Fermentation Parameters

There are hundreds of different yeast strains available, when you select one yeast instead of another; it’s often based on the flavour profile which you’re expecting. Many yeast strains ferment in a clean manner, making no significant flavour contributions; this allows the malt and hops to shine, whilst various other yeasts contribute hugely to both the flavour and aroma of the beer. If you want to obtain a contribution from the yeast, you need to provide the best environment that you can.

A Little Too Much Activity

It is possible to encounter a particularly vigorous fermentation which pushes the stopper out of the fermentation vessel. Following the stopper, the yeast and krausen follow, leaving quite a mess. This whole situation can be avoided by using a blow-off tube. A blow-off tube is merely a large diameter tube which fits tightly into the fermenter. The other end is put into a bucket of water or sanitizer, this forms an airlock. Gas can leave the fermenter, but no air can enter and any yeast which finds its way out ends up in the bucket.

Burst Fermenter

Pitching Rates

One of the easiest things that a homebrewer can do to increase the quality of their beer is to ensure that a suitable amount of yeast is being pitched. Numerous flavour compounds are produced through the growth phase. When the yeast is initially pitched, it starts taking up oxygen and vital nutrients which are present in the wort and will multiply until these nutrients have been exhausted. If you begin this process with only a small number of yeast cells, they need to reproduce more times than if you start with a large number of yeast cells. As the yeast multiplies, it is generates various flavour compounds. Low pitching rates are associated with increased levels of esters, diacetyl, acetaldehyde, and low attenuation. In addition to this, there are concerns with contamination, as a low pitching rate increases the likelihood of unwanted bacteria out-competing the yeast, generating unwanted flavours.

It is also possible to over-pitch the yeast; this is associated with lower than desired levels of flavour compounds and aromatics. Whilst it is generally considered to be better to over-pitch than under-pitch, you should be aiming to do neither. To calculate the amount of yeast to pitch for a 5-gallon batch of beer, we recommend that you use the following equations to calculate a rough estimate. SG is the last two points on your specific gravity reading. We have included two equations, one is for ale yeast, whilst the other should be used for lager yeasts, as you can see, lager yeasts usually require around twice as much yeast than ale strains.

Ales : 3.6 × SG = Yeast Cells in Billions

Lagers : 7.2 × SG = Yeast Cells in Billions

For instance, if you were brewing an ale which was to have a starting specific gravity of 1.048, you would times 3.6 by 48, giving you a number of 173 billion, which is the number of yeast cells you require.

Major suppliers of liquid yeast sell packets which contain around 100 billion cells; the suppliers claim that this is appropriate for wort with gravities up to 1.060. This number is significantly lower than what we calculated earlier, the suppliers claim that a fresh packet of their yeast, with all yeast cells being viable will be sufficient. Whereas our calculation assumes that some cells will not be viable. Moreover, wort with a gravity above 1.060 is said to be a high-gravity wort which puts a large amount of stress on the yeast. Therefore, at these specific gravities, correct pitch count is much more important because the yeast is going to struggle in such environments.

Regardless, it is always a good idea to create a yeast starter. This increases the amount of yeast that is pitched, as well as making sure that as many yeast cells as possible are viable. There are instructions here which detail how to make a starter. To determine the volume of starter that is required, you can find a number of excellent online calculators, we recommend www.mrmalty.com.

Temperature Control

Temperature control is hugely important, arguably more so than even pitching rate. Low fermentation temperatures are associated with low attenuation and even worse, stuck fermentations. Conversely, high fermentation temperatures are associated with the production of fusel alcohols throughout the lag phase aswel as increased ester generation during active fermentation.

Optimal fermentation temperatures differ between yeast strains but in general, ale yeasts will ferment well between 62-72 degrees Fahrenheit, most homebrewers aim for a temperature in the middle. Higher temperatures will create more esters, whilst a lower temperature creates a cleaner tasting beer. As mentioned earlier, specific strains have optimal temperatures which differ from this average, therefore it’s important to look at the manufacturers recommendations. Commonly, yeast strains originating from Britain, which usually create more esters, tend to prefer higher temperatures, whereas German yeast strains tend to prefer lower temperatures.

Lager strains usually need cooler fermentation temperatures, with an average fermentation range of 48-58 degrees Fahrenheit. This cooler temperature range creates a beer with a cleaner taste, as lower levels of esters are produced. Just like ale strains, the optimal temperature differs between different strains and the manufacturer’s instructions should always be consulted.

It is also worth keeping in mind that fermentation is an exothermic reaction, meaning that as the yeast gets to work, heat is produced. As such the wort will increase by around 5 degrees, compared to the surrounding temperature.

There are various techniques to regulate the temperature of the beer; some require modern tech, whilst others involve absolutely none. Before modern times, beer was brewed with the seasons in order to take advantage of the weather, this is certainly still possible depending on where you live, but it limits your brewing to particular times of the year.

Subject to your local climate, you will need to either keep your fermenting beer warm or cool it down. Without a doubt, keeping your beer warm is the easier option. There is a large range of products which can be used to keep the fermenter warm, such as electric blankets which can be wrapped around the fermenter. A really good and cheap way to keep the fermenter at a stable temperature is to place it in a large bin filled with water and then use an aquarium heater to keep it warm. These aquarium heaters often have a built-in thermostat, but they can be inaccurate so it’s worth using a backup thermostat. The sheer volume of water in the bin protects against temperature swings.

Alternatively, if you’re going to cool down your fermenter there are again, various options. Once again, putting the fermenter into a bin full of water will protect against temperature swings. And bottles of ice can then be inserted to decrease the temperature. Another good option is to construct a box out of Styrofoam insulation to hold the fermenter and add ice bottles when required; ice is an effective way of cooling down the fermenter and should definitely be considered. As the ice bottles lower the ambient air temperature in the box, the fermenter will be cooled. You can find many different designs online, with some containing multiple compartments with fans to blow the cold air onto the fermenter.

Alternatively, you can use a chest freezer with an external thermostat. Chest freezers are easy to find used and can often be cheap choice. These systems often require a large space requirement, but allows for precision temperature control which is great for both ale and lager fermentation, but can also be used for cold crashing and long-term lagering as well.