Originally Published by Tracy Aquilla in Brewing Techniques (Volume 5, Number 2)
"Through it flies in the face of popular wisdom, yeast does not go through a respiration phase in the early stages of fermentation. A careful look at yeast metabolism and reproduction reveals a common misunderstanding and points the way to more sophisticated applications of oxygen in the brewery.
Fermentation is perhaps the most interesting and exciting part of brewing beer. There is something fascinating about watching yeast in action, and being close to the process contributes immensely to my enjoyment of my beer. No matter how well we do our part in preparing bitter wort for fermentation, it is the yeast that turns it into beer. For this reason alone, it is important to understand and appreciate what these microorganisms are really doing inside our fermentors. Most of the popular brewing literature, however, fosters a misconception about yeast and fermentation. This articles sets the record straight.
Most of the brewing literature indicates that brewers’ yeast (Saccharomyces cerevisiae and S. uvarum) required dissolved oxygen for a brief period of time after pitching so the cells can respire and grow, implying that yeast needs oxygen to bud and must respire before it can ferment wort. It is true that aerating or oxygenating wort is generally beneficial to fermentation, but it is untrue to say that yeast requires oxygen to reproduce or that yeast uses oxygen to respire during fermentation. The misunderstanding may be subtle, but it is a misunderstanding nonetheless. Gaining a clear understanding of the truth about how yeast works not only sets us on sound technical foundations, but has practical applications as well. This article briefly discusses yeast metabolism, clarifies the role of oxygen, and suggests some practical applications of this more refined understanding of fermentation processes."
There was a very interesting research thesis published by Grady Hull entitled "Olive Oil Addition to Yeast as an Alternative to Wort Aeration" which can be found here.
In short, Grady sought to find an alternative to aerating wort. It would theoretically have the advantage of reducing the exposure to oxygen and therefore downstream events from the oxidation of compounds produced during fermentation.
"The real requirement for oxygen, then, is to help produce fatty acids and sterols, which are very important components of the cell membrane. The reason wort aeration (or oxygenation with pure oxygen) is considered so important to brewery fermentations is that yeast can synthesize the lipids needed for membrane biosynthesis only when dissolved oxygen is available. If yeast had an independent source of these important lipids, however, the so-called requirement for oxygen could theoretically be eliminated completely." - MoreBeer
"By mixing olive oil into the yeast, during storage, instead of aerating the wort, fermentations can be achieved with only minor increase in fermentation time. The beers produced from these fermentations were comparable in flavor and foam retention to beers produced by traditional wort aeration. The ester profile of the beers produced using olive oil addition was significantly higher than the controls and the flavor stability of these beers was significantly improved." - Grady Hull, Abstract
Role of Ergosterol in Yeast: "Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol found in cell membranes of fungi and protozoa, serving many of the same functions that cholesterol serves in animal cells. Because many fungi and protozoa cannot survive without ergosterol, the enzymes that create it have become important targets for drug discovery. Ergosterol is a provitamin form of vitamin D2; exposure to ultraviolet (UV) light causes a chemical reaction that produces vitamin D2." -Wikipedia
Experiment results:
"Overall, the experimental beers and the controls were very similar — similar enough that the brewery released the final experimental batches to the public. Head retention times in the experimental beers were only slightly less than that seen in controls. Fermentation times were slightly longer, but the differences between the experimental and control groups shrunk as the amount of olive oil increased. And, the beers made with olive oil attenuated as well as the control beers. Ester production was greater in the experimental beers (and remember that ester production increases as wort aeration decreases), but not to the degree that the tasting panel thought it was outside of the brand’s specifications. In fact, the tasting panel preferred the olive oil beers to the controls. And finally, when the tasting panel compared beer samples that had been aged warm for three weeks, they detected less oxidation in the olive oil beers than the aerated beers. In short, Hull’s four experiments supported the idea that olive oil could be used as a replacement for aeration, increasing the flavor stability of a beer — at least in the case of average strength ales." - BYO Olive Oil Summary
White Labs also conducted some experiments found here.
More White Labs data here.
How Much Olive Oil Should I Use?
"So how much olive oil in beer yeast should I be using? During the trials, New Belgium brewery would pitch 4500 liters of yeast into 168000 liters of beer. Into the 4500 liters of yeast, they would add 300 ml of oil. To scale this down for 5 gallons, we need to use about 0.0000833 ml of oil. For almost everyone, this is impossible to measure. There are 60 drops of olive oil in a teaspoon, and a teaspoon is 5 ml, so a drop is about 0.0833 ml. You would need about 0.001 or 1/1000 of a drop. As you can see, the amounts are miniscule. It was suggested on Northern Brewer's forum that one way to get this small amount would be to dip a toothpick into the olive oil and then transfer this amount over to the wort."
Source: Winning-HomeBrew.com
"Olive oil will not dissolve in wort and must first be dissolved in 100% ethanol. For any homebrewers reading this – do not add a drop of olive oil to your beer. I had to weigh 1 gram of oil, dissolve it, and make a serial dilution until I had close to 0.1 ug/ml."
Source: ScienceBrewer.com
Ever wondered if a square keg would work? This clever patent shows that it can be done. No indication how much pressure it could safely handle. It would need to stay less than 5 ATM with a good pressure release valve and be safely tested first.
You can take a closer look at the following link to *US4093099. 1 cubic foot holds 7.48 gallons or 28.3 liters. 4 cubic decimeters or about 12 inches equals 4 Liters.
