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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.J. Robinson (ed) "The Oxford Companion to Wine" Third Edition pgs 77, 291, 322, 443 Oxford University Press 2006
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.
Following flowering, the flowers of the grape vine go through pollination and fertilization over the next 2 to 3 days. Here is another opportunity where incremental weather can influence the outcome with temperature drops below potentially damaging the ovules of the flowers before they can be fertilized. Since grapevines are hermaphroditic (containing both male and female parts) and usually rely on self-pollination, the presence of wind to circulate pollen or insects usually doesn't influence the success or failure of the pollination stage. While not as influential as temperature, the presence of rain can "wash off" the pollen from the stigma or greatly dilute the stigmatic fluid, causing the pollen to absorb too much water, swelling and bursting before it reaches the ovules.Winkler AJ, Cook JA, Kliere WM and Lider LA General Viticulture 2nd Edition, pgs 126–133 University of California Press 1974 .
Even in the most ideal conditions, usually only 20–30% of flowers develop into mature fruit with fully developed seeds and auxin production. If even fewer berries develop, the condition of coulure emerges while for developed berries, the number of seeds (or their absence) will influence the resulting size of the berries. Millerandge most often occurs when the partially fertilized grapes do not develop any seeds, leaving small (and potentially immature) berries present in a cluster of larger, otherwise mature berries.
However, the small, seedless berries may never fully ripen and stay hard and green (with high acid) throughout the growing season. Some growers may choose to remove clusters with high preponderance of millerandge through green harvesting or choose to harvest the entirety of the crop later at higher ripeness levels to balance the high acid and potentially "green flavors" of the shot berries. Other growers will remove the grape post-harvest at a sorting table along with other MOG.Clive Coates An Encyclopedia of the Wines and Domaines of France pgs 16 & 520 University of California Press; First Printing edition (June 2001)
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