This vine disease is indirectly caused by the vinegar fly, which covers grapes with its eggs and thereby infects them with acetic acid bacteria (see under Acetobacter). This occurs on berries that have already been damaged by various circumstances, whether by mechanical injury (for example, damaging birds) or by various moulds that have already attacked the berries. In the latter case, this means that vinegar rot occurs in combination with various types of grape rot. The berries contain numerous larvae (maggots) that move around briskly. Ripening berries turn greenish to reddish in white wine varieties and brown to purple in red wine varieties. These contain less sugar, but too much acetic acid and gluconic acid. In the advanced stage, a penetrating smell of vinegar is perceptible. In the final stage, the berries are empty and have a mummified skin. Such grapes must be discarded as they can cause the wine defect acetic souring in the wine. See also all pests and diseases under vine enemies.
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Technischer Lehrer, staatl. geprüfter Sommelier, Hotelfachschule Heidelberg