I've talked about fruit thinning before, and here's another missive.
Common in commercial practice is to do thinning at colour change, so that you can remove the fruit that is less-advanced in ripening - i.e. the stuff that hasn't gone through veraison as soon as the bulk of it.
When you do this, you're advancing the maturty of the harvested fruit. However, this is only so because you have removed that tail end of the fruit -all the stuff that's less ripe, so that the average brix is higher, and that carries on through to harvest.
But, what if you remove fruit randomly at that point in the season? I don't believe you will see much of an effect on Brix at harvest, if at all.
I think this is because regardless of how much fruit is on the vine (within reason!), the rate at which it will accumulate brix won't change much. The conduit for the sugars to pass through is the phloem, and under the conditions in the vine during ripening, sugars are already moving through and into the berry as fast as they can. Removing fruit might mean the vine has more carbohydrates available, but that doesn't mean that the pipes (phloem) leading to the berries can push more sugar into the berry. There is a limit!
In fact, there is evidence that the size of fruit is related to the diameter of the stem that leads to that fruit (i.e. a larger number of pipes leads to a larger fruit), such as this paper working with citrus. This doesn't necessarily mean cause and effect, but it is a logical conclusion.
It might also mean that if you think the fruit early enough (within a couple of weeks post-fruit set), you might be able to enhance the ripening of the fruit because the pedicels can grow larger due to the greater amount of carbohydrate available? I wish I knew the answer to that question!!
When you do this, you're advancing the maturty of the harvested fruit. However, this is only so because you have removed that tail end of the fruit -all the stuff that's less ripe, so that the average brix is higher, and that carries on through to harvest.
But, what if you remove fruit randomly at that point in the season? I don't believe you will see much of an effect on Brix at harvest, if at all.
I think this is because regardless of how much fruit is on the vine (within reason!), the rate at which it will accumulate brix won't change much. The conduit for the sugars to pass through is the phloem, and under the conditions in the vine during ripening, sugars are already moving through and into the berry as fast as they can. Removing fruit might mean the vine has more carbohydrates available, but that doesn't mean that the pipes (phloem) leading to the berries can push more sugar into the berry. There is a limit!
In fact, there is evidence that the size of fruit is related to the diameter of the stem that leads to that fruit (i.e. a larger number of pipes leads to a larger fruit), such as this paper working with citrus. This doesn't necessarily mean cause and effect, but it is a logical conclusion.
It might also mean that if you think the fruit early enough (within a couple of weeks post-fruit set), you might be able to enhance the ripening of the fruit because the pedicels can grow larger due to the greater amount of carbohydrate available? I wish I knew the answer to that question!!
