Nitrogen assimilation: uptake by the yeast

The standard

The assimilable nitrogen amount measures how much nitrogen the yeast can actually take up — determined as the sum of ammonium and free amino acids, not as total nitrogen. Its course over the fermentation matters, not only its starting value.

Criteria

• What is measured is ammonium plus usable amino acids, not total nitrogen
• Below a threshold the fermentation stalls
• An excess favours off-flavours
• The timing of uptake counts, not only the total amount

Distinction

Nitrogen assimilation ≠ nitrogen supply: assimilation is the uptake by the yeast, supply the availability in the must. An assimilable nitrogen amount remains a statement about what can be taken up, not about what is present.