfect for summer refreshment. The new element is how brewers have expanded beyond a mild, simple, sour flavor into a wild spectrum of combinations.
With so many interesting choices on the shelves, why bother brewing your own? For that matter, you could even blend your own beers with whichever flavorings you choose. The obvious answer is the joy of brewing, but the relative simplicity of the kettle-souring process makes it easy to try.
There are three main techniques to introduce acidity into your beer. All three are fairly straightforward and will give you the tartness you seek; the best choice depends on your brewing skills and preferences.
The easiest way is to simply add lactic acid to the wort or finished beer. This provides absolute control of the acidity because you can taste-test drop by drop if you’d like. Plus, there’s very little chance of an outside infection. The main drawback is that it’s likely to produce a simpler, less nuanced sour character (and, some might argue, it’s cheating). The other two approaches rely on pitching a living Lactobacillus culture and letting it naturally produce the acid.
All-grain brewers have the option of getting a good, assertive bite by adding the Lactobacillus directly to the mash. To do it, they just run through their normal mash schedule, then cool it down to a safe range before adding the bacteria. After letting it sit for a day or more, they move forward with sparging and boiling.
Good news for extract brewers: The other alternative is to add Lactobacillus to the wort. In this case, it doesn’t matter whether the wort came from extract or your mash tun.
These approaches with Lactobacillus will give you some acid and reasonable control over it, and the culture will also produce other esters with subtle flavors such as geranium, raspberry, or woody notes.
Given the trade-offs, let’s go forward with a natural Lactobacillus culture pitched into an extract-based wort. We’ll get the most interesting character that way, and it’s well within the skills of any experienced homebrewer.
Acidifying the Wort
Here’s the basic process:
Prepare the wort.
Besides the normal step of dissolving the dry malt extract (DME) in hot water, we’ll also want to lower the pH—to between 4.0 and 4.3—using a little lactic or malic acid. Once that’s ready, boil the wort for 10 minutes to eliminate any competing bacteria or wild yeast, then cool it to the right temperature for the Lacto culture (roughly 95–113°F/35–45°C). It’s also important to understand that hops inhibit the lactic-acid production of Lactobacillus, so any hops additions should wait until the second boil, after souring.
Inoculate the wort.
There are a number of sources for Lactobacillus, from active-culture yogurt to more standard pitchable forms. Like yeast, these can be liquid or dry cultures. (Any will work well, but in our recipe, I go with White Labs WLP693 Lactobacillus plantarum.) Once the wort is inoculated, the bacteria need time to do their work without any competition. If you have a kegging setup—and thus CO2 on hand—I recommend adding a blanket of CO2 to the kettle headspace before sealing the critters in safely. Either way, cover the top of the kettle with plastic wrap and then put on the lid.
Walk away for a while.
Once everything is sealed, it’s a waiting game while we hold the kettle within the optimal temperature range for the Lactobacillus. The souring process can take anywhere from several hours to two or three days, and brewers will often pull samples along the way to check whether the pH has hit their target (usually 2.7–3.0). Once you’ve got experience with a couple of quick sours, you can do more frequent checks, but I recommend a simpler approach for your first one: Just let it sit for a full day, then go with whatever the Lacto gods have bestowed upon you.
Once the Lactobacillus is done, your brewing process is back on familiar ground. Start your boil as if it were a regular batch of beer. The boil will kill off the bacteria, but the lactic acid will remain. As I mentioned before, if your recipe calls for hops, you can add them now, when they won’t hurt the Lactobacillus. Post-boil, chill down the wort as usual and pitch your yeast. Don’t be surprised if the fermentation is a bit sluggish; the yeast won’t be quite as happy in their low-pH home. That’s why you should use a fairly strong yeast strain with a good starter.
Now that you have the basics of kettle souring, consider the specifics of your beer. As I mentioned, these beers are often derived from Berliner weisse or gose, but let’s just aim for something light and refreshing with a wheat-beer base. We don’t want a lot of distraction from specialty malts, so we’ll use a simple wheat-malt extract. If we stop here, we’ll end up with something like a kettle-soured Berliner weisse, but a big part of the fun is exercising the creativity to find something more unique.
That immediately suggests exploring fruits and spices. Any tart fruit would play nicely with a kettle sour, so berries and tropical fruits are all on point. While it’s not a fruit, hibiscus flower is another fruity flavor that works well in these beers. I recommend that you limit yourself to one or two items. If you try to combine too many fruits, it can turn out muddled, like an amorphous fruit salad.
When it comes to spices, consider what would play well with the fruits you selected. You might even want to try out the combinations beforehand, just as finger food or flavored juice. Something that seemed like a good idea on paper might not pan out. Most importantly, keep in mind that fruit is fairly forgiving, but spices are easy to overdo; restraint is paramount. Similarly, if we’re building up a good fruit-spice combo, we need to be light-handed with our hopping, too.
For our recipe, I decided on a pomegranate-mint combo. Perle hops have a light spicy character that I think would fit nicely, but Saaz would also work well. Like many sour beers, the focus will be on a light hop flavor, not bitterness.
Photo: Matt Graves/mgravesphoto.com