Sourness in beer is traditionally associated with ‘off beer’, so it can be a hard sell to people who are new to sour beers/the taste of sour beers. However, I’ve found that I have more success converting non-beer drinkers with sour beer rather than something more typical like a lager or a pale ale. I think the main reason behind this is that sour beers are generally low in bitterness, but another factor is that the sourness means that sour beer has more crossover with other beverages that haven’t typically eschewed this aspect of the drinking experience, namely ciders and wines.
When you drink a sour beer and experience that puckering sensation, you are normally drinking a couple of acids. The most common is lactic acid, that provides a ‘clean’ sourness; not contributing tons of flavour or aroma, but adds a crisp and refreshing tartness. At low quantities it can add a pleasant brightness to a beer, but in high concentrations it can be mouth-puckeringly tart, and even contribute slightly sicky aromas. The other common acid is acetic acid, which is more commonly known as vinegar. This is less common than lactic acid, since it has a far more pronounced and aggressive flavour and aroma, but can be quite pronounced in Flemish red ales and lambic beers.
As mentioned in a previous blog post, brewers can have some degree of control over how sour to make a beer. But since sourness is a tasting experience, how can that subjective experience be translated into reliable and repeatable data? pH (subject of another blog post) is adequate at getting a measurement for sourness ‘in the right ballpark’, but since pH is a logarithmic scale, using it as an accurate measurement of sourness is flawed. Purely relying on human taste buds again works ok enough (I actually prefer it over using pH), but is open to varying results depending on a myriad of factors.
The most reliable is a test called a titratable acidity test. The brewer takes a measured sample of the beer, then in 0.1ml increments, adds 1 Mol of sodium hydroxide. The sample is stirred and then the pH is measured. Sodium hydroxide is added in this way until the beer sample reaches a pH of 8.2. Then a formula is applied (yay maths):
(ml of 1M NaOH solution used) x 9
weight of beer sample (g)
= % of acid OR titratable acidity (g/L)
This system is of course not perfect. It can only be used to measure one acid at a time (the above test is for lactic acid), so it can become difficult for beers that have many types of acid in them such as lambic beers. It is nonetheless an excellent tool to quantify how much you are set to pucker your customers’ mouths.