I have gone back to the ideas of using olive oil and have been looking over many different research into different views on oxygen usage and the use of Oleic acid. Text from all the major scientists all spell out the need for good wort aeration, but in the two bottom recent ideas it was suggested that wort O2 need may be reduced or negated.
#1 I have read that it may be acceptable practice to simply introduce high DO into starters in order to create high levels of glycogen/sterols and thus reduces the need for wort aeration. Does anyone practice this or have any further info or “leads” to other discussions/research or white papers linking to this topic? I have found a few vauge discussions and some reference in text but wonder if somebody else has seen avenues I am missing.
#2 In some of the research using minute amounts of olive oil in the starter also created the high levels of sterols/glycogen and again negated the need for wort aeration and the yeast used will preform even better than if using wort aeration. Any first hand knowledge or other info sources on this?
It seems as though it was just a fleeting thought in the past by brewers of all levels but cant seem to find the final word on the two practices.
In the same way that dry yeast does not require oxygenation, you could “package” the yeast in a starter with all the reserves that they need to ferment, but figuring out how to do that will take some serious experimentation. I tried OO in starters for a while and found that it seems to work but it doesn’t improve the beer compared to O2, so why mess with it?
I’d say that varies with how much aeration happens during chilling and racking, as well as the strength of the wort.
I personally don’t buy the idea that a little monounsaturated fatty acid is going to completely replace all the biochemicals made using the O2 in the wort.
Shade, its interesting that you mention dry. Good point. I knew it was prepackaged with nessecary reserves and the reason all along that no starter was needed and actually detremental, but I just read some passages in Briggs just last night that refered to the fact that dry yeasts do not require molecular O2 in wort also due to these same manufacturing processes that never dawned on me.
Anybody know what the process is for dry yeast that makes them fortified? Are they just adding plenty of nutrient late and then drying the cells?
I haven’t heard that dry yeast don’t require oxygenated wort. You’d think that if they are going through a multiplication stage where they’re making cell membranes, that they’d need some O2 for production of sterols/unsaturated fatty acids.
“I always aerate my wort when using liquid yeast. Do I need to aerate the wort before pitching dry yeast?”
No, there is no need to aerate the wort but it does not harm the yeast either. During its aerobic production, dry yeast accumulates sufficient amounts of unsaturated fatty acids and sterols to produce enough biomass in the first stage of fermentation. The only reason to aerate the wort when using wet yeast is to provide the yeast with oxygen so that it can produce sterols and unsaturated fatty acids which are important parts of the cell membrane and therefore essential for biomass production.
Now that you post the Danstar FAQ. I know I have read that info along with their other yeast facts before, making it even more indicative of why this fact of dry yeast didn’t make itself clear enough to me in the past. Not the biggest fan of all the dry strains, but I have always recommended them for new brewers because of the high pitch count making starters a non-issue. That way they could concentrate on sanitation, temp and the other high priority needs to learn in the first batches.
Now that I understand the non-issue with wort O2 it brings. It just reinforces the reason to use it in practice just for ease and/or recommend it until a newer brewer is comfortable with process and will produce high quality beers in the short term and can then further branch out towards liquid strains and starters after batch 1-4 etc…
Here is the quotes I just fielded the other night about dry yeast from Brewing: Science and practice(Briggs, Boulton, Brooke and Stevens)( Woodhead publishing limited & CRC Press LLC: 2004: 881 pages) If you really want info overload this book is fantastic although awful pricey, currently used copies are listing across the net for $277-$371 and new copies are listing for $421. I was able to source this from an inter-library loan program that brought it to me from a major university. If you cannot find it in your local library system use worldcat.org to see if another city/ university close may have it etc…
Edit: complete passages showing why dry doesn’t require wort O2.
[color=#FF8000]"Such cells should be sterol replete and have little or no requirement for oxygenation of worts.
RE: Section 13.6 Fed-Batch aerobic cultures.
Theoretically it is an attractive proposition since not only are the biomass yields very high but derepressed yeast contains high concentrations of the essential membrane lipids, sterols and unsaturated fatty acids. These high lipid levels should reduce or eliminate the requirement for wort oxygenation.
In brewing fermentations the extent of sterol synthesis is modest compared to derepressed cells. Pitching yeast typically contains 0.1-0.2% of the dry weight as sterol.
This increases to approximately 1% of the cell dry weight at the end of aerobic phase of fermentation. The same yeast grown aerobically under derepressing conditions contains approximately 5% of the dry weight of sterol(Quain and tubb, 1982)."[/color]
Speaking to the drying process I also find some lines of text in the aforementioned book revealing the method.
“However, S. cerevisiae can withstand dehydration. Yeast used for baking and wine-making is routinely supplied in a dried form and this technique has now been extended to brewing yeasts(Fels et al.,1999). The dehydration process results in morphological changes. The cells take on a shrunken appearance and the plasma membranes develop deep invaginations(Rapoport et al.,1995). These changes are reversed during re-hydration. Survival rates are low and for sucessful drying the yeast must have been cultivated under aerobic fed-batch conditions. These cultural conditions are associated with elevated intracellular concentrations of trehalose and sterols, both of which probably protect membrane integrity during dehydration.”
Interesting, a happy coincidence that loading the cells with those compounds both protects them during drying and fortifies them during subsequent use.
This could explain some of the variability I’ve had from reusing yeast.
