Coulure is a grapevine condition in which flowers or newly formed berries fail to develop and drop from the bunch after flowering. It results in poor fruit set and a reduced crop. The French term is used in viticulture to describe a loss of potential berries rather than a disease caused by one specific pathogen.
Cold, wet, windy or otherwise unfavourable weather during flowering can interfere with pollination and fertilisation. Vigorous vine growth, nutritional imbalances and variety-specific sensitivity can also contribute. Merlot and Grenache are often cited as varieties that may be susceptible, although the degree varies by site and season.
Coulure can leave bunches loose and sparse, reducing yield and making production less predictable. The remaining berries may ripen normally, but the overall crop volume is lower. The economic impact depends on the severity of the event, the vineyard’s expected yield and the value of the grapes.
Example: a cold, rainy period during flowering in Bordeaux may contribute to coulure in Merlot, leaving fewer berries per bunch and reducing the harvest.
Coulure is the dropping or failure of flowers and young berries. Millerandage is uneven berry development within the bunch, often leaving a mixture of normal and very small berries. Both can occur in the same vintage and are associated with flowering and fruit-set conditions.
Chef’s note: coulure is a viticultural issue that affects grape yield. It should not be confused with berry rot or a wine fault.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
