Most sachets of home brew ale yeast have a fermentation temperature range on the label like (12-25°C). But, unless you are brewing a beer style that warrants it (like a “Saison”) the general rule of thumb is to ferment below 20°C Ideally, 15 – 19°C is best. (Fermenting ale yeasts at temperatures lower than 15°C can also lead to slow and even stalled fermentations).
So how do you home brew in summer?
The first and simplest method is to find a spot in your house where the temperature is in this range.
If this isn’t possible then the next option is to immerse your fermenter in a larger vessel of water. Find a watertight container that is larger than your fermenter – a bath, plastic storage box or large washtub.
Put your fermenter into the chosen container and fill it with water to the same level as the beer in the fermenter. Drape a towel or t-shirt over the fermenter so that it wicks-up the water.
This results in cooling by evaporation. You will need to monitor the water level during very hot periods and may need to top it up occasionally.
To maintain an even temperature, you may want to freeze some water filled 2 litre plastic bottles and place them in the water. Always keep 4 frozen and add 2, changing the bottles over each morning and night will allow you to keep a constant temperature for the fermentation.
Using this simple technique, you can brew beer during summer and achieve satisfactory fermentation results.