Fermentation and maturation process of beer production
The brewing process, which is the first phase of the production cycle of beer, is followed by a second phase, called fermentation process, or fermentation. Fermenting wort is a manifestation of metabolism of brewer yeast, which is added after the oxidation to the wort immediately after it is cooled to the fermentation temperature and pumped from the brewhouse to fermentation vessels.
The task of brewer yeast in the fermentation stage is to convert part of the sugars in the wort into alcohol. At the set degree of fermentation the fermentation process is interrupted (not to be the full conversion of 100 % sugar). The so-called young or green beer is pumped into another container, wherein continuing fermentation process has a lower intensity, but at a lower temperature and higher pressure, while the beer carbonated by carbon dioxide. This part of the fermentation process is called maturation of beer, also known as lagering.
Two main fermentation technologies
Design and construction of containers for the main fermentation varies depending on the technology. In our mini-breweries we use both most common fermentation technologies which can be used within one brewery also in combinations and produce beer of different kinds and sensory properties.
I. The bottom fermentation of beer
The style of bottom-fermenting includes all bottom -fermented beers using the yeasts Saccharomyces uvarum. The majority of world production are bottom- fermented beers, including Czech lager Pilsner. These include for example also Dortmunder, Bock, Marzen and more beers called lagers.
Bottom beer fermentation is carried out at temperatures of 6-12 ° C and lasts for 6-12 days. For a month or longer they lie (from here the name “lager”) at subzero temperatures which ensure, among other things, the dispersion of sulfur compounds created during primary fermentation.
The technology of open fermentation in open fermentation vats in the fermentation room is typical mainly for production of bottom- fermented beers. It allows especially convenient collection of krausen from the dead yeast in the last stage of the fermentation which is a prerequisite for making a quality bottom fermented beer of traditional taste. Open technology is absolutely unsuitable for the production of top-fermented beer since the access of air to the active yeast surfaced beer tends to result in the contamination by undesirable organisms.
For small breweries, there is a strong argument for the main beer fermentation in open vats – the great marketing asset. View of the fermenting beer is one of the main attractions for visitors microbrewery.
In modern breweries for bottom fermentation beer mainly use cylindrical-conical tanks. Although the quality of bottom-fermented beer from closed tank does not reach the quality of beer fermenting in open containers, the economic benefit is the decisive reason for the abandonment of traditional fermentation technology.
II. The top fermentation of beer
The style of top fermentation includes all top-fermented beers, usually by yeasts Saccharomyces pastorianus. This includes ales, Porter, Stout, Altbier, Trappist or wheat beer. Top fermentation process is carried out at temperatures of 15-24 ° C and lasts 3-9 days.
In most cases, on the surface of fermenting beer there is a foam caused by rising CO2 together with yeast. That is why they are called top-fermented beers. The fermentation of these beers is usually around three weeks, in some cases it may ferment for several months. Outerwear yeasts are grouped in colonies (they may have a diameter of several meters), live on the surface of wort and are risen by CO2. Higher fermentation temperature causes more floweriness of final beer. Top-fermented beers vary in flavours and we often find exotic aromas (cloves, banana, grep, etc..), although the brewer did not add such ingredients to the beer. All this is caused by the top fermentation.
The best type of fermentation vessels for bottom fermentation are closed cylindroconical tank. The main reason for closed fermentation in tanks is susceptibility of top-fermented beer to contamination yeast foams by foreign organisms from the environment. Another reason is the possibility of controlled fermentation and maturation of beer in one multiplies and easier cleaning and sanitizing closed tanks.
Calculate the size and number of fermentation vessels
1. Calculate the size of fermenters
The main indicator that determines the useful volume of fermentation vessels is planned daily production volume of wort. This means the volume of wort, which we brew for 24 hours in the brewing day. We usualy do not brew every day – at least one day of the week is done sanitation of the brewhouse.
Rule: We choose the next higher volume of fermentation vessels of series depending on the volume of daily batch of wort.
Example: We plan to produce three batches of wort during one brewing day in the brewhouse with volume of 2.5 HL. 3 x 2.5 = 4.5 HL. We need fermentation vessel with a volume of at least 4.5 HL. We do not have the container with a volume of 4.5 HL in the type series, therefore we choose a container with a volume of 5 HL.
The calculated effective volume of fermentation vessels is both for the main fermentation and maturation of beer, since we always fill the entire volume of the fermenter into the maturation vessel.
2. Calculate the number of fermenters
Among the indicators that determine the number of fermentation tanks for primary fermentation, there are the time of main fermentation of the daily batch of wort,and a number of brewing days that will take place during this time .
Rule : The number of containers for the main fermentation must be at least as high as how many days the brewing takes place during one period of the main fermentation . The types of fermentation vessels are chosen according to the type of fermentation of selected beers (CC tanks or open fermentation vats for bottom -fermented beers or CC tanks then only for top-fermented beers).
Example : We plan to produce 1x weekly top-fermented beer with main fermentation time 6 days and twice a week bottom-fermented beer with main fermentation time of 12 days. It follows that in the first beer during 6 days it is held up only one brewing day and we need for it one fermenter of the type cylindroconical tank (CCT) . In contrast, while making the second beer there are four brewing days during 12 days, so we need 4 fermentation vessels, either cylidroconical tanks (CCT), or open fermentation vats (OFV). Altogether our brewery needs 5 fermentation vessels for main fermentation with the volume coounted according the previous text. The structure of the vessels will be 1 OFV + 4 CCTs or 5 CCTs.
Note: The recommended duration of fermentation is the main part of each recipe for a selected type of beer. Yet the real time of the main fermentation vary up to + / – 2 days, which is due to a number of factors, such as vitality of the yeast, the quality of malt, wort extract variable, temperature and others. In fact, for each batch the brewer decides on the termination of the main fermentation according to measurement results of fermented extract by hydrometer. For the above reasons, we recommend calculating the time of the main fermentation by two days longer than the recipe states. In practice, this usually means having one more fermentation container in the brewery. Ignoring this recommendation will result in a lack of fermentation containers and non-standard extension of the main fermentation of the problematic batch and reducing the planned production volume.
Technical parameters of the fermentation vessels for primary fermentation of beer
Calculate number and type of vessels for beer maturation
Among the indicators that determine the number, size and type of containers for beer maturation, there are the recommended maturation periods (lying) of produced beer, the brewing daily volume of wort and the number of days that takes place during this period.
Rule: The number of containers for beer maturation must be at least as high as how many batches mature at the same time.
The type and shape of maturation vessels is not very important, but they must be able to keep the maturation beer under the set pressure using a barrier facility. They are cylindroconical tanks, vertical maturation cylindrical tanks and horizontal maturation tanks. Beer can further mature in service tanks. All these tanks are different types of beer production tanks, which are used in three phases of the beer production cycle.
Example : We plan to produce once a week top-fermented beer with a suggested maturation period of 3 weeks and twice a week bottom- fermented beer with a recommended period of maturation nine weeks. It means that the first beer needs for simultaneous maturation of batches 3 maturation vessels, the other beer 18 maturation containers (2 x 9). Total need in the brewery is 3 +18 = 21 maturation vessels.
Note : For specialy beers with EPM > 12 % it is recommended to have beer maturation time of several months. To equip the brewery with maturation vessels for example for one batch of 14 -degree beer a week implies the need for extremely high amounts of maturation tanks in the brewery. This is not normally needed because the demand for strong beers in restaurants is usually not that big. In practice this extreme is solved in winter, when beer consumption with a lower alcohol content declines, the maturation tanks reserved for the basic assortment can be used (brewing schedule is temporarily reduced to the half of production volume) to produce special beers with higher alcohol content, while the maturation process takes place in tanks only as long as necessary for a few weeks, when it is not needed to use them for the usual summer assortment. Special beer is filled into kegs stored in cold, where maturation process continues. Due to the long lifetime of beers with more alcohol it is possible to offer these winter specials from kegs during all remainder of the year, when the tank is used for production of usual assortment of weaker beers.
Technical parameters of vessels for maturation (fermentation) of beer:
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