Thompson Seedless Grapes

Grapes, however, are the very picture of fragility: nothing more than thin-skinned little bags of juice.

In her book, How to Pick A Peach, Russ Parsons described "table grapes are essentially nothing but guilt-free snack foods – conveniently packaged sugar water that allows you to feel virtuous while you eat it."

The dominant table grapes today are varieties such as Thompson Seedless, Ruby Seedless, Crimson Seedless and Flame Seedless. Their primary selling point is self-explanatory: seedless. It’s hard to be a popular convenience food when people have to interrupt their snacking to spit out the pips.

photo: Vineyard @ Rhine Valley, Germany (2009)
Originally called the Sultanina Bianca, Thompson Seedless was popularized in the US by William Thompson, a Californian nurseryman in the late 19th century. Today the Thompson seedless grape is the most popular table grape as well as one of the most versatile. It is also used for juice and inexpensive wine and accounts for 95 percent of the raisins produced in California.

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Properly grown and matured to full ripeness, the Thompson Seedless has startlingly good flavor – a pleasingly flowery quality. The problem is that you can rarely find a fully mature Thompson Seedless in the market. When ripe, the variety has a tendency to ‘shatter’ – that is the grapes fall off the bunch. This is inconvenient for the growers, the retailer and the consumer. And so Thompson Seedless are usually picked when they are still green. At this point they can be sweet, but they are never much more.

The Thompson Seedless is coddled like some kind of exotic bonsai tree. Not only are the vines trained to grow along specially designed trellises, but they are also meticulously pruned to manage the right number of leaves, the right number of shoots and the right number of grape clusters. And that is just the start.

photo: Vineyard in Melbourne (2005)

Left on its own devices, the Thompson Seedless vines produces grapes that are quite small, particularly when picked early. To get around that, farmers have come up with some innovative techniques to increase grape size. Between girding and gibbing, a farmer can increase the size of an individual grape by as much as a third.

Girdling – which involves cutting a ring in the bark all the way around the base of the vine just as the grapes begin to emerge (and often again as the grapes begin to gain color). This interrupts the flow of nutrients to the leaves and concentrates them in the fruit.

Gibbing – applying gibberellic acid, a naturally occurring plant growth regular extracted from a cultivated fungus. It increases the size of individual grapes and also stretches out grape clusters, allowing better air circulation and thus reducing disease.

source: How to Pick a Peach