Flowering has started in early ripening varieties like Chardonnay, Pinot Noir and it’s cousin Pinot Gris. Sauvignon Blanc will have started by the end of the first week of December in early ripening areas.
The individual flowers on the grape bunch structure (rachis) are covered by a ‘calyptra’ (also commonly known as a cap) and during hot fine weather the cap, which resembles a granny bonnet, splits open and pops off revealing the yellow flower parts. Grape flowers are wind pollinated so if it is hot, dry and windy then the whole flowering/capfall process can take as little as 3 days from start to finish. However, if it rains during this period the caps stick to the flower and fail to pop off, so the flower is not exposed to the wind, and no pollination takes place thus no grape develops. Also, if it is cold during this period even if the cap is removed the pollen tube may fail to develop resulting in the flower aborting. In these conditions capfall can last up to 14 days. So at this time of year we always hope for hot, dry and windy weather.
Capfall is an important time for spraying grapes against fungal diseases that will afflict them later in the season during ripening. It is a critical time in the grape growing calendar.
Following capfall the next phase is called fruitset where we see tiny grapes form where the flowers were. At this stage we can tell whether it will be a bumper crop or not by how many berries/flowers abort and how many set fruit. Berries can form but later shed from the bunch if a cold spell strikes. This is called ‘shatter’. The French refer to this phenomenon as ‘collure’ or ‘hen and chickens’ – which is when there are small undeveloped berries – chickens, as well as fully developed berries – hens.
(The photograph shows the Dambuster Pinot Noir at the Woolshed vineyard)