CLASSIC beer-making technology
What preceded CCVs
It should be noted that in the history of brewing, a variety of materials were used to make fermentation vats: from wood and ceramics to aluminum and plastic. Usually brewers used improvised material, guided primarily by one principle: it should behave fairly neutral towards an aggressive (in a chemical sense) alcohol-containing acidic medium, i.e. beer.
As early as the first half of the 20th century, a classic fermentation vessel (or lager vessel) was wooden. Oak was traditionally used, less commonly pine or cypress vats. In their shape and design, they resembled traditional but bigger-sized Russian tubs (a truncated cone). There were no specific standards for the capacity of wooden barrels. Fermentation vessels could be 2 to 300 hectoliters, and lager vessels could be 100 hectoliters. The only limiting factor was the maximum tolerable size of a wooden rivet framing the vessel. The fermentation process in wooden vessels was absolutely natural and unhurried. Wooden barrels were cooled outside.
The thick yeast cover forming on the surface naturally preserved carbon dioxide in the beer, playing the role of a sort of cap and shielding the beer from bacteria to some extent. Inside, the wooden fermentation vessels were covered with a special "beer frankincense" (the main components were rosin and paraffin) protecting wood from the destructive effects of beer and enabling vessel sanitizing operations in due course.
Considerable importance was given to the process of beer stone depositing on the surface of a wooden (later – concrete) vat. Often after removing the plaque of beer stone from the inner surface of the vat, which was inevitable when the tank was thoroughly cleaned, the further process of yeast deposition and beer clearing was slowed down somewhat. Its flow "returned to normal" only after the beer stone reappeared on vat walls.
Beer fully fermented in an oak vat acquired a specific taste that is an essential sign, according to old Czech technologists, of "good natural beer." This was not the last reason why many Czech breweries (including the famous Prazdroj a.s.) used wooden vat back in the second half of the 1980s. The Czech people, as everyone knows, are not too willing to apply innovations in the brewing process, believing that the majority of innovations have a negative impact on beer organoleptic properties.
The main disadvantage of wooden containers was that they required very laborious service. Inner surfaces needed to be refreshed at regular intervals as appropriate. Refreshing intervals for inner surfaces were not strictly scheduled. As a rule, this procedure was held once a year.
According to Zdeněk Šubrt, ex-technologist of Plsensky Prazdroj a. s., now UBC employed as a brewery technologist, each time after the end of fermentation, barrels had to be removed from the racks and raised from the basement by using a special elevator, carefully cleaned from the old coating of frankincense (by blow lamp firing), applied a new coating and placed back to their original locations in the basement on special racks. Therefore, when high-quality oak boards from which riveting was made passed into the "low-supply" (and, accordingly, very expensive) product category, reinforced concrete and metal vats replaced the wooden ones. Maintenance costs for concrete and metal containers were lower, and service life was longer.
Today, it's hard to believe it, but reinforced concrete vats were commonly used in Europe in the second half of the twentieth century. Inside, they were covered with a layer of special coating or a thicker lining. Rock wax, plastic, or epoxy resins were used as the base of the protective material.
Metal vats were mostly made of ordinary (black) steel, less often – aluminum, even less often – stainless steel (stainless steel was very costly). From the outside, the metal vats were insulated with resin and jute and then laid over with bricks. They were brick-lined only to avoid having to clean not only the inside but also the outside of the vat.
The most affordable vats were made of ordinary steel. This material is well processed and is quite durable. When making a fermentation tank, its steel sheets were often welded together right at the brewery. One of ordinary steel's disadvantages is the "increased sensitivity" to beer medium: acids formed during fermentation act "etchy" on the steel surface. This produces tannins that give the beer its distinctive irony flavour and darker colour. The foam of this beer gets a brown hue. To avoid such a result, ordinary steel was coated with a protective coating of enamel, synthetic resin or plastic. The size of enameled vats was strictly limited to the size of the kilns in which enamel was fired. However, in the Czech Republic, brewers learnt to apply this method for making 500-hectoliter vessels.
Aluminum acted as the protective coating for the reinforced concrete vat in aluminum vats.
Side sheets were some 3 mm thick, while the bottom sheets were about 4-5 mm thick. Aluminum vats were brick-lined to become more robust. It was necessary to ensure carefully, when assembling the container, that the vat's aluminum did not come into contact with any pieces from another metal. Otherwise, the beer filled container was like a giant battery: beer played the role of acid, various metals played the role of different pole contacts, and the "battery" itself started generating galvanic currents.
If there are no cases of galvanic corrosion, aluminium is completely inert to beer. An aluminum vessel requires no protective coating. An aluminum vat's main drawback is its low strength because it is easily distorted. Aluminum lager vessels are very sensitive even to a touch of internal vacuum. To make a stainless steel vat, ca. 2 mm thick steel sheets were used. They also acted as a protective coating of concrete. It is commonly believed that stainless steel used in the brewing industry should contain an average of ca. 18% chromium, 8-9% nickel. Such stainless steel is absolutely inert to beer and fermentation products, but the initially high price of this material has long been preventing its widespread use in brewing.