Dictionary.net

To renew, as wine, by mixing must with it and raising a new fermentation.

Unfermented grape-juice; must or new wine, often mixed with dead or vapid wine to raise a new fermentation; wine revived by being made by must to ferment anew. Hudibras.

To renew by mixing with must and fermenting anew. "We stum our wines to renew their spirits."-Sir J. Floyer: to fume a cask with brimstone.

n. [Dutch] Unfermented grape-juice or wine ; must.