If you’re encountering some flavours in your beer that are a little on the nose, there’s a good chance unhappy yeast could be to blame. Sour, sulphurous, solvent and yeasty flavours, along with the unwanted presence of diacetyl and acetaldehyde and unplanned esters can all result from unhealthy yeast.
So, how do we ensure that the yeast we’re relying on is fit for purpose and in good health? The best place to start is with the basics. This article will outline three key areas to pay special attention to when brewing. If you do, there’s a good chance you’ll avoid or minimise any undesirable flavours.
To help you ensure your yeast is given the best chance to perform as desired, here are three key areas to focus on…
1. Temperature
Different yeast strains have different temperature ranges in which they function best. If the temperature of your wort is too low, the rate at which the cells metabolise the sugars will slow and ultimately you’ll risk a stuck fermentation. If the temperature is too high, the fermentation process can contribute undesirable flavours to your beer. These are most commonly in the form of esters and fusel alcohol. Esters add a fruitiness that is desirable in some styles – think Saisons and farmhouse ales – but are typically unwanted. Fusel alcohols, when present in large amounts, add a flavour often likened to paint thinners. If you’re brewing with Bluestone Liquid Yeast, be sure to refer to our website or packaging for information on the desired fermentation temperature.
A key moment in the fermentation process is the pitch, and it’s important here to ensure you’re wort is within the correct temperature range. Your yeast will be most active over the first 48 hours of the fermentation, and it’s during this phase that the most damage can occur.
While it’s best to avoid any off-flavours developing in the first place, leaving your brew to mature for a week or two after fermentation can help as the yeast will clean up some of these off-flavours.
2. Oxygen
Before pitching your yeast ensure that your wort is sufficiently aerated. Oxygen is a key ingredient in the process whereby yeast converts the sugars in your beer to alcohol and carbon dioxide. It also ensures your yeast cells grow and reproduce during fermentation. Yeast that is struggling to grow and reproduce can become stressed and stressed yeast can lead to off-flavours and poor attenuation.
3. Cell count
Like Goldilocks, your beer will be happier if the cell count of your pitch is ‘just right’. If you under-pitch, your yeast may over-compensate and begin reproducing too fast. This can produce off-flavours like sulphur, fusel alcohol, diacetyl, and unwanted esters. There’s also a risk that if gravities get too high, you’ll find yourself with a stuck fermentation.
On the other hand, if you over-pitch, your fermentation can be over before your beer has had a chance to take on certain important characteristics, such as body and flavour complexity. There is also a risk of autolysis, which will leave your beer with an unpleasant ‘yeasty’ flavour.
While you’re more likely to develop unpleasant flavours from underpitching, you can always pitch a little more yeast to rectify the problem. Over-pitching, however, is not something you can correct.
