stum

Concise Oxford English Dictionary © 2008 Oxford University Press:
stum /stʌm/

▶noun unfermented grape juice. ▶verb (stums, stumming, stummed)

• 1 prevent or stop the fermentation of (wine) by fumigating a cask with burning sulphur.

• 2 renew the fermentation of (wine) by adding stum.

– origin C17: from Du. stom (n.), stommen (v.), from stom ‘dumb’.