What is Phenolic ripeness? And is climate change effecting grapes ripening?

There are certain words that pop up in my day to day work and I always assume that I know what they mean. Sometimes these words are rather specific to the wine world. One such expression is 'phenolic ripeness'.
A phenol is an aromatic organic compound with the molecular formula C₆H₅OH.
According to the Drugbank website:
 'Phenol is an antiseptic and disinfectant. It is active against a wide range of micro-organisms including some fungi and viruses, but is only slowly effective against spores. Phenol has been used to disinfect skin and to relieve itching. Phenol is also used as an oral analgesic or anesthetic in products such as Chloraseptic to treat pharyngitis. Additionally, phenol and its related compounds are used in surgical ingrown toenail treatment, a process termed phenolization. Research indicates that parental exposure to phenol and its related compounds are positively associated with spontaneous abortion. During the second world war, phenol injections were used as a means of execution by the Nazis. Phenol is a toxic compound whose vapours are corrosive to the skin, eyes, and respiratory tract.'




 Clearly the amount of phenol in grapes is quite small and not poisonous, but it is an important molecule that has to be assessed.

These look ripe, but are they????

Justin Howard-Sneyd MW explains phenolic ripeness in Decanter magazine:

 'As grapes ripen, sugar levels increase, and acidity levels decrease. Fruits in the wild spread their genes by persuading animals or birds to eat their fruit; they then excrete the seeds, hopefully in a favourable spot. The fruit must taste delicious, so flavour molecules build up as the grape approaches ripeness.

Winemakers often use potential alcohol as a guide to when the grapes should be picked. But the ideal level of potential alcohol for a particular wine, say 13%, does not always correspond to either the flavour ripeness (when the grapes taste great) or phenolic ripeness. Phenols are complex molecules, including tannins, in the skins of the grape that can contribute bitter flavours. As the grape approaches ripeness, they change from green and bitter to pleasantly astringent, to soft and ripe-tasting.
If noticeably bitter flavours dominate the palate, then the wine is not considered to have achieved phenolic ripeness. If, however, the tannins of a red wine are supple and rounded, then the grapes used were phenolically ripe when picked.'

 According to 'An analysis of seed colour during ripening of cabernet sauvignon grapes' in the South African Journal of Enology and Viticulture
' Achieving phenolic maturity is a strong reason to delay the harvest, even after technological maturity occurs; in addition, climate change accentuates the delay between technological maturity and phenolic maturity (Meléndez et al., 2013). Bindon et al. (2013) highlighted that consumers preferred Cabernet Sauvignon wines from grapes harvested later.' 

Another description of phenolic ripeness , which makes sense is 'physiological ripeness'.

My sons helping with the grape harvest a few years ago in the Languedoc. They were keen to taste and assess the ripeness.

For me phenolic ripeness is the precise moment when all the important elements of acidity, sweet ripeness and tannins are in perfect balance. Grapes can be tested in laboratories for sugar levels and potential alcohols, but often a human assessment is required to assess this phenolic ripeness. When I walk through the vineyards every year in Bordeaux and the Languedoc at the end of the Summer, the grapes are looking lush and full, but they are changing all the time. The energy of the vine is transmitted from the leaves and foliage onto the development and ripening of the bunches of grapes.
When I taste the grapes, I look for the colour of the pips and the intensity of the grape skins. The pips are a crucial element for determining the phenolic ripeness. I am looking for darker brown pips rather than green astringent pips.

The 2019 harvest that has just taken place in Bordeaux is looking very good quality. However it will be very interesting to analyse the picking dates when I taste the barrel samples in April 2020. Some vignerons (such as Chateau Canon in Saint Emilion) went early to pick the grapes, whilst others (Chateau Clinet) waited a little longer. Both Chateaux make exceptional quality wines, but they have different philosophies for production. Did they pick early to maintain a fresh acidity and keep the alcohols lower or did they pick later to gain maximium phenolic ripeness?