Solera

For the traditional Solera process used in Sherry, vinegar, and brandy production, see the Wikipedia article on Solera. In beer, particularly sour beer, a single stage Solera process has been discovered to be a reliable and easy way to continuously make sour beer. Some have argued that this is a misuse of the word "solera" and that it should only be applied to multiple tiered systems (see Misuse of the Traditional Meaning below).

The process of using a solera method in sour beer brewing has become the term used for filling a single fermenter with a sour beer, and every 6-12 months taking one third or half of the beer out for packaging (sometimes as much as 70% is taken out, although there is no set definition on what percentage must be left behind in order to still be called a "solera"). That volume is then replaced with new beer or wort. This method provides the brewer with an "perpetual" sour beer that takes less time to age because of the blended components. Over time the beer can continue to develop and change, and the brewer has the option of trying to steer the beer by altering the recipe for the wort or beer used to refill the solera. As a rule of thumb, the larger the fermenter the better. This will allow for larger seasonal pulls from the solera, thus producing more beer. The term could also be applied to a multi-vessel solera in beer, which has been argued is a more accurate use of the term, although multi-vessel solera systems in sour beer production are less common due to the potential for over exposure to oxygen.

The barrel can be refilled with either fermented beer or wort. Choosing to refill with wort could eventually lead to a lot of trub build up, however, there might not be any negative flavor effects from doing so. Wort will ferment in the barrel and might cause a blow off unless there is adequate headspace (in which case the brewer should top up the barrel after the wort ferments). Choosing to refill with beer that is first fermented with brewers yeast or with a mixed culture might be more practical for avoiding blow off issues and for group barrel projects for homebrewers because individual brewers can brew the refill beer at any time, and then meet to refill the barrel. See Yeast Autolysis below.

Misuse of Traditional Meaning

The term "solera" has deep roots in the history of Sherry production dating back as far as the late 1800's. As such, the term has a fairly strict and traditional meaning in the Sherry and wine industry. See this article by Ruben Luyten for an in-depth definition of the solera system as it is known in the Sherry industry. As a part of the traditional solera system, multiple tiers of casks are used in the system. There appears to be no known use of the term "solera" in the wine industry to apply to a single tier blending system (this is referred to as "perpetual blending" in the wine industry). As such, some brewers argue that unless a solera consists of multiple tiers, such as the system at Cambridge Brewing Co. for Cerise Cassée, which is the oldest known beer solera since 2004, that it is not a true solera. The alternative term "perpetual blending", which has been applied in wine world to refer to single vessel blending systems , has been offered as an alternative and more accurate word to use for single-vessel blending systems.

There are arguments defending the use of the term "solera" in the brewing industry and in homebrewing to refer to single-vessel blending systems. These include:

• Terms are borrowed and changed all the time, and that the nature of language is to evolve.
• The term has been used since at least 2006 by homebrewers to describe a single-vessel blending system .
• Reversing the precedence of calling single-vessel blending systems something other than "solera" will be impractical now.
• The brewing of the fresh beer in a steel fermenter could be viewed as the "first stage of a solera", so as long as fresh wort is not added, it is still a solera (this argument is countered by the term "secondary" being used in brewing to rack liquid from one fermenting vessel to another).
• The term "perpetual blending" is less marketable than the term "solera".

A full debate of these points and counterpoints can be found on this MTF thread, with comments by Will Meyers of Cambridge Brewing Company. As with the usage of the term "lambic" and others, we encourage readers to read the arguments on both sides and develop their own informed opinions.

See also:

Yeast Autolysis

Yeast autolysis is the rupturing of dead yeast cells and produces meaty or rubbery off flavors . When it comes to sour beers, Lambic producers often let their beers age in barrels on the trub for up to four years without effects of off flavors from yeast autolysis. The hypothesis is that the Brettanomyces will metabolize the off-flavor compounds produced by the bursting Saccharomyces cells, and use them as nutrients . Therefore, many people have reported that they have successfully avoided yeast autolysis in solera projects, as well as just allowing sour beer to remain in the primary fermenter for the entirety of its aging. However, as the solera ages, trub buildup can potentially become be a problem for logistic reasons (such as clogging ports). Will Meyers of Cambridge Brewing Company reported an eventual autolysis issue with his solera . Lauren Limbach of New Belgian Brewing reported tasting "goaty", "dog food", "caprilic and capryc" flavors in barrels that had not been cleaned out after a few years, and upon rinsing the barrels out with de-aerated water the resulting beers were "bright and beautiful" (the barrels were filled with clean beer and not inoculated; assumably the microbes surviving in the wood were enough to produce good results) (~37 minutes in).

Whether or not the brewer elects to refill the solera with wort or fresh beer can also potentially play a role in yeast autolysis issues eventually creeping up in a solera. If flavor issues from yeast autolysis are going to occur, adding wort will create a thicker trub, which could lead to autolysis issues faster. In either case, theoretically, these issues can be avoided. One method for avoiding off flavors from yeast autolysis is to rack some of the trub out of the solera when the seasonal pulls are taken. Another method is to rack the solera to another vessel once a year or every other year. Once removed from the trub, the Brettanomyces should be able to clean up the off flavors over time. See also Reusing a sour yeast cake.

See also:

• Will Meyers of Cambridge Brewing Co. shares his experience with autolysis and running the oldest commercial solera program for sour beer in the US.

Articles on Solera

• Starting a Solera, by Ed Coffey on HBT. This is a great article on what a solera is, and how to start one for sour beer.
• Michael Tonsmeire has several great articles on Solera. Some noteworthy articles:
  • Sour Solera Beer Barrel
  • Second Pull Wine Barrel Solera - touches on the yeast autolysis issue.
  • Interview with BasicBrewing on Solera, and Solera Average Age Spreadsheet.
• Farmhouse Beer Blog, Outside the Box Solera - Details on Sherry solera production, and how it relates to beer production.
• Adam Kielich's blog on small batch Solera and blending pulls to make a Gueueze.
• Dan Pixley's solera project over the last 3 years in video playlist format.

In addition, see the Blogs Wiki page for blogs that may contain more articles on solera.

See Also

Additional Articles on MTF Wiki

• Mixed Fermentation
• Brettanomyces

External Resources

• Old Walloon Ale; a 200 year old solera.