Millerandage (orshot berries,hens and chicks andpumpkins and peas) is a potentialviticultural hazard in whichgrape bunches contain berries that differ greatly in size and, most importantly, maturity. Its most common cause is cold, rainy or otherwise bad weather during theflowering stage of the vines though other factors, such asboron deficiency orfanleaf degeneration, may also play a role.[1]
While millerandage always causes a drop inyield, its impact on wine quality varies, particularly bygrape variety. For some varieties that are prone to unevenripeness within a cluster, such asSangiovese,Zinfandel andGewürztraminer, the development of millerandage may be unfavorable due to "green flavors" from the potentially unripe grapes hidden within the cluster. For other varieties, such asPinot noir or the Mendozaclone ofChardonnay, wine quality could be improved due to the reduced overall berry size and higher skin to juice ratio.[1]
The root cause of millerandage is the poor fertilization of grape flowers during thegrowing 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 hormoneauxin and facilitate the movement ofsugars in the vine) or viral infections can play a role.[1]
For grapevines, flowering occurs usually 8 weeks after the beginning ofbud break when the mean daily temperatures hit around 20 °C (68 °F). Usually flowering begins at the base of theinflorescence (cluster of flowers) and moves its way to the top. Following theapical dominance of grape vines, the uppermost shoots of the vine will begin flowering first with complete blooming taking place over 7 to 10 days. Ideally the temperature and weather condition for this period should be warm, sunny and dry to insure optimal flowering. For some varieties, such as Zinfandel andMerlot, flowering may be more staggered which poses a greater risk for inclement weather disrupting the process and encouraging millerandage. Some growers may try to encourage more synchronized flowering with the use of chemical treatments, such ascyanamide.[2]
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 10 °C (50 °F) potentially damaging theovules of the flowers before they can be fertilized. Since grapevines arehermaphroditic (containing both male and female parts) and usually rely onself-pollination, the presence of wind to circulate pollen or insects usually doesn't influence the success or failure of the pollination stage.[2] While not as influential as temperature, the presence of rain can "wash off" the pollen from thestigma or greatly dilute the stigmatic fluid, causing the pollen to absorb too much water, swelling and bursting before it reaches the ovules.[3]
Even in the most ideal conditions, usually only 20–30% of flowers develop into mature fruit with fully developed seeds and auxin production.[2] If even fewer berries develop, the condition ofcoulure 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.[1]
While millerandage will always have an economic impact in reducedharvest yields, it may not always have a negative impact on the resulting quality of the wine. In some areas, such as theNew World wine regions ofAustralia,California andNew Zealand, the presence of millerandage in the a vineyard can be seen as a positive quality for avintage due to the reduced average berry-size.[1] Some growers will even use chemical sprays to deliberately encourage millerandage.[4]
However, the small, seedless berries may never fully ripen and stay hard and green (with highacid) throughout the growing season. Some growers may choose to remove clusters with high preponderance of millerandge throughgreen 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 otherMOG.[5]
