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Fermentation Vessels, also known as fermenters or FVs (and occasionally spelled fermentors), are the tanks, barrels, or other vessels where wort is held as it ferments into beer.
Fermentation vessels have always been an essential part of even the humblest home-based brewery. They have been almost infinitely varied over time; almost anything that can hold liquid can be a potential fermenter. That said, the technology used for fermentation vessels has progressed considerably during the past 50 years.
History of Fermentation Vessels
Historically, the development of fermentation vessels has very closely reflected the development of brewing methods and technology. The first beers were probably fermented in animal-skin pouches and carved wooden bowls. Starting in the early Sumerian and Egyptian civilizations (circa 4000 bc), from whence we have the first written records of brewing, the vessels used were ceramic amphora-like jars, probably up to a few hundred liters in size. These ceramic jars remained the fermentation and storage vessels for most beers (and also wines) for thousands of years.
It is in the period between 500 and 1000 ad that we see the first historical evidence of brewing methods in northern Europe. By this time the preferred fermentation vessel was made of wood, usually oak, and oak remained a preferred material well into the 1800s. See oak. Raw unlined wood was used at first, but by the 1800s most wooden fermentation vessels were lined with some sort of tar, pitch, or resin. The lining acted as an inert surface that prevented the beer from coming into direct contact with the rather soft, rough, and penetrable surface of the wood. Lined wooden vessels could be cleanedmore effectively, thus significantly increasing the stability of the beer against both microbiological infection and off-flavors from the wood itself. Wooden fermentation vessels were constructed in various dimensions—small or large, open or closed, upright or horizontal. Until quite recently, the fermentation vessels at Pilsner Urquell were still a forest of open wooden vats, each on its own pedestal. See pilsner urquell. By the time of the Industrial Revolution, many wooden fermenting vessels were enormous in size. The most famous (or infamous) of them was a fermenting vat at the Meux “Horse Shoe” Brewery in London. See meux reid & co. This wooden fermentation vessel was 22 ft tall and held over a half million liters of fermenting beer. At 6:00 pm on October 17, 1814, one of the 29 giant iron hoops that secured the vessel snapped. The vat burst, causing a chain reaction with surrounding vats, blowing out the wall of the building, and flooding the street. Two houses were washed away and nine people died in the “London Beer Flood.”
Cylindroconical tanks at the Paulaner Brewery in Munich. Cylindroconical tanks have a slanted, cone-shape bottoms which, among other advantages, allows brewers to easily remove yeast for disposal or repitching.
This incident, among others, spurred breweries to begin looking for other materials than wood for large fermenting vessels. Later in the 19th century most new and expanding large breweries would include square concrete fermentation tanks lined with resin, asphalt, slate, or enamel. Here is a description of a 19th century–style London brewery, as described in 1911:
The next process is that of fermentation, which is carried on in a splendid room below, the floor of which is constructed entirely of slate. It is known as the “Havelock Room,” having been built at the time of the Indian Mutiny, and is shaped like the letter L with dimensions of 210 ft. and 132 ft. Here are contained fermenting vessels of slate and wood, each provided with a copper parachute for skimming yeast, communicating with the yeast tanks below. Each of the vessels holds from 120 to 190 barrels and contains an attemporator to raise or lower the temperature of the gyle at pleasure. This contrivance consists of a series of pipes fixed within the tun and having its inlet and outlet on the outside; by this means it is possible to run hot or cold water through the pipes at any hour.
Active fermentations give off considerable heat, and fermentation temperatures can rapidly rise to a point where flavors and yeast health are adversely affected. The ability to cool fermenting beer was therefore important, especially during the warm summer months. The introduction of mild steel tanks coincided with the spreading use of industrial “artificial” refrigeration. First introduced at Germany’s Spaten Brewery in 1871, artificial refrigeration allowed fermentation vessels to be cooled by means other than the “natural” cooling achieved by digging deep fermentation cellars. These cellars had been cooled by vast quantities of ice cut out of rivers and lakes in winter and then placed over the cellar ceilings and below cellar floors. In the early days of refrigeration, cooling of fermentation vessels was achieved either by circulating refrigerated air in the fermentation cellars or by circulating cooled water or brine through metal coils inside the tanks. Normally the coils were made of copper or brass because these materials both conduct temperature efficiently and are not corroded to a major extent by wort or beer. The cooling coils would be placed along the sides or the bottoms of the fermentation vessels. By manually opening and closing the valves on the cooling coils, it was possible to rapidly chill beer, even during active fermentation. However, this method remained primitive and the temperature from vessel to vessel could vary greatly because the tanks were both open and uninsulated.
Around the turn of the 20th century, rapid industrialization brought the widespread use of mild steel for all types of construction. Mild steel became the preferred material for building fermentation vessels. Because mild steel is very susceptible to corrosion by acidic liquids such as beer, direct contact with beer would cause the vessels to rust, giving the beer a notable metallic flavor and aroma. Thus, mild steel tanks had to be lined, and the preferred materials for this were enamel, glass, and later epoxy-type polymer materials. As long as the enamel or glass lining stayed intact, this was a perfectly sanitary and easy-to-clean inner tank surface. However, both enamel and glass are very brittle materials that eventual start to chip and crack, as does epoxy. Many brewery operations remained manual, including tank cleaning, and men had to enter these vessels and hand scrub them after every use. The linings were easily damaged but very difficult to repair.
One thing was improving; although open fermentation was still practiced by some large American breweries into the 1970s, the norm in the United States slowly transitioned to completely closed fermentation. This made fermentation more sanitary and eased the collection and reuse of carbon dioxide created by the yeast.
Around 1920, aluminum became affordable, and many breweries started installing fermentation tanks made of this much lighter metal. Aluminum had the huge advantage of being resistant to corrosion by wort and beer and could therefore be used without having to apply a brittle inner lining. One major disadvantage of aluminum, however, is that it is corroded by caustic soda (sodium hydroxide), which has for many decades been the preferred detergent for cleaning brewery equipment.
Soon after the introduction of aluminum, stainless steel was introduced as a construction material on an industrial scale. This material offered many advantages when used in breweries in general and to this day is the undisputed first choice of material for constructing fermentation vessels. Also, piping, pumps, valves, and almost all other brewery equipment that comes into direct contact with beer are made of stainless steel.
Until the 1960s, whether constructed from mild steel, aluminium, or stainless steel, most fermenters were cylindrical in shape and positioned horizontally. Usually they were stacked in several layers in the fermentation cellars, and it was uncommon to individually insulate the tanks because this was relatively expensive. For this reason, all fermentation vessels were used for primary fermentation only, so when active fermentation had finished, the beer would be moved by means of pumps and hoses to another tank in a separate cellar for the final maturation. Bottom-fermented (lager) beers would be placed for extended periods of time at low temperatures in the lagering cellars, whereas ales would be usually be transferred into a third cellar full of storage or racking tanks before being packaged.