Coulure and Millerandage

Coulure is the abnormal shedding of flowers and tiny fruitlets during or immediately after flowering, resulting from failed pollination or fertilization. The primary cause is adverse weather during the critical 10 to 14 day bloom period: temperatures below 15 degrees Celsius, persistent rain that washes pollen from stigmas, and strong winds that disrupt the delicate pollination process. Nutritional imbalances, particularly boron deficiency, can also contribute. In severe cases, entire flower clusters may fail to set any fruit, while moderate coulure results in loose, gappy bunches with fewer berries than normal. Unlike millerandage, coulure represents a complete loss of potential berries, and there is no way to recover the yield in the affected vintage. The condition is especially damaging in regions where flowering occurs during unpredictable spring weather.

• Caused by cold (below 15C), rain, or wind during the 10 to 14 day flowering period that disrupts pollen transfer and fertilization
• Boron deficiency in vineyard soils can exacerbate coulure by impairing pollen tube growth, even in otherwise favorable weather
• Results in loose, gappy bunches with fewer berries; severe cases can eliminate entire clusters
• Yield losses are permanent and unrecoverable within the affected vintage

Millerandage occurs when pollination is partially successful, producing bunches that contain a mix of normal-sized seeded berries and abnormally small, seedless berries known as shot berries or millerands. The French term 'millerandage' derives from the visual resemblance to a mother hen surrounded by her chicks, which gives the condition its English nickname 'hens and chicks.' The shot berries develop from flowers that were pollinated but not fully fertilized, so the ovary swells slightly but never produces seeds or reaches normal size. These tiny berries have a much higher skin-to-juice ratio than normal berries, concentrating sugars, acids, and phenolic compounds. The causes overlap significantly with coulure: cold or wet weather during bloom, nutritional stress, and varietal susceptibility.

• Shot berries (millerands) result from incomplete fertilization: pollination occurs but seeds fail to develop, producing tiny seedless berries
• The high skin-to-juice ratio of shot berries concentrates sugar, acid, anthocyanins, and tannins in the resulting juice
• Named 'hens and chicks' in English for the visual contrast between large normal berries and small shot berries in the same bunch
• Harvest timing becomes more challenging because normal and shot berries ripen at different rates within the same cluster

Certain grape varieties are genetically more prone to coulure and millerandage due to their flower structure and pollination biology. Merlot is notoriously susceptible, and severe coulure events in Bordeaux have historically caused significant Right Bank yield losses. Grenache, with its upright flower clusters exposed to wind, is another high-risk variety, and coulure is a perennial concern in Chateauneuf-du-Pape and other Southern Rhone appellations. Malbec is vulnerable in both its native Cahors and in Argentine vineyards at high altitude where spring weather is unpredictable. Muscat varieties, with their complex floral biology, frequently experience millerandage. Conversely, varieties like Cabernet Sauvignon, Syrah, and Chardonnay are generally more resistant due to their flower structure and self-pollinating characteristics.

• Merlot: highly susceptible to coulure; the 2017 Bordeaux vintage saw 30 to 40 percent yield losses on the Right Bank
• Grenache: upright flower clusters and wind exposure make it vulnerable in Southern Rhone and Spanish Garnacha plantings
• Malbec: susceptible in both Cahors and high-altitude Argentine vineyards where cold spring snaps disrupt bloom
• Cabernet Sauvignon and Syrah: generally more resistant due to self-pollinating flower structure and favorable bloom timing

Preventing coulure and millerandage focuses on optimizing vine health and managing canopy conditions during the critical bloom period. Balanced vine nutrition, particularly adequate boron and zinc levels in the soil, supports healthy pollen development and tube growth. Canopy management that improves air circulation and light penetration around flower clusters helps moderate the microclimate during bloom. Some growers use foliar boron sprays in the weeks before flowering as a preventive measure. Clone selection also plays a role: nurseries have developed clones of susceptible varieties like Merlot and Grenache that show improved fruit set under marginal conditions. However, weather remains the dominant factor, and no viticultural technique can fully prevent these conditions during an exceptionally cold or wet flowering period.

• Soil and foliar boron applications before flowering support pollen development and reduce coulure risk
• Canopy management to improve air circulation and warmth around flower clusters helps moderate bloom-period microclimate
• Clone selection: newer clones of Merlot and Grenache bred for improved fruit set under marginal flowering conditions
• Weather remains the dominant factor; no management practice eliminates risk during severe cold or rain events at bloom

While coulure is universally negative for growers because it simply eliminates potential crop, millerandage occupies a more nuanced position. Quality-focused producers, particularly in Burgundy and the Northern Rhone, sometimes view moderate millerandage as beneficial. The concentrated juice from shot berries, with its elevated sugar, acid, and phenolic levels, can add intensity and complexity to the final blend. In Burgundy, some vignerons note that vintages with mild millerandage produce wines of greater depth and aging potential, essentially achieving a natural form of yield reduction. The trade-off is economic: lower yields mean less wine to sell, and the uneven ripening of mixed-size berries complicates harvest timing. For this reason, the quality benefit is most appreciated by small estates producing premium wines where per-bottle value outweighs per-hectare volume.

• Moderate millerandage is viewed positively by some Burgundy and Northern Rhone producers for the concentration it brings
• Shot berries contribute juice with elevated sugar, acid, anthocyanins, and tannins, acting as a natural yield reducer
• Uneven ripening within clusters complicates harvest timing: normal berries may be ready while shot berries are still underripe or overripe
• The quality benefit only has economic value for premium estates where per-bottle price compensates for reduced yields