Fermenting through an Indian summer

Why heat matters so much

Yeast does most of its flavour work in the first two to four days. Warmth speeds it up and changes what it makes. Above the range a strain likes, you get more fruity esters, then harsh fusel alcohols that taste hot and solvent-like and can leave drinkers with a heavy head the next day. Our guide to esters and fusel alcohols explains the chemistry.

Fermentation also makes its own heat. In a vigorous ferment the beer can sit a few degrees above the room. A 20 litre fermenter in a 32 °C room may well be at 35 °C inside during the first couple of days. Most ale yeasts are happiest somewhere around 17 to 21 °C. Lager yeast wants roughly 8 to 13 °C.

Measure the beer, not the room

The first fix costs almost nothing. Tape a thermometer probe to the side of the fermenter and cover it with a folded piece of foam or cloth so it reads the beer and not the air. Stick-on strip thermometers work too, as long as they are not in direct sun or a draught.

Most people who start doing this are surprised. The beer is usually warmer than they thought. The hottest point is day two, not day one.

Cheap ways to keep it cool

• A water bath. Stand the fermenter in a bucket or tub of water. Water holds temperature far better than air. Swap in frozen PET bottles morning and evening. This alone can hold a fermenter several degrees below room temperature.
• An evaporative wrap. Wrap a wet towel or T-shirt round the fermenter, with its end sitting in the water. Then put a fan on it. Evaporation pulls heat out. It works well in dry heat, such as Delhi, Rajasthan or the Deccan in April and May. It does much less in humid coastal cities like Mumbai or Chennai or during the monsoon.
• A spare fridge with a controller. An old single-door fridge with a plug-in temperature controller is the real answer for anyone brewing regularly. It also lets you brew lagers. Our guide to fermentation temperature control at home covers how to set one up.
• The coolest place in the house. An interior bathroom or a floor-level cupboard away from outside walls is often several degrees cooler than a balcony. See our piece on brewing in a small Indian apartment.

Pitch cool and control the first three days

The best single habit is to chill the wort well below your target before pitching. If the yeast starts at 16 °C it will warm up as it works, but it will spend its most important hours in a good range.

After about three days, most of the flavour is set. Letting the beer warm a few degrees at that point usually does no harm. It can even help the yeast finish and clean up. So if you only have enough ice for a short time, use it early.

Brew in the evening, too. Chilling wort with tap water that has sat in a rooftop tank all afternoon is slow and you will struggle to get it cool. Late at night the water is cooler.

Choose yeast that likes the heat

Instead of fighting the weather, some brewers use yeast that wants it. Norwegian kveik strains ferment clean at 30 °C and above, quickly and without the harsh fusels a normal ale yeast would throw at that temperature. Read our guide to kveik yeast for hot climates before you try one.

Saison yeasts also tolerate warmth well. The peppery, fruity character that heat brings out suits the style. Many summer beers in India would be better if they were brewed with these strains rather than a clean American ale yeast at 30 °C.

Plan the year around the weather

Brew your lagers and clean, delicate ales in the cooler months. Keep summer for kveik beers, saisons and anything that hides a little extra fruit. Fill the fridge with a lager in December and it will be ready to drink when the heat arrives.

Understanding why the same recipe tastes different in May and December is the step from following recipes to actually brewing. It is what our fundamentals course is built around.