Zinc is an essential trace element required for yeast growth and therefore insufficient zinc will lead to slow or sticking fermentations.
There is no general correlation between the zinc content of the malt and that of wort because of variable losses in spent grains and trub.
Range of Values
It appears that the normal range is 0·05 – 0·1 mg per litre but up to 0·25 mg per litre may be necessary. The amount needed depends on yeast strain used, process conditions and the concentration of chelators. Too high a level can, in some cases, lead to yeast autolysis and, therefore, produce sulphury off-flavours.
Normally sufficient zinc is extracted during wort production but where deficiencies occur, or as a precaution, zinc can be added as a constituent of yeast food or as zinc sulphate or chloride. It is therefore desirable to check the zinc content of the wort at regular intervals and particularly in cases of fermentation difficulties.
The concentration of zinc is measured using an Atomic Absorption spectrophotometer.