OnTap Magazine

PUCKER UP HOW TO INTENTIONALLY MAKE SOUR BEER Sour, funky and wild beers are the next frontier in African craft brewing, offering a plethora of flavour experiences for the drinker and a host of new challenges for the brewer. Jacques Janse van Rensburg lays out the options for those looking to inject a little acidity into their beer. TECH TALK S ince ancient times, beer has been produced using a wide spectrum of yeast and bacteria. The typical profile of most beers would have included notes of sourness, thanks to wild fermentation with whatever happened to be floating past the fermenter. It was only in the late 19th century that the works of Louis Pasteur allowed us to develop sterile techniques to isolate and culture pure strains of micro-organisms. The most notable of these organisms for brewing was certainly yeast. Ultimately, we started using single strain fermentations in beer production which resulted in beers that could be reproduced easily for mass markets. Due to this, sour beers came to be regarded as “spoilt” and bacteria such as Lactobacillus and Pediococcus , as well as certain yeasts including Brettanomyces , were considered spoilage organisms. But despite the mass market opinion, brewers inEuropewere still usingundefined cultures to produce unique sour beers. And in recent years craft brewers globally have been showing an increased interest in sour beers, although the trend is in its infancy in South Africa. Wild-fermented beers have a niche but growing following around the world, but some brewers are understandably hesitant to invite wild yeasts into the brewery for fear of cross contamination. However, it is possible to create sour beers in a controlled manner, adding a new dimension to beer’s flavour scope. SELECTING A SOURING ORGANISM Lactobacillus When it comes to Lactobacillus , there are a few points to consider. In general, most are hop sensitive and the organisms will not grow in the presence of high IBUs. Additionally, different species of Lactobacillus have different souring capacities. Species such as L. helv eticus can produce a higher perceived acidity than L. p lantarum , while simultaneously producing different aromatic and flavour profiles. Common flavour profiles are usually regarded as “soft” and “tangy”. Commercial inoculants are often found in a format that allows for ease of use and with low inoculation rates (10g/100L) to achieve a sour wort. Yeast In terms of yeast, it is important to note that both alcoholic fermentation and lactic acid production should occur. There are certain “non-brewer” strains of yeast such as strains from the genus Lachancea that will perform a souring of the wort and fermentation to beer sequentially. Bear in mind that certain strains could also be hop sensitive which would discourage their use. Manufacturers also offer yeast in a dry format for ease of inoculation. Brettanomyces is another yeast that is often used in a sour beer. It is, however, a slow grower and does not produce a souring component itself. Rather it is used as a co-inoculant with Lactobacillus . The compounds produced from Brettanomyces can result in flavours that work well with an acidic canvas. For instance, B. bruxellensis lends earthy, woody and musty notes while B. claussenii imparts fruity-like esters. Inother parts of theworld,GMObrewer’s yeast is used where the genetic potential to produce lactic acid via fermentation was cloned into it from another organism. Wild cultures The complexity and uniqueness of sour beers obtained through wild cultures can be unparalleled. Lambic style beers use the natural biodiversity of the surrounding area to inoculate the wort. Traditionally, it would have been performed in the Zenne Valley in Belgium. Generally, the wort is cooled overnight in an open, shallow, flat metal 50 | Summer 2021 | ontapmag.co.za