Mixed Fermentation

This article is about sour brewing methods using commercial cultures. For other sour brewing methods, see Brewing Methods.

Introduction

For the purposes of this article, we are defining a mixed fermentation as any fermentation that consists of a combination of Saccharomyces, Brettanomyces, Lactobacillus, and Pediococcus cultures. In all approaches, Saccharomyces and/or Brettanomyces, being yeasts, will be responsible for the primary fermentation. Broadly speaking, there are two styles of mixed fermentations: "sour" fermentations and "funky" fermentations. "Sour" fermentations are characterized by their higher acidity and tart flavor, and require the use of a Lactic Acid Bacteria (LAB; generally Lactobacillus and/or Pediococcus). "Funky" fermentations generally do not contain LAB, but instead use a combination of Saccharomyces and Brettanomyces. Funky beers may be slightly tart, but are generally not considered sour.

It is important to mention that sour brewing in general has very little clear, defined "rules". Many methods can be used in conjunction with other Brewing Methods, and new methodologies are developed constantly. Many of the methods used are determined by the types of microbes the brewer is working with. This article will never be able to fully detail all mixed fermentation methods, but it will provide a "big picture" view of the general methodologies. Much more detailed information can be found in Michael Tonsmeire's pivotal book on sour brewing, "American Sour Beers".

Sour Mixed Fermentation

The Basics

Sour fermentations require at least one Lactic Acid Bacteria (LAB), such as Lactobacillus or Pediococcus, and at least one yeast such as Saccharomyces or Brettanomyces. Many yeast companies offer Mixed Cultures that provide all of the organisms necessary to make a sour beer. The results of these commercial mixed cultures can be as varied as the cultures themselves. For example some of these commercial mixed cultures produce lightly tart beer that may exhibit less funky flavors than other cultures. This is dependent on what types of microbes are in the mixed culture, what their ratios are, how old the cultures are, and of course what methods the brewer uses to encourage or discourage certain flavors. The brewer must realize that all of these microbes are complex organisms (some more complex than others), and not only due different species behave differently and produce different results, but different strains of the same species also can produce greatly different results. Just as strains of Saccharomyces cerevisiae all produce different results in clean beers (e.g., California Ale yeast versus Belgian Ale yeast), strains of Lactobacillus spp. and especially Brettanomyces spp. can also create completely different results.

Beer styles that use this method include Berliner Weissbier, Flanders Red Ale, Oud Bruin, and the subcategories of American Wild Ale, which includes Mixed-Fermentation Sour Beer and Soured Fruit Beer . European sour styles such as Lambic, Gueuze, and Fruit Lambic, technically can only be produced by Spontaneous Fermentation.

Simple Methods

The most basic method for making a mixed fermentation sour beer is to brew some simple wort (fresh extract or all grain) that is low in IBU's. Iso-alpha acids can inhibit many species and strains of LAB. Keeping the wort less than 6 IBU's is recommended in general, unless the brewer has information about their LAB culture that indicates that they can tolerate more. Mash hopping is one technique that can be used to limit the IBU's by about 70% . If hops are not required (commercial brewers may be required to use hops, while homebrewers aren't), they can be completely excluded from the recipe.

The grain bill and production for the wort doesn't have to be complex. For sour blonde ales a simple grain bill of about 70% Pilsner malt and 30% malted wheat can be used (these can be replaced by Pilsner and wheat unhopped extracts for the extract brewer. See Lambic Brewing by Steve Piatz for a good extract recipe). Some crystal and a small amount of roasted malts an be used for sour brown ales. Some higher chain sugars or even starches can be included for beers that will be aged for a long time and include Brettanomyces, or Brettanomyces and Pediococcus (Pediococcus generally should not be used without Brettanomyces. See the Pediococcus page for more details). Performing a Turbid Mash is the traditional way to include starches in the wort, however other methods such as steeping some oats or flaked wheat during the boil can also impart starches that won't be converted to sugars by the mash . This step is completely optional, however it may be very beneficial to make sure some higher chain sugars or starches are available in the wort if the brewer wants to rely on Pediococcus for producing most of the acidity. Extract brewers can use 0.25 lbs. (0.11 kg) of Maltodextrin , or hot steep a pound of flaked wheat, flaked oats, or carapils malt.

Once the wort is produced and chilled, the mixed culture can be pitched as normal. If using a mixed culture from a commercial yeast lab, it is usually recommended to not make a yeast starter with it because the starter will throw off the intended ratios of the microbes. Instead of buying a single mixed culture, a brewer can create their own mixed culture by combining their own ratios from single cultures of yeast and bacteria. A single mixed culture can be supplemented by adding pure cultures from different yeast labs as well. Another suggestion that often helps produce a higher quality sour beer is to supplement the mixed culture with a Commercial Sour Beer Inoculation. In general, the more diversity of microbes, the more complex a sour beer will be.

Aging is generally required for mixed fermentations that include Brettanomyces. Expect an aging time of at least 9 months, but preferably 12-18 months or longer. For sour beers that only use Lactobacillus and Saccharomyces, sometimes also known as Quick Sours, aging is optional. Sour beer should be aged in an environment that minimizes high temperatures and exposure to oxygen. Drastic temperature fluctuations will cause water airlocks to "suck back" air into the fermenter, which potentially could contribute to acetic acid and ethyl acetate (nail polish aroma in high concentrations) production by Brettanomyces, however the development of a pellicle will help protect against this. Filling the carboy to the neck will also help minimize the surface area of the beer that can be exposed to air. Avoid over sampling the beer (once every 3 months at the very most). It should also be noted that micro-oxygenation is helpful for creating certain flavors in sour beer, and many homebrewers have reported not having any issues with over exposure to oxygen using water-based airlocks.