Professor Johan Burger of Stellenbosch University has done research comparing old vines (55 years old) against young vines (7 years). I have been in email discussion with him about it.
Juice from berries of nine old and nine young vines were sampled at harvest time in January 2016 and showed significant differences in both sugar and titratable acid levels. RNA from the same plants, both berries and leaves, were extracted and sequenced. Significant differences in gene expression were noticed for genes which regulate ripening, sugar accumulation, cell wall degradation and the development of metabolites like anthocyanins.
The team also investigated the total viral and fungal populations in these plants. Old plants had higher numbers and more genetic variety among the viruses infecting them, whereas younger plants showed more diversity in the fungi associated with them.
The research results show that the gene expression in older vines are different from younger vines and suggest that the ripening process in the older plants takes longer, and may explain the development of flavour complexity, which often is associated with better quality wines.
I ascertained that the two groups were the same clone. Prof Burger told me
“In fact we were very lucky in that the young plants all originated from a single vine in the same vineyard. About ten years ago, one plant was selected, cuttings were made and grafted on exactly the same rootstock (Jacquez). These were subjected to virus elimination before being multiplied and interplanted in the same vineyard. In other words, in any given row, original (± 55-year old) plants and younger plants (7 yrs at the time of the experiment) grew under identical conditions.”
So he found that there are differences between old and young vines