Wort aeration or olive oil? It is an interesting and, for some, wacky concept but using olive oil instead of wort aeration has been utilised by both professional and home brewers for a number of years. However for many brewers, and this includes home brewers, using the olive oil method goes against the grain as it flies in the face of traditional brewing dogma. Therefore in the interests of brewing science and, just because we thought it would be fun, we have had a look at the brewing literature to identify whether wort aeration or olive oil is better.
What is Wort Aeration and Why use Olive Oil?
During the early stages of fermentation the yeast population goes through a period of rapid growth which requires sterols and fatty acids for the synthesis of healthy cell walls. The normal process for the yeast cell to achieve this cell wall growth is through a biochemical pathway which requires the presence of oxygen. Thus brewers will energetically aerate their wort to encourage yeast growth and this in turn leads to a vigorous and healthy fermentation. However, some brewers are paranoid about introducing oxygen at any stage of the brewing process as they believe it will result in a stale oxidised flavour in the final beer. By using olive oil it is suggested that there is no need to oxygenate the wort as the requirement for fatty acids is provided by the olive oil. By removing the need for aeration it is argued that the beer brewed has a cleaner fresher flavour as it has not been oxidised. Opponents of the technique argue that the drawback in using olive oil is the potential reduction in foam stability as any lipid remaining in the final beer would act in a destabilising way.
The most in-depth and interesting research that we have found examining the technique was conducted by Grady Hull, brewer at the New Belgium Brewing Company. Interestingly the results from his work suggest that olive oil can be used instead of the traditional wort aeration process. In his trials he found that, when using olive oil, the fermentations were slightly longer but the beers produced had comparable foam properties when compared to traditionally brewed beers. He also found that the ester profile of the beers brewed with olive oil was significantly higher than the controls and the flavour stability was significantly improved. The research looks to support the technique which all bodes well for olive oil. Would we recommend employing olive oil in your home brewing? Well it certainly takes a brave home brewer to try it but if the science is to be believed it could be worth trialling it on a batch or two. However, as a home brewer how do you go about reproducing this technique on a small scale?
How and when do you add olive oil during home brewing?
There is not an awful lot of information that we could find about specific techniques for the home brewer to employ. Therefore we have come up with a few guidelines that we have started to test out.
First thing to remember is don’t just add a teaspoon or two of your finest extra virgin olive oil directly to the fermenter. This unfortunately is not a very good way of going about adding olive oil as it is immiscible in water, will not mix into the wort and will tend to stick to the side of the fermenter giving an ugly oil slick effect and give you no real benefit. In the New Belgium experiment Grady Hull added olive oil to yeast that was being stored prior to pitching. We have tried to replicate this by adding a 6 g sachet of yeast to a small sample of wort and then adding a single drop of olive oil from a pippette. We then left this yeast culture to stand with the occasional shake to encourage the yeast to mix with the oil. Once we saw the yeast showing signs of life we pitched into the fermenter as normal and waited for fermentation to kick off. By pre-conditioning the yeast in this way the oil interacts with the cell wall and so is absorbed more readily and should give better results. Well that is the theory. We are currently waiting for the results from the first beer brewed using this technique so will report back in due course but the fermentation appeared to be vigorous so fingers crossed. For the moment the for us the jury is out over the decision of wort aeration or olive oil.