Crop Thinning - Q&A

I've enjoyed reading your thoughts and comments on various viticulture issues. I have a question (actually, quite a few), the first relates to crop thinning and the most appropriate time to do so to enhance quality. I've read various articles that suggest doing so at veraison gives you the opportunity to eliminate bunches that are a bit tardy to set, whilst others suggest that it must be done well in advance of veraison. Any ideas on this?
Hi Grant,

At the risk of sounding heavy handed- crop thinning is not really a very good habit to get into. It is expensive and is best avoided by trying to 'balance' a vineyard so it is not necessary.

It does have some uses in young vineyards that are overcropped (pictured upper left), or varieties that have a large variation in their flowering and ripening (Grenache ; Zinfandel).

In these cases taking off any green fruit at verasion helps reduce the amount of unripe, or less than ripe fruit that goes into making wine. With Zinfandel they can leave unripe fruit and hand pick it later as a second crop. As a rough rule of thumb the earlier unripe crop is removed the better it is for wine quality, as the energy produced from the vines leaves goes to remaining crop longer, therefore the fruit has 'ripening power' to produce flavour colour etc.

The trouble is how do you explain the concept of removing just the right crop to someone who hasn't spent a lot of time in a vineyard and doesn't understand the concept of vine balance. We use simple rules of thumb to make it easier to accomplish. At verasion you instruct 'If it is green cut it off, if it is red leave it there.'

The obvious point here is at verasion if the fruit hasn't coloured up if will be less ripe compared to bunch that has fully coloured up. Another way of giving instruction is to cut off fruit from shoots that are less than 30cm long. Short shoots with fruit on them is a sign the vineyard vigour and crop load are not balanced. Experienced labour can also remove clumps of fruit (lower left).

Pruning is the time to do your 'crop thinning' by getting the bud number right for your vines vigour. The vineyard should produce 5 kg of Fruit of 1 kg of Canes. 5:1. The Fruit weight/cane weight is called the Ravaz index. You should leave 30 buds per kg of canes removed. Much better explanation in 'Sunlight into Wine' for more info.

I know it is from the text book but it simple but very effective, especially after a few years of balance.

Regards James