Why use olive oil in your homebrew?
Your yeast need oxygen for a happy and healthy fermentation. Yeast use oxygen during the lag phase to synthesize sterols and unsaturated fatty acids for its cell walls. If there is not enough oxygen, the yeast can not grow and die off early. Low oxygen leads to stalled fermentations and off-flavors. This is the reason you need to shake the carboy before pitching your yeast.
The problem is with too much oxygen your wort can become oxidized. An oxidized beer will taste like cardboard ass (or sherry but not in a good way). Any time you add oxygen to your beer, you run the risk of some oxidation. The olive oil solution is an attempt to avoid oxidation.
So why would you add olive oil? The idea behind olive oil is instead of giving the yeast oxygen to manufacture the unsaturated fatty acids, give the yeast an unsaturated fatty acid. Your wort doesn’t get oxidized and your yeast get what they need for their growth.
- Oxygen is used by yeast to synthesize sterols and unsaturated fatty acids for its cell walls
- Ale yeasts need about 5 parts oxygen per million in wort, while lagers can need 10 to 12 parts oxygen per million.
- Olive oil gives yeast the compounds synthesized for cell wall construction
Where did this crazy idea come from?
Adding unsaturated fatty acids like linoleic acid to wort was attempted in several studies, but in 2005 Grady Hull, with the help of New Belgium Brewery, decided to try using olive oil. Olive oil was chosen because it is much more readily available and olive oil contains the same unsaturated fatty acid beer yeast produce. Linoleic acid is not naturally produced by yeast. It would seem olive oil was the perfect choice.
- The olive oil experiment was in a 2005 thesis by Grady Hull
- The experiment was conducted at New Belgium Brewery in Fort Collins, Colorado
How well did it work?
The experiment worked quite well for Grady Hull’s goals. The original goal was to compare the effects of adding olive oil to storage yeast vs. traditional wort aeration. They found they could achieve similar results in the final product using olive oil. The paper did note ester production was higher than the traditional aeration beer, but the additional esters were within production limits; in fact the flavor panel at New Belgium preferred the higher ester flavored beer. They also found the fermentation times were slower.
The New Belgian Brewery was also looking to increase shelf life for their beers. Less oxygen means they can keep their beers on the shelf longer. Hull reported increased flavor stability in the olive oil beer. Based on the goals set out by Hull, the experiment seemed to hit a home run for macro breweries, but the question everyone wanted to know still remains. How well would olive oil work on my homebrew? No one really knows yet.
- The olive oil beer produced more esters and took longer to ferment – both were still within accepted norms
How much olive oil do I use in my homebrew?
In the study, Hull added olive oil based on the total number of cells. He didn’t list actual volumes in the paper because there can be variations in yeast slurry thickness. In the first trial they added 1 mg of olive oil per 67 billion cells pitched into 360 hl of wort, and the final trial they added 1 mg per 25 billion cells pitched into 2100 hl of wort.
So how much olive oil is this on a homebrew scale? Going by their numbers you would need about 0.036 ml in your starter for a 5 gallon batch. In short, less than a drop. Probably not even that much. Most brewers adding olive oil in their homebrew are sticking a pin tip into olive oil and rinsing it into their wort. Even this small amount is likely too much if the numbers are correct.
The study’s authors added their olive oil to the yeast slurry about 5 hours before use. To do this at home, you need to add the olive oil to your yeast starter.
- Use the tip of a pin to get a small drop of olive oil
- Add the olive oil to your starter
Questions left unanswered
The first question I had after reading the thesis is: would this work for lagers? The study reported higher esters in each of their trials, but since they were making Belgian ale the esters were desired. In the case of a lager, you do not want increased ester production. This technique would be good for big beers or ales where esters are expected, but I have to question how well it will work in lagers.
Many homebrewers in brewing forums using this method and claim wild fermentations, wonderful beers, etc… but unfortunately this is anecdotal evidence. The study at New Belgian Brewery claimed their olive oil fermentations actually took 20% longer than normal fermentations. If this is accurate, your fermentation at home should be slower not faster. It would be interesting to devise an experiment to try at home to see how well this scales to homebrew breweries. If you’ve tried this before, let me know how well it worked for you in the comments below.
- Interesting idea, but it needs more experimentation for home use
- Increased esters might be bad for a lager