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Co-Products

The process of whisky distillation creates three distinct co-products; Draff, Pot Ale and Spent Lees.

Mash Tub

Draff

The spent grain from the mash tuns. Made up of hemicellulose, etc. is resistant to biochemical breakdown; the slow pace of reaction would require long retention times hence very large reactor volumes and capital cost. Moisture content is 70-80%; at large scale distilleries with potential for process integration, this may be dried to produce a solid biomass fuel with GCV around 21,000 kJ/kg however for small scale batch distilleries use as animal feed may be the preferred option.

Copper Stills

Pot Ale

This is the liquid residue from the wash still. The presence of yeast cells and dissolved barley solids gives this a high COD of around 65-71 g/l which is unsuitable for disposal untreated but useful for biogas production in an AD plant.

Spent Lees

This is the liquid residue from the spirit still. It has a lower COD concentration, typically around 3 g/l. It is expected that this may be mixed with the Pot Ale to give a liquid co-product with a COD of around 35 g/l which is suitable for biogas production in an AD plant.