I am curious about mead fermentations. I understand that the low nutrient content of mead musts necessitate nutrient addition(s) to insure vigorous and healthy fermentations.
I also understand that staged additions of these nutrients over several days can improve the performance of the yeast. In certain Lallemand strains, including one of my favorites, 71B-1122, the reference chart indicates that this strain has a low tolerance for O2 additions after the initial aeration.
Is it best practice in the case of low O2 tolerance to continue using a staged introduction of nutrients or to go with a single nutrient load at the front end?
I am also interesting in knowing what deficiencies in nutrient levels lead to fusel alcohol production in wine or mead fermentations. Can specific levels of given free amino acids be tied to production of the higher alcohols so seemingly common in mead fermentations?
Most honey is low in nutrients that yeast find necessary for a healthy cell and a vigorous and healthy fermentation. Yeast do respond better to staged additions over the first 1/3 of the fermentation.
All the nutrients added at the beginning will result in a high level of yeast cells with each cell having a low protein content. The fermentation will be vigorous in the beginning then fizzle out towards the end. Staged additions will result is a lower cell population with high protein.
This will produce a steady vigorous fermentation up to the very end. The high protein content in each cell will protect the cell from alcohol toxicity near the end of the fermentation. Staged or incremental additions of nutrients, namely nitrogen, will also minimize the production of H2S. A better way to interpret the reference chart regarding 02 and 71B-1122 is: the 71B strain requires less O2 for its growth phase than some of the others. Excessive O2 is not toxic to this strain. The introduction of O2 with staged additions of nutrients is no problem.
When there is an excess of amino acids the yeast catabolizes the amino acids via the Ehrlick pathway: deamination and decarboxylation to higher alcohol referred to as fusel oils. When there is a deficiency of amino acids, fusel oils are produced by the biosynthesis pathway from pools of alpha-keto intermediates.
Each amino acid is tied in with a specific higher alcohol. An over load of a specific amino acid should reflect itself in an increase of a specific higher alcohol.