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.
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.
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. roger putman
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.
Developments continued during the late 1800s with upright cylindrical vessels, some with sloping or conical bottoms. In 1960s a breakthrough in technology advanced a new principle—primary fermentation and maturation could be carried out in the same vessel. The breakthrough was the modern “cylindroconical” tank, an upright cylindrical tank with a slanted, cone-shaped bottom. These were dubbed “universal tanks,” or unitanks for short. Unitanks became widespread in the 1970s, and over the past 40 years the cylindroconical tank has—with a few important exceptions related to the brewing of very traditional beer styles in Belgium and on the British Isles—replaced all other types of fermentation vessels. It has been commonly accepted in the brewing industry that cylindroconical tanks have numerous advantages over all older tank designs:
Interestingly, the cylindroconical tank has roots back to patents dating from 1908 and 1927, but the revolution in stainless steel fabrication was necessary to make the manufacture and use of such tanks practical. The proliferation of cylindroconical tanks began in Ireland in the early 1960s, where vertical (i.e., cylindrical tanks standing upright) stainless steel tanks of up to 11,500 hl (9798 US bbl) were in use. In 1965 the Japanese brewery Asahi patented a large vertical tank with a sloped bottom, allowing the yeast to be harvested from the low side.
The overall geometry of tanks was also being explored in the 1970s and 1980s, resulting in taller and slimmer cylindroconical tanks, which saved floor space. However, it was soon found that once these so-called rocket tanks (in reference to their appearance) exceeded a height-to-diameter ratio of 5:1, good mixing could not be achieved and the yeast suffered from excessive hydrostatic pressure. Thus, today cylindroconical tanks are generally built with height-to-diameter ratios between 1:1 and 5:1.
Modern cylindroconical tanks have more than one cooling jacket. This serves two purposes: first, to give the aforementioned optimal thermal movement of the beer during fermentation, and second, to allow the brewer to operate the tank at less than full capacity. A cylindroconical tank will also have a “cleaning device” permanently installed in the top, allowing for easy and automated internal washing of the tank.
Cylindroconical tanks were, from their introduction, well suited for being placed outdoors, thus saving space and building costs for larger breweries. Outside tanks are situated in so-called tank farms, where they are placed very closed to each other. This is made possible by the fact that no manual operations or servicing of the tanks take place in the tank farm itself. Rather, all piping to and from the tanks comes from the tank farm and through an adjacent wall to the beer-processing area inside the brewery. All automatic pumps, valves, or swing arms that need to be operated when using the tanks are placed here, largely eliminating the need for long hoses.
The most modern breweries still use cylindroconical tanks. The next step in process development could be the introduction of continuous fermentation with immobilized yeast. The most recent developments in the technology of these tanks involve what one could call “the accessories” of the tanks in the sense of mechanical mixing (recirculation by pumping from the bottom to the top) of the fermenting beer, as well as advanced control systems that automatically measure and control the progress of the fermentation.
Not all of the traditional tank types have vanished with the introduction of the cylindroconical tank. The requirements of the process involved in brewing traditional English ales have made many large breweries stick to the traditional geometry of square tanks with a “penetrable ceiling,” through which the traditional top-fermenting yeasts will accumulate at the end of primary fermentation and from where the yeast can be automatically harvested by a combination of valves and jets. This type of tank is called “Yorkshire Square,” referring to its shape and the place where they were invented and became widespread during the 20th century. Modern Yorkshire squares can be as large in volume as cylindroconicals and are also closed and fitted with CIP facilities, thus making them just as easy to automate as cylindroconicals. But because they are more complex, they are also expensive in terms of investment, they take up more space, and they cannot normally be placed outdoors.
Many British breweries maintain the tradition of open fermentation. They feel strongly that the method has positive effects on yeast health and beer flavor. In Bavaria, open fermentation is sometimes used in the production of weissbier and occasionally for lager. Many brewers there believe that open fermentation tends to create a more intense aroma profile in weissbier than does closed fermentation.
Marston’s Brewery of Burton-on-Trent, England, is known for having championed the once-common Burton Union system, where fermentation takes place in oak vats and expelled yeast travels between them in open troughs. It remains quite a thing to see, and Marston’s brewers claim that the flavor of their flagship beer would not be the same without it.
University of London, Institute of Historical Research. A history of the county of Middlesex, Vol 2. Oxford, UK: Oxford University Press, 1911. Digitized October 12, 2010.