The technique involved has remained practically unaltered for centuries. The equipment has changed (stainless steel now), temperature control of the vats and cellars has been improved and greater care is taken over hygiene.
Process times have stayed the same though: a working day of around 8 hours for a modern brew is not so different from that of an old fashioned one. The phases in the brewing of beer are milling, mashing and saccharification, filtration, boiling and hopping, cooling and aeration, fermentation, bottling and refermentation. Let’s look at these eight phases in detail.
The grains of barley malt and any other cereals used are milled to extract their starch content. This is a vitally important operation in that incorrect milling may cause various problems in the subsequent production phases or undesired organoleptic characteristics in the finished beer.
In the mashing phase the milled malt is mixed with hot water to activate the enzymes in the malt. These enzymes require certain temperature and acidity conditions. There are two mashing methods:
a) infusion: the water/cereal mix is gradually raised to given levels of temperature by heating;
b) decoction: part of the mix is separated and boiled and then returned to the main mix. Infusion and decoction give beers different characteristics.
There are various enzymes in malt, each with a different action, and they work most effectively at different temperatures and acidity levels (pH). The most important ones are in the amylase group, which break down cereal starches into simple sugars. Mashing and saccharification therefore form a fundamental phase in production because this is when the brewer determines the desired basic characteristics of the finished product: body, drinkability, head retention, etc.
When saccharification is completed, i.e. when the starches have been turned into simple sugars, the mash must be filtered. This is usually done in a vat with a double bottom which holds back the draff (residues) and enables the sweet wort to be filtered till it’s free from impurities. To make this action even more effective, the first wort (cloudier) is recirculated through the filter vat for further filtering. After the first wort is extracted there is still a considerable amount of sugars caught in the draff. To recover these and increase the efficiency of the production system hot water is poured onto the draff two or three times and new wort is recovered in the subsequent filtering phases. Filtration is important because it prevents barley malt husks and other impurities getting into the wort and the subsequent boiling phases, which would cause the release of tannins and other substances into the finished beer, in turn causing undesired sour flavours.
After filtration the wort is boiled, usually for 60 to 90 minutes. Boiling performs various functions:
– it kills any enzymes still present;
– sterilizes the wort;
– concentrates it by evaporation and favors, in certain styles of beer, the creation of “Maillard compounds”, which produce notes of caramel and breadcrust.
Depending on the hops introduced during the process, boiling also facilitates the coagulation and precipitation of proteins and polyphenols and, if prolonged, enables the transformation of the alpha acids in hops into the iso-alpha acids that give beer its bitter tang.
In organoleptic terms, hops produce not only bitterness and but also aromatic notes thanks to their essential oils. As already mentioned, the “bitter” function is only possible if the wort is boiled or in any case at temperatures over 96° C; otherwise the isomerization of the alpha acids is not effective.
After boiling, the wort contains various “impurities” in the form of hops residues and coagulated proteins. The commonest way to eliminate these is the “whirlpool” system, in which the circular movement of the wort causes the solid parts to decant in the central area of the vat in which the wort is temporarily held. The wort is then cooled in a heat exchanger to the temperature required for the chosen type of fermentation (high = 16-25° C; low = 7-15° C) and then transferred to the fermentation tanks.
Since the wort has a low oxygen content after boiling and oxygen is indispensable for the multiplication of the yeast mass, brewers use various methods to the replenish the necessary oxygen, such as blowing pure oxygen or sterile air into the wort or simple mechanical aeration (eg. by pouring the wort into the fermenter from a certain height or simple stirring the wort in the fermenter). The wort is finally ready for the addition of yeast and the fermentation phase.
Fermentation occurs at temperatures between 18 and 22° C and lasts from 4 to 7 days. The vat must be well sealed to protect the wort against external agents. A few hours after the yeast is added the wort starts to “fizz” and produce a thick and increasingly heavy foam. This normally occurs from 5 to 15 hours after the addition of the yeast (depending on the type used). 24 hours after the addition of the yeast, the foam is removed, taking care to also remove all the particles of spent yeast and not let them fall back into the wort. This operation is repeated after another 24 hours. The final density is around a quarter of the initial value. After resting the liquid for a couple of days to reduce cloudiness, the beer is ready for the next phase.
After dissolving 6 or 7 grams of sugar per liter of beer in half a liter of water and after boiling and cooling it, the beer is decanted to another suitably sized container. Care is taken not to include the yeast deposited on the bottom. Sugared water is then poured into the beer and the whole is slowly stirred. The product is then bottled leaving 3-4 cm of air between the beer and the cap in the case of 33 cl bottles (and proportionally for other sizes).
The bottles are then left in a fairly warm place (20-25° C) for a week before being moved to a cooler ambience out of the light. The addition of sugar for secondary fermentation in the bottle will produce the beer’s carbonation (fizziness). Malt extract or wort may be added instead of sugar. After 1 or 2 weeks the beer will already be clear, with yeast sediment on the bottom, but must mature further before becoming good: from 3-4 weeks to 2 months for light beers, 3 months for medium beers and up to 1 year for “strong” beers. The brewer may decide not to filter the beer, so that the yeast (which in any case remains in suspension) passes into the bottle for secondary fermentation. Alternatively, 3/4 of the beer, or all of it, can be filtered, after which yeast is re-added for refermentation.