An initial alcohol fermentation by yeast. It is usually begun by adding an active yeast starter to a must or juice in a covered primary fermentation vessel. After a period of vigorous fermentation, the must is pressed or strained and/or the juice is transferred to a secondary fermentation vessel (e.g. a carboy or demijohn) and covered by an airlock. Even though the wine is now in a secondary fermentation vessel, the alcohol fermentation taking place is a continuation of the primary fermentation.
See also: Secondary fermentation.