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Methods of creating sour beer without using ''Brettanomyces'' are also considered a form of mixed fermentation. Since ''Brettanomyces'' is removed from the process, these methods tend to create a sour beer in a shorter amount of time, but without the complex ester and phenol profile of ''Brettanomyces''. Kettle souring and other methods of souring wort before pitching brewer's yeast, as well as pitching lactic acid bacteria after primary fermentation with brewer's yeast, are examples of this process. See [[Wort Souring]] and [[Alternative_Bacteria_Sources#MTF_.22Reverse_Kettle_Sour.22|MTF "Reverse Kettle Sour"]].
==Finishing Mixed FermentationsFermentation Sour Beer=====Determining When It Is Done===Unless the brewer has worked with the same blend of microbes and wort recipe, it is difficult to give an exact time frame on when a mixed fermentation beer might be ready. Anywhere from three to twelve months is a reasonable amount of time, but where the beer will fall in-between this time depends on many factors including microbes pitched, their health over time, and wort composition. The best guide is a long-term stable gravity: if your gravity has remained stable between several readings over a month or two, then your beer may be ready for packaging. The second factor is how does the beer taste? If it tastes good, and the gravity is stable, then you can package it. If the beer does not seem to have a mature flavor from the Brettanomyces and has off-flavors that need to age out, then feel free to age it longer. Some off-flavors will change even when bottled or kegged, but others (such as sulfur-based compounds) will need to dissipate out of the fermenter slowly over time. ===Bottling and Kegging===See the [[Packaging]] page.
===Reusing a Sour Yeast Cake===
Reusing a sour yeast cake can often provide great results. Brewers have reported success re-pitching on very old yeast cakes (2+ years) without getting off flavors from yeast autolysis. After several months, ''[[Saccharomyces]]'' tends to die off due to the low pH in a sour beer. The bacteria and ''[[Brettanomyces]]'' tend to survive the lower pH, and their cell counts can be high depending on how old the yeast cake is (interestingly, ''Brettanomyces'' remains more viable over time if it was co-fermented with ''S. cerevisiae'' than if it was fermented by itself; i.e. [[100%25_Brettanomyces_Fermentation|100% ''Brettanomyces'' beers]] <ref name="Hubbe"></ref>). By pitching new wort on an old sour yeast cake, these microbes (particularly the [[Lactobacillus]]) have access to the simple sugars in the wort <ref>[http://www.themadfermentationist.com/2009/11/brewing-sour-beer-at-home.html Tonsmeire, Michael. The Mad Fermentationist. Brewing Sour Beer at Home. Last paragraph in the "Inoculation" section. Retrieved 2/19/2015.]</ref>. Using a young yeast cake is also a viable option, and may carry over more surviving ''Saccharomyces'' cells as well as more viable cells of the other various microbes. In general, [[Laboratory_Techniques#Yeast_Rinsing.2FWashing|rinsing or washing the yeast cake]] is not necessary ([https://www.youtube.com/watch?v=9LXEAZbei_8 acid washing] can kill the bacteria). The beer itself can also be used as an inoculate and might be more desirable so as to avoid trub. If the beer has sat in a barrel ''Acetobacter'' and other unwanted microbes might be more present on the surface of the pellicle, and would remain after racking the beer out of the barrel, so some professional brewers advise using beer as an inoculate for this reason <ref>[https://youtu.be/IGzoh4brILA?t=52m30s Yakobson, Chad. Interview on Craft Commander. 12/20/2016. Retrieved 12/22/2016.] (~52 mins in)</ref>. If the yeast cake is particularly old, perhaps say older than 1 year, or has a very low pH (low 3's), then making a starter with the slurry will help guarantee the viability of the microbes. Such a starter can be treated the same as a [[Mixed_Cultures#Starters_and_Other_Manufacturer_Tips|mixed culture starter]] that can be assumed to not have any viable ''Saccharomyces''.
See the [[Mixed_Cultures#Starters_and_Other_Manufacturer_Tips|mixed culture starters]] section for more information on starters for mixed cultures.
==Quality Assurance and Avoiding Cross Contamination==