The phenomenon has been thoroughly discussed. The fact that the frequency twin fruits increases when, during the blossoming period of the previous Summer, the maximum temperature exceeded 30°C. In addition, plants facing South produce more twin fruits than those facing North.
Rootstocks also influence the phenomenon, as has been noticed in those years when there were many twin fruits.
In conclusion, high temperatures during the differentiation period mean the phenomenon will appear the following year, just as happens for branches facing South. In addition, rootstocks interact with the seasonal trend - in particularly hot years, weak rootstocks generate twin fruits, leasing to higher costs related to post-harvesting selection.
