It is well known that yeast need oxygen in order to synthesize sterols and unsaturated fatty acids for healthy cell walls. Typically this is accomplished by saturating with oxygen using pure oxygen and an oxygen stone prior to pitching the yeast or, inefficiently by periodically swirling the fermentation carboy after pitching the yeast. However, notes in the literature have documented that the addition of linoleic acid1 (and unsaturated fatty acid) or olive oil2 to the yeast can accomplish the same result in the absence of oxygen and that this also improves flavor because the beer does not suffer as much oxidation. Now there is a lot of unsubstantiated speculation in the home brewing community that the addition of olive oil kills the head formed upon pouring a beer. I have been using this olive oil addition method in my brewing for a year and I have seen no problem with formation and maintenance of foam head.
I wanted to do a side by side comparison between the oxygen infusion method and the addition of olive oil, focusing particular attention on the measurement of head formation and retention. It was not my intent to replicate work that had already been reported, but rather to dispel rumors that olive oil addition kills head formation and retention.
Materials and Methods
Two one-gallon jugs were filled about 2/3 full with the same wort. One wort sample was oxygenated and pitched with yeast. The second relatively oxygen free wort sample was pitched with yeast and olive oil. Of course I used the same rehydrated yeast and amount of yeast in both samples. I then fermented these under identical conditions, bottled, and evaluated for head retention and flavor.
|Water||1/2 cup sterile tap water||1/2 cup sterile tap water|
|Yeast||1.5 g SafAle-04 British Ale yeast||1.5 g SafAle-04 British Ale yeast|
|Wort||3 liters Rainbow Irish Red wort||3 liters Rainbow Irish Red wort|
|Olive Oil||nothing||one drop olive oil|
|Oxygen||Oxygenate via stone for 1 minute||nothing|
For each 3 liter wort sample, 1.5 g dry (equivalent to 1 package per 5 gallons) SafAle-04 British Ale yeast was hydrated using one-half cup warm sterile tap water. Dry yeast was used because it is easy to measure quantitatively in order to insure the same number of yeast cells were added to each wort sample. One drop of olive oil was added to one sample of hydrated yeast and shaken periodically over a 20 minute period before pitching into the oxygen deficient wort. It should be noted that this is approximately 3-5 times as much olive oil as I usually use for this purpose because it was difficult to reproducibly add only one third of a drop of oil. Normally I add 2 drops of olive oil to yeast for 5 gallons of wort. The control sample of wort was oxygenated for2 minutes using pure oxygen with an oxygen stone. Both samples were fermented under identical conditions.
The temperature profiles of each test sample were the same (figure 1) during fermentation. The specific gravity of both samples vs. time (figure 2) was also roughly the same. Observations during fermentation also indicated that the krausen formation was approximately the same for both samples (figures 3 - 6). There was no significant difference between either sample by subjective flavor comparison. There was a slight decrease in the head retention such that the head was comparatively reduced by half in the olive oil inoculated sample compared to the oxygen inoculated sample (figures 6 -12).
While the lesser head retention is significant, this result may be due to the 3-5 times larger amount of olive oil used in this experiment compared the usual procedure for 5 gallons. However, even this large amount of olive oil still yielded a good head upon pouring that lasted for the first several minutes of beer consumption. Perhaps this is a fair trade off for having healthy yeast growth without the need for oxygen infusion equipment. The next step would be to repeat this experiment using a reduced amount of olive oil, perhaps by diluting some olive oil in grain alcohol and using this dilution to more precisely meter the amount of olive oil added.
Figure 1. Fermentation Temperature.
Figure 2. Wort Density vs. Time.
Figure 3. 4 hours fermentation - Oxygen (left) vs. Olive Oil (right).
Figure 4. 15 hours fermentation - Oxygen (left) vs. Olive Oil (right).
Figure 5. 20 hours fermentation - Oxygen (left) vs. Olive Oil (right).
Figure 6. 28 hours fermentation - Oxygen (left) vs. Olive Oil (right).
Figure 7. Time = Zero, Head Retention - Olive Oil (left) vs. Oxygen (right)
Figure 8. Time = 30 seconds, Head Retention - Olive Oil (left) vs. Oxygen (right)
Figure 9. Time = 60 seconds, Head Retention - Olive Oil (left) vs. Oxygen (right)
Figure 10. Time = 2 minutes, Head Retention - Olive Oil (left) vs. Oxygen (right)
Figure 11. Time = 3 minutes, Head Retention - Olive Oil (left) vs. Oxygen (right)
Figure 12. Time = 4 minutes, Head Retention - Olive Oil (left) vs. Oxygen (right)
1 Moonjai, N., (2003). Linoleic Acid Supplementation of Cropped Brewers Yeast: Uptake and Incorporation into Cellular Lipids and its Effect on Fermentation and Ester Synthesis. Dissertation, Katholieke Universiteit Leuven
2 Olive Oil Addition to Yeast as an Alternative to Wort Aeration, Grady Hull (New Belgium Brewing Co., Colorado), Masters Dissertation Thesis in Brewing and Distilling, 26 September 2005.