For many homebrewers, temperature controlled fermentation is something they consider when all other elements of their homebrewery have been put together. Arguably though, fermentation control may be one of the most important things you can do to improve your results. Yeast are responsible for so many flavour compounds in beer that just by being able to hold your beer at the optimal fermentation temperatures for your yeast strain should result in a noticeable improvement to your finished beer.
If you still aren’t convinced, we’ve compiled a list of the top ten reasons you should consider adding temperature control to your homebrewery setup;
1. Fermenting above the recommended fermentation temperature may result in unwanted esters from the yeast or even harsh fusel alcohols which can make your beer taste ‘hot’. Fusel is the German for ‘bad liquor’ and the term ‘fusel alcohol’ refers to alcohols that contain more than two carbons. Although there is no definitive proof many people feel that high levels of fusel alcohols can contribute to hangovers.
Esters are a secondary product produced as a natural part of fermentation and are desirable to varying degrees in most beer styles. As temperature increases the concentration of esters produced will also increase. A temperature increase of 15°C can result in an increase in esters of up to 75% so temperature control is vital if you are hoping to have any control over the final flavour profile of your beer.
2. Fermenting below the recommended fermentation temperature may result in slow or stopped fermentation which leaves your beer susceptible to infection. Fermenting cold will also limit the production of esters which can result in a beer that is lacking flavour
3. Fermentation is a reaction which generates heat so even if you chill your beer well and pitch at an ideal temperature, the temperature inside your fermenter will rise and this can lead to unwanted flavours being produced. If you are able to cool your fermenter you can control this rise in temperature and limit any negative impact this will have.
4. Keeping your beers at cold temperatures for an extended period of time is one of the best ways to clear your beer and produce good looking beers. Low temperatures promote ‘flocculation’ which refers to the tendency of brewers yeast to clump together and drop out of suspension in the fermenter. If you are able to control your fermentation temperatures you can include a ‘cold crash’ step in your fermentation profile. Cold crashing is when brewers lower the temperature of their beer to as close to freezing as they can. This causes solids within the beer to drop to the bottom of the fermenter and results in a much cleaner looking beer. Cold crashing can also help to minimise chill haze.
5. Fermenting at a higher temperature can cause your yeast to grow too quickly and run out of nutrients before it finishes consuming the sugar in the wort, leading to an incomplete fermentation.
6. At warmer temperatures yeast cells can start to become stressed and die, leaving less cells to do the work which can result in poor fermentation and off flavours. If the yeast cannot complete fermentation this can leave you with a lot of unfermented sugars in your beer, resulting in a sweeter final beer.
7. Some ales are supposed to have fruity esters and yeast character that comes from fermenting towards their top end. Fermenting too cold restricts the production of these flavour compounds, resulting in a beer that is not to style. If you rely on ambient temperatures for your fermentation you will have very little input when it comes to recreating your beer as different levels of esters will be produced at different temperatures. This can result in two beers, using the same ingredients and otherwise similar process, tasting very different to one another. By properly controlling your fermentation temperatures you have more control and therefore better chance at repeatability.
8. Less CO2 escapes from solution when fermenting at cold temperatures meaning flavour compounds that would typically be ‘scrubbed off’ are left in the beer. This can be useful for several reasons. If you dry hop your beer during active fermentation you may choose to lower the temperature of fermentation slightly whilst the hops are in contact with your wort to avoid the delicate hop aroma being removed by escaping CO2. On the other hand, if you have started fermentation towards the colder end you may choose to gently raise the temperature in order to remove any off flavours and aromas, such as sulphur aromas which can occur.
9. The ability to control your temperature allows you to consistently replicate your beers across different batches.
10. Being able to control your fermentation means that you are not restricted to seasonal brewing (ie. Having to brew ales in the summer and lagers in the winter). You can produce all styles, all year round with greater consistency.