Solera, a system comprising a number of vessels containing the same beverage, but of consecutive ages, the purpose of which is to create a consistent drink that can be drawn off at regular intervals. This dynamic system of maturation takes place typically in cascading stages of wooden casks. See barrel-aging and oak. Each stage is called a scale and includes the solera, the oldest barrel or set of barrels, and the criadera, a series of barrels of successively younger product. The Spanish terms reflect the fact that the solera is primarily employed in the production of sherry, although it is also used with other wines such as marsala and port, as well as rum, brandy, whiskey, balsamic, and sherry vinegars. Not surprisingly, it is also used for beer.

Author Julian Jeffs believes the terms “solera” and “criadera” first appeared in print around 1849, although they were probably in use much earlier. Gale’s in the UK, Ballantine’s in the United States, and Bayerska in Sweden were among the early production breweries to employ this technique. Belgian brewers also utilized soleras in the production of some Flemish red ales and oud bruin-style beers. Contemporary brewers utilizing the solera system include the Cambridge Brewing Company, Dogfish Head Craft Brewery, Freetail Brewing Company, and New Belgium Brewing Company in the United States, Birreria Baladin in Italy, and Norrebro Bryghus in Denmark.

Applicable to a wide range of beers including sour ales, barley wines, and strong lagers, a solera enables the consistent creation of complex beers with significant aged characteristics otherwise unattainable in most small production breweries. The process involves drawing off a quantity of the beer from the solera at set intervals and refreshing the casks with slightly younger beer of the same style from the criadera. The final product should come specifically from the oldest casks, with each level then replenished by the next oldest, regardless of the number of scales in the system. In working the scales of a solera, the brewer seeks to maintain an even distribution when topping up each older level. Therefore, if 50% of one barrel is removed, an equal amount from each barrel in the next scale is drawn out to total the volume extracted from that individual older barrel. This process is then repeated for each barrel of every level in the solera. If this is not done, significant variations can occur in the development of the individual casks.

One challenge for the brewer employing a solera is the intensive labor required to maintain proper blending techniques, particularly when topping up barrels because of evaporation. Additionally, depending upon the style of base beer being aged, the beer can often experience a considerable rise in acidity as a result of invasive or resident microflora because most beer has neither the level of alcohol found in spirits nor the acidity of wine to protect it from infection. See acetic acid bacteria, brettanomyces, lactobacillus, and sour beer. Therefore, the solera system is well suited to beer styles in which some acidity or wild yeast character, whether originally anticipated or not, may bring about a pleasing complexity. Proportional blending from each barrel in the solera is sometimes required because certain barrels can express a propensity for producing higher degrees of attenuation or acid concentrations than others. A balanced and consistent beer is the goal every year.