Yeast hulls
yeast ghosts, inactivated yeast cell walls
Detoxify a stuck ferment and give the yeast a surface to work from.
Typical dose
Around 0.2 to 0.5 g/L when restarting a stuck wine.
When to add it
When restarting a stuck fermentation, alongside a fresh starter.
In practice
The cell walls adsorb the toxic medium-chain fatty acids that build up in a struggling ferment and inhibit the yeast further, and they also provide nucleation sites and trace nutrients. They are part of a restart protocol rather than a routine addition, and they will adsorb a little copper on the way.
Linked faults are the ones this addition either treats or, used wrongly, causes. The fault page says which, and whether it can be undone.
Others in nutrients and enzymes
Diammonium phosphate
Inorganic nitrogen for the yeast, the direct fix for a starved ferment.
Complex yeast nutrient
Nitrogen plus the amino acids, vitamins and sterols the yeast also needs.
Rehydration nutrient
Primes dry yeast with micronutrients before it is pitched.
Thiamine
A micronutrient that helps a ferment finish and lowers SO2 binding.
Pectic enzyme
Breaks down pectin to clear haze and free juice and colour.
Glucanase
Breaks down Botrytis glucans and speeds lees ageing and filtration.
Beta-glucosidase
Frees the bound aroma compounds locked up in aromatic white grapes.