MSc Project > Introduction

This post is part of a series detailing the findings of my MSc research project which looked at the effects of different fermentation parameters on wort souring with Lactobacillus. If you haven’t already, take a look at the MSc project page for a full overview.

Sour beers have experienced a staggering change of fortune in recent years, going from fairly obscure and in some cases nearly extinct, to staples for many breweries and dare I say it, more or less mainstream.1 Their brisk rise in popularity has also been accompanied by a resurgence of interest in sour production methods. The numerous challenges associated with using more traditional sour brewing techniques in modern breweries has compelled brewers to experiment and innovate. As Tonsmeire documented in American Sour Beers, many examples now exist where hybrid methods have been adopted, combining elements from both modern and traditional processes.2

For many modern breweries there are a number of barriers to making traditional mixed-fermentation sour beers. They often require extended ageing times, from months to years to fully mature, necessitating both vessel capacity and cellaring space. There’s also a heightened risk of microbial cross contamination if brewing clean beers in the same facility. These drawbacks have lead brewers to adopt a number of alternative approaches to address these concerns.     

One of the faster techniques now commonly used to make sour beers is through the biological acidification of wort before alcoholic fermentation with yeast. This is typically achieved by adding a culture of lactic acid bacteria (LAB), which produce lactic and other organic acids as the major metabolic products of lactic fermentation. Lactic acid is the dominant acid responsible for the sour taste in beers made by this method. Lactobacillus is a genus of LAB that is widely used for this purpose, either as a single strain culture or a mixture of strains. The reason for its popularity is that it grows well in barley malt wort and given the right conditions will produce large quantities of organic acids in a short period of time. Acidification techniques can be broadly categorised based on whether the souring step occurs before or after wort boiling. The main advantages to boiling wort after acidification with LAB are that the risk of contaminating any downstream equipment is negated and a more conventional hopping schedule can be used.

The objective of this study was to determine the effects of changing different lactic fermentation variables on the wort souring performance of Lactobacillus. To achieve this, a series of small scale lactic fermentations were performed for 72 hours. Using a single Lactobacillus strain the influence of independent variables: temperature, wort gravity, pH and inoculation rate were examined. The acidification performance was monitored by measuring both pH and total acidity.


  1. Pattinson, R. (2017) German sour beers of the late 19th century, Tech. Q. Master Brew. Assoc. Am., 54, 132-137.
  2. Tonsmeire, M. (2014) American sour beers, Brewers Association, Boulder, Colorado, USA

Leave a Comment

Your email address will not be published. Required fields are marked *