Maximum Yeast Performance

The performance of living yeast cells can be affected in many ways. Shipping and distribution can expose the yeast to temperatures which are harmful. Most of our products are shipped air freight, midweek to minimize transit time. Even with that we find some detrimental exposure on occasion. Loss of viable cells by age or temperature exposure are the most common beginnings of problems. If this is compounded by other factors, the performance can become unsatisfactory. A number of these are listed below.

Preparing a starter Culture Solution...

To make more mash, or increase the pitching rate, if the package is aged or not used right after it swells, boil a pint of wort S.G. 1.020 - 30 using 3 -4 tablespoons malt extract in 2 cups of water for 15 minutes. Cool to 75 F., add yeast and incubate for 12 hours or until high krausen.

Using the optimum timing and temperatures...

Delaying the use of the yeast after it starts incubating, whether from the package or a starter, can reduce performance. Make transfers in approximately 24 hr intervals at 75° F. Maintain at 75° F during incubation. Colder or warmer by a few degrees is significant. Longer or shorter time periods are significant.

High gravity worts...

(1.056 and greater need more yeast). Double the yeast amount for every 0.008 S.G. above 1.048.

Nutritients

Yeast produces 33 times more alcohol while reproducing than when resting. Once the nutrients have run out, and the fermentation has become "stuck" or sluggish, it is then too late to provide either nutrients or new yeash. If this happens really early during the fermentation, then you're in trouble.This is because when a yeast is deprived of a nutrient, it grows as best as it can with what is available, and then growth comes to a halt. Those cells are then put together with less than satisfactory levels of (lets say) protein due to deficient nitrogen. Their enzyme content is less than adequate, and they don't metabolize well at all. Growing cells are ~33 x faster at ethanol production than non-growing cells. Supplementation at that point does not reinitiate growth in the older cells. By that time the medium is higher in alcohol and still deficient in some nutrients. Some cells may even have died. Even supplying the combination of BOTH nutrients and new yeast won't get the activity restarted again. So the trick is to ensure you have enough nutrients available at the start of the fermentation.

The most common limiting factor for yeast growth is a lack of nitrogen. Nitrogen is approx 9% of the cell mass. Most common form to add it is as the ammonium ion, as the sulphate and phosphate salts (phosphorus is approx 1-2% of the cell mass, and sulfur 0.3-0.5% so these are needed too - this is a nice way of getting all three in there). Add the ammonium phosphate at a rate of 25-50 gr for a 25L wash.

In the old days - the advise was to add dried raisins and canned tomato paste concentrate to the wash. Usually this did not help much and even could result in an infected wash which would end up in the sink.
Nowadays, more advanced yeast nutrients are commercially available, also for the small scale homedistiller.

Some examples are:
-

Acidity
A slightly acidic environment is enjoyed by yeast, and also inhibits the development of bacterial contaminants. The pH of the brew should be adjusted to between 4.0 and 4.5 prior to fermentation, using citric or lactic acids. You can also use lemon juice rather than citric acid for distilling. Just use it on an equal volume basis- 1TBSP of acid blend = 1TBSP of lemon juice.

Aeration...

is extremely important for all worts. The second most common limiting factor in the fermentation process is a lack of oxygen, but it only needs it during the first day until high cell numbers are present. Make sure that you have aerated the wash well just prior to adding the yeast. "Splash filling" is enough to do the job. Do not do this too much later during the fermenation.

Dissolved oxygen ...

is required for the respiration of yeast at the onset of fermentation. One good method of providing dissolved oxygen for yeast is when preparing a starter solution, use a jar or flask with adequate headspace, then agitate the container frequently while fermenting. By doing this, you will provide more dissolved oxygen to the yeast when it is most needed.

Uniform Temperatures are important...

keep at 75° F until fermentation is evident, and then adjust to the desired temperature. Fluctuations from night to day need to be minimized.

Wort Composition...

effects the amount of head thrown, and can vary among different yeast strains. Some ale and lager strains produce little or no head at first in some worts, although fermentation may be active, it may not be readily evident.

Barley malt is nearly a complete nutrient source for yeast growth. The addition of some nitrogen, vitamins, and trace elements is beneficial, but your yeast will survive without it!

 

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