For the past few years, sour beers have been growing in popularity, both on the commercial scene and among homebrewers. We’ve seen a few all-sour breweries appear, many tasty one-offs from breweries of all sizes, and some breweries that have committed to a sour brand in their lineup. Homebrewers have been represented soundly on the competition circuit as well, with barrel-aged Flanders reds and browns, “pseudo Lambics (pLambics),” Berliners, and more recently, the Gose, that salty wheat beer from Goslar and Liepzig, Germany.
For the most part, brewers have been content to take their best stab at a recipe and “get what they get.” More recently, however, notable strides have been made to achieve better predictability, cleaner profiles, and repeatability. A big piece of this has been closer monitoring of pH on the front side and recording titratable acidity (TA) in the finished beer, especially for blending purposes.
If you’d like to go a bit deeper in your own attempts at sour beers, it isn’t too hard to shorten the learning curve and make all that time and effort count with just a bit of understanding and a few measurement tools.
The first thing to understand is exactly what the difference is between pH and TA. They are not the same, not even directly corollary, and certainly not interchangeable. Where pH measures the dissociated “free” hydrogen ions in the balance of acids and buffers in a solution, TA approximates the amount of total acidity, associated or dissociated, by measuring how much of a strong base (generally sodium hydroxide) it takes to reach an endpoint of pH 8.2.
Since we taste acids rather than pH, it’s the TA that better predicts the perception of sourness of a beer. In practice, a beer with an appropriate amount of TA will also have a fairly low pH (and vice versa). That said, it’s entirely possible to find two beers with equivalent pH and very different levels of perceived sourness due to the differences in the various weak acids that make up a sour beer—notably lactic and acetic, with small amounts of succinic, malic, citric, and other acids.
To find TA, you need an acid test kit, available at most homebrew shops. These come with a color solution (say “phenolphthalein” three times fast!), sodium hydroxide (lye), a graduated syringe, and instructions. Sodium hydroxide is a strong caustic chemical so use caution and definitely dispose of the sample after reading. Most acid testing kits are designed for wine and will give an adjusted reading of tartaric acid in g/L. Most sour beers will range from 0.30 to 0.75 percent TA, but remember that the measurement should not be taken from the wort. The finished beer provides the final number we are looking for. Carbonation levels, residual sugars, alcohol levels, hops bitterness, exact composition of the various acids, etc., all play into the final effect.
While TA measurements may be a better predictor of sourness, pH is still a valuable measurement for a few reasons. It’s pH that informs your hops utilization, ensures hot break, and helps improve shelf life and color stability. Measuring pH is very simple, but be aware that test strips, though inexpensive, are notoriously inaccurate and are not of much use for making sour beer. An inexpensive pH meter will do the job if it is maintained well and calibrated with each use.
Now that you have an understanding of what TA and pH mean and how to measure them, let’s look at how to use these values when you’re brewing a sour beer. If you’re looking to do a kettle sour beer by bugging the wort with Lactobacillus pre-boil, the recommendation is to drop the pH of the wort down to 4.0–4.5 before inoculating to inhibit growth of the less desirable bacteria. You can adjust the pH to below 4.5 either with phosphoric or lactic acid or by using acidulated malt for a portion of the grist.
Once you have the appropriate pH in the wort and have inoculated it with the Lacto, monitor the pH during the souring process for a quick measure of when to stop the activity and pasteurize/boil the wort. A kettle-soured wort of pH 3.7 or lower will be noticeably tart, with 3.0 delivering an extremely mouth-puckering sourness. Keep in mind that if you plan to perform a full 60-plus minute boil, your acidity will drop further. Also keep in mind that a high carbonation level, which is common with sour styles, will drop the pH 0.1–0.15 points. That means that if you are looking at your finished beer’s pH and want to replicate it, the next round’s flat beer will measure a touch higher before carbonation.
With good pH and TA measurements to inform our inoculation, souring, and blending processes, we can get closer to that perfect sour beer. And should we stumble upon it, we might even have a good chance of re-creating the magic!