Millerandage

Millerandage (or shot berries, hens and chicks and pumpkins and peas) is a potential viticultural hazard in which grape bunches contain berries that differ greatly in size and, most importantly, maturity. Its most common cause is cold, rainy or otherwise bad weather during the flowering stage of the vines though other factors, such as boron deficiency or fanleaf degeneration, may also play a role.

While millerandage always causes a drop in yield, its impact on wine quality varies, particularly by grape variety. For some varieties that are prone to uneven ripeness within a cluster, such as Sangiovese, Zinfandel and Gewürztraminer, the development of millerandage may be unfavorable due to "green flavors" from the potentially unripe grapes hidden within the cluster. For other varieties, such as Pinot noir or the Mendoza clone of Chardonnay, wine quality could be improved due to the reduced overall berry size and higher skin to juice ratio.

Causes

The root cause of millerandage is the poor fertilization of grape flowers during the growing season. While this is most often attributed to bad weather, other factors such as nutritional deficiencies (particularly of the mineral boron which is needed to synthesis the growth hormone auxin and facilitate the movement of sugars in the vine) or viral infections can play a role.

Flowering and fruit set

For grapevines, flowering occurs usually 8 weeks after the beginning of bud break when the mean daily temperatures hit around 20 °C (68 °F). Usually flowering begins at the base of the inflorescence (cluster of flowers) and moves its way to the top. Following the apical dominance of grape vines, the uppermost shoots of the vine will begin flowering first with complete blooming taking place over 7 to 10 days.