You may find that as the bunches mature, the stems between the grapes actually lengthen and the bunch becomes looser. That's what happens on my vines. There are also grape varieties where the bunches are so tightly packed the grapes get flats on them where the grapes touch - some of the table grapes you buy in the shops are like this. So growers of those varieties don't see it as a problem, but rather a feature of that variety.

Short of individually pruning off individual grapes - something that might be done for grapes that are going to used for making certain very, very expensive wines, or planting a different grape variety, there is nothing practical you can do about it.

There are a great many varieties of grape. It is worth researching the properties of the variety before planting it. Nurseries sell a lot of totally unsuitable grape varieties to people. For example, I've seen things like Cabernet Sauvignon for sale in England, complete waste of space in our climate.