Grapes are for the birds

A host of words – especially on this site – are devoted to the characteristics and relative merits of the wines we drink.

Sometimes, though, it is instructive to switch our attention from “what” to “why”.

Getting to know more about a favourite subject is seldom a waste of time and can lead to better informed decisions.

Today, is one such opportunity – but it does carry a cautionary note with it.

For whom do vines primarily intend the grapes they produce? [Clue: Humblingly, it is not humankind].

If that warning has not deterred you, read on with this piece by MidWeeker Paul.

In it, he returns to his former “day job” of educating the young in the classroom or science lab.

He brings his customary enthusiasm, humour  and knowledge to the questions of ripeness and acidity in wine. 

Here is Paul’s “Lesson”.

“At times Brian likes to set me PhD level Science problems associated with wines.

His latest one was: “Are increases in sugar as grapes ripen co-incidental to reductions in acidity, or the direct conversion of one into the other”. Discuss.

Well as I often said to my Year 9 Set 4 pupils, always go back to basics.

Vines have tendrils because they want to climb up trees to the top of the woodland canopy

That way they can eventually entice birds to eat the grapes and, subsequently, disperse viable seeds; that helps ensure reproduction.

Ripe grapes were originally dark in colour for visibility reasons.

But timing is critical

However, the plant does not want the grapes eaten before the seeds are viable.

Consequently,  at first, immature grapes are hard and full of sour acid.

Through the ripening stage they become pumped up with sugar, water and the acid levels go down. Why? 

“To attract the birds when the seeds are ready – but not before, Sir.”

Well done, Jones at the back. Possibly Set 3 next year!

Looked at graphically

So in the classic ripening graph, sugar levels go up in a straight incline and acid levels go down in an angled straight line and we see a classic cross shape.

The temptation then is to jump to the conclusion that the acids are directly converted to sugars.

Jones, and you Davies, how many times I have told you to avoid temptations?

Now, pupils, a short lesson on organic acids found in wine grapes:

Here are seven of them

These are tartaric, malic, citric, oxalic, acetic, succinic and lactic acid; they have antibiotic and antimicrobial properties.

The main two – 90% – are malic and tartaric acids.

Right Jones, you have your hand up, what now?

“Sir, are these acids found in wines good for you?.

Well you normally try to divert me off topic and get me talking about Welsh rugby, but that is a cracking question, well done!

So, leaving rugby alone

As you will know, certain natural substances in food connect with harmful molecules in our body, helping to protect humans from damage.

But are these acids among them?

Well, some of them promote iron consumption and, specifically,  tartaric acid has positive effects on colon function while succinic acid has important implications for cardiovascular diseases.

Similarly,  malic acid has a role in gastrointestinal health and citric acid has a positive effect against diabetes.

Citric and malic acids also have a protective role on the heart muscle and act on ischemic lesions (damaged areas where blood flow is blocked).

But, after that diversion.

Now enough of digressions, let’s return to the main subject.

We have established that as grapes ripen there is a rapid increase in sugar content and a decrease in acid content and concentration – especially of malic acid.

Let’s look a little more at the details

It seems that véraison (essentially when grape skins change colour) is part of a complex process leading towards that sugar accumulation in the berries.

Around that time, the vine prioritises directing sugars towards the berries – although some are still used for the plant’s ongoing energy needs.

At the same time, though, malic acid in the berries is degraded to provide a further source of energy.

Some of it, however, converts partly into the less harsh lactic acid but, again, the processes involved are complex and depend on several factors.

So, to sum up.

In short, organic acids levels are radically scaled back during ripening but some do remain.

They provide the balance and freshness in the wines that your parents may enthuse over.

But, as we have seen, the rise in grape sugar levels and drop in acidity are actually parts of a complex series of changes.

In any exam question, good marks await those who describe them as “concurrent activities” rather than “a direct conversion process”.

Now gather around and I will demonstrate how to do titration properly and then you lot can have a go.”

Editor’s Note.

Thank you, Paul, for a delightfully crafted piece shedding light on a surprisingly complex subject.

Incidentally, Grapes picture by Junior Louis Jean on Unsplash and Feature picture by SHIV SINGH on Unsplash

After today’s glimpse at a broader picture, it’s back to my day job (budget but great value wine) in Monday’s Top Tip selections.