Brewing a lager at home

What changes

The yeast: twice as much

At 10 °C, yeast multiplies slowly; if you pitch too little, it takes days to start, bacteria take advantage and it produces more unwanted compounds (sulphur, acetaldehyde, diacetyl). The brewers' rule: 1.5 million cells per millilitre and per degree Plato for a lager, against 0.75 for an ale. For 20 litres at 1.050 (12.4 °P): about 370 billion cells, i.e. two 11 g sachets of dry yeast, or a 2 to 3 litre starter from one pack of liquid yeast (the yeast pitching rate tool and the yeast starter tool do the maths). Modern dry lager yeasts are reliable and simple; rehydration according to the instructions matters more than for an ale.

Fermentation

• Chill the wort down to fermentation temperature, 10 to 12 °C, before pitching. Pitching at 20 °C "to get it started" then chilling is a classic cause of esters and sulphur. If you cannot get any lower, pitch at 14-15 °C and chill within the first hours.
• Oxygenate the wort well: cold and with a lot of yeast, the need is greater than for an ale; shake the closed fermenter vigorously for several minutes.
• Hold 9 to 13 °C for 10 to 14 days. Activity is slow and quiet: no spectacular krausen, and a normal sulphur smell.
• Diacetyl rest: when the gravity is 2 to 4 points from the expected final gravity (for example 1.016 for a final gravity of 1.012), let it rise to 17-18 °C for 2 to 3 days. The yeast finishes fermentation and reabsorbs the diacetyl. Without this rest, the lager smells of butter, the most frequent fault of homemade lagers (see off-flavours).
• Check that the final gravity is stable over two readings, then chill.

Lagering

The word lager comes from the German for "to store". At 0-4 °C for 3 to 8 weeks, the yeast and the haze drop, the sulphur evaporates, the flavours blend. You can do it:

• In the fermenter, before bottling: the beer is brilliant at racking, but little yeast is left for refermentation; add a pinch of dry yeast at priming.
• In the bottle, after refermentation: 3 weeks at 20 °C to take on the gas, then the bottles in the cold for the lagering. Simpler for anyone with only one cold space.
• In a keg, under pressure: the most practical method when you have one.

Without a cellar or a dedicated fridge

• Winter: an unheated room, a garage, a larder, a stairwell often hold 8 to 14 °C from December to February. A min-max memory thermometer placed there a week ahead tells you whether the spot is suitable. It is the traditional season for lagers.
• A water bath: the fermenter in a large tub of water, with frozen water bottles changed morning and evening, holds 10-12 °C in a room at 18 °C and smooths out variations.
• "Lager at ale temperature" yeasts: some dry strains give a clean beer at 15-18 °C, and a few kveik or hybrid strains imitate a lager at 20 °C (see brewing with a kveik). The result is not a lager in the strict sense, but a crisp, ester-free beer that comes very close.

Fermenting under pressure

Another way, with no cold: ferment in a closed vessel fitted with a valve set at 0.8-1 bar. The CO2 that stays dissolved slows the yeast's multiplication, so it produces fewer esters; a lager yeast kept at 15-18 °C gives a beer close to a classic lager, and lagering is done under the same pressure. The beer is carbonated in the fermenter and ready in three to four weeks instead of eight to twelve. You need a fermenter designed for pressure, with a safety valve and a gauge, the same yeast dose, the first day without pressure, and less priming sugar if you bottle. Settings, safety and a schedule are detailed in fermenting under pressure.

The recipe: simple

A lager is brewed with few ingredients and judged on execution. For a 20-litre German pils: 4.2 kg of pilsner malt for a gravity of 1.048 at 72 % efficiency; mash at 63 °C for 30 minutes then 70 °C for 30 minutes, or a single rest at 65 °C for a drier beer; a 90-minute boil because of the DMS of pilsner malt (see off-flavours); noble hops (Hallertau, Tettnang, Saaz, Perle) for 30 to 38 IBU with an aroma addition at the end of the boil; low-alkalinity water, little sulphate (see brewing water); final gravity 1.010, 5 % alcohol. The bounds of each lager style are in the list of styles.

Timetable for a 20-litre pils

Common mistakes

• A single sachet of yeast: slow start, sulphur and acetaldehyde.
• No diacetyl rest: butter.
• Pitching warm then chilling: esters, a lager that tastes of ale.
• A 60-minute boil with pilsner malt and a lid on: cooked corn.
• Bottling after a long cold conditioning without adding yeast: flat beer (see flat beer).
• Impatience: a lager tasted at four weeks is a bad lager; the same one at ten weeks is good.