Jeff’s Corner 5-20-22

Howdy, everyone!

Today we will talk about “fruit set,” which is the third installment in our five-part series on the life cycle of a grapevine. You can check out the first two parts, bud break and flowering, in earlier blogs.

There are two main stages in the maturation of a grape cluster, the growth phase and the ripening phase. Fruit set begins the growth phase. The pollinated flowers become grapes quickly, and are about the size of a BB. There are gaps between them on the cluster that fill in as the grapes grow larger in size.

During the growth phase, all grapes (red or white) are green in color and hard in texture. They don’t turn color and become pliant until the beginning of the ripening phase, which will begin around mid-June. During the growth phase, the juice in the grapes is extremely acidic, and sugars won’t begin to develop until they stop growing and begin to ripen.

Fruit set can be measured quantitatively as the percentage of flowers that turn into grapes. Average fruit set is typically between 30 to 50 percent. Normal fruit set, however, varies from one grape variety to another. For example, normal fruit set for Cabernet Sauvignon can be as low as 20%. The success of fruit set can be more easily measured by how complete (compact) the clusters are when the grapes reach full size.

Whereas late freezes, high winds, and hail were our primary threat to a successful harvest during bud break and flowering, now we are concerned with larvae and disease. Caterpillars are voracious, and powdery and downy mildew can spread through a vineyard quickly. In moist, warm climates like ours, fungal diseases like black rot are also a concern.

We’ll continue with this series in a month or so when we talk about veraison (color change,) which begins the ripening phase of a grape cluster. In the meantime, there are lots of new vintages being released, so be sure to watch for stories and tasting notes on all these in upcoming installments of Jeff’s Corner.

See ya soon…