Fermentation and yeast
Yeast, fermentation, conditioning and lagering. 23 terms.
Aeration
- Getting oxygen into the cooled wort before pitching so the yeast can multiply well: shake it vigorously, pour it from a height or use an aeration pump. Only before fermentation; afterwards oxygen harms the beer.
Airlock
- Small valve in the fermenter lid, filled with water. It lets the CO₂ from fermentation escape but keeps air and germs out. When it stops bubbling, fermentation is not necessarily finished; only the hydrometer tells you that.
Ale and lager yeast
- Ale yeast (ale, wheat beer, Kölsch) ferments at about 15–22 °C (59–72 °F) and gives fruity aromas. Lager yeast (lager, Helles, Pils) ferments cool at about 8–13 °C (46–55 °F) and tastes cleaner.
Brettanomyces
- Wild yeast, “Brett” for short. A fault in most beers but wanted in some styles, such as lambic, Orval or some saisons. It brings barnyard, leather or tropical fruit aromas and ferments very thoroughly, including sugars that normal yeast leaves behind.
Burton Union
- Fermentation system from Burton upon Trent: many wooden casks are connected by pipes to a shared trough. The rising foam carrying the yeast flows into the trough while the beer runs back into the casks. Marston’s still ferments part of its beer this way.
Cold crash
- Chilling the beer hard for 1–3 days after fermentation, to about 0–4 °C (32–39 °F). Yeast and haze settle quickly and the beer clears. Enough yeast still stays in the beer for bottle conditioning. Careful: as it cools, the airlock can suck liquid back into the beer.
Diacetyl rest
- For lagers, raise the temperature to 16–18 °C (61–64 °F) for 2 days at the end of fermentation. The yeast then cleans up diacetyl, which otherwise tastes of butter.
Dry yeast and liquid yeast
- Dry yeast keeps for a long time and is easy to use: sprinkle it on or rehydrate it briefly in water. Usually 50–80 g/hl for ales and 80–120 g/hl for lagers. Liquid yeast comes in more strains but often needs a yeast starter.
Fermentation temperature
- The most important lever for clean beer. Fermentation produces heat itself, so the beer is often 2–3 °C (36–37 °F) warmer than the room. Start at the lower end of the yeast’s range and let it warm up slightly towards the end so the yeast finishes cleanly.
Foeder
- Large oak vat in which beer often matures for years. The foeders of the Rodenbach brewery in Roeselare are famous and fill a whole hall; Flemish red ale matures in them for up to two years.
Forced fermentation test
- Ferment a small sample of wort warm with some yeast, at about 25 °C (77 °F). After 2–3 days it shows the lowest possible final gravity, so you know when fermentation in the fermenter is really finished.
Green beer
- Beer straight after primary fermentation, before it conditions and matures. It often still tastes yeasty, sulphury or of green apple. This disappears as it matures.
Harvesting and reusing yeast
- After fermentation there is a lot of yeast at the bottom of the fermenter. Poured cleanly into a sanitised jar and kept in the fridge, some of it can be used for the next batch within about two weeks. Only reuse yeast from healthy, clean fermentations.
Krausen
- The foamy head on the beer during primary fermentation. It rises during the first days and collapses as fermentation slows. So leave about 20 % headspace in the fermenter.
Kveik
- Traditional farmhouse yeast from Norway. Families passed it down for generations and dried it between brews, once on a carved wooden yeast ring. Kveik ferments very warm, at 30–40 °C (86–104 °F), and very fast, often in two to three days, without the fusel aromas other yeasts produce at such temperatures. That makes it popular with homebrewers who have no fermentation cooling.
Lagering (cold conditioning)
- After fermentation the beer matures cold at 0–4 °C (32–39 °F) for a few weeks. It becomes clearer and smoother; especially important for lagers such as Helles or Pils.
Pitching
- Adding the yeast to the chilled wort.
- The first, vigorous fermentation after pitching. The yeast ferments most of the sugar and krausen forms. It takes about 4–7 days for ales and 7–14 days for lagers.
Pure yeast culture
- Yeast grown from a single cell, which makes it pure and consistent. Emil Christian Hansen produced the first one in 1883 at the Carlsberg Laboratory in Copenhagen, and Carlsberg gave it away free to breweries all over the world. Today almost every brewery uses pure yeast cultures.
Rock cellar
- Storage cellar carved into the rock. Before refrigeration machines existed, lager was stored in cool cellars like these, often with ice cut from lakes and ponds. Kilometres of rock cellars lie beneath the brewery in Pilsen.
Spontaneous fermentation
- Fermentation without added yeast: wild yeasts and bacteria from the air and from the wooden barrels ferment the wort. This is how lambic and gueuze are made in the area around Brussels. Fermentation and maturation often take one to three years.
Yeast
- A single-celled fungus that turns the sugar in the wort into alcohol and carbon dioxide and adds a lot of flavour. Every yeast has its own temperature range.
Yeast starter
- A small batch of wort in which liquid yeast multiplies 1–2 days before brew day, so fermentation starts faster and cleaner.