There is no single definition when grapes are considered ripe, or in other words, when to pick grapes for wine making. What a wine maker will consider “ripe” will depend on the grape variety, the location grown, the wine making style, etc. What my neighbor considers ripe I may not, and vise-versa. Our wines will be different. And there is nothing wrong with that.
In fact, the topic of ripeness is so complex, I will simply defer the bulk of the description to an external link about ripeness.
However, in a previous post I said I would comment on acidity in wine, and will do so now by showing how one simple measure of acidity can be used to help determine potential ripeness. Note: Acidity is also a complex topic that I will defer the gritty details about also to an external link.
To make this calculation you need an accurate way to measure pH such as can be done with a pH meter (pH paper is not accurate enough).
The process is rather simple: sample grapes from the vineyard (I am using some Italian Riesling in this test), crush them, strain the juice and plunge (gently) the pH meter into the juice and read the value.
And for the same wine sample measure the Brix:
With the values of pH=3.0 and Brix=19.6, we apply some simple math which is pH squared times Brix. Or simply:
3.0 × 3.0 × 19.6 = 176.4
The rule of thumb here for a white wine (like my Riesling here being sampled) is potential ripeness occurs when the value is closest to 200 (considered the “optimal” value). Since the calculated value is only 176.4 the wine would not be considered ripe, and it should be left to hang on the vines a bit longer. For red wine lovers, you can use the same metric by comparing the value not to 200 but to 260.
One would repeat the process every few days until the optimal value is reached, after which one may consider the grapes ready to harvest.
Ready to harvest, yes, but not necessarily ideal to harvest. One must keep in mind what I expressed above: ripeness is a complex topic.
Thus, this measurement is just a simple way to know when you might start to consider harvesting. Indeed, there are other tests for acidity and ripeness that one can (and probably should) do to help narrow down the best time to actually start to harvest. For example, you may decide to wait, allowing the grapes to develop more complexity. How much longer you actually wait after the “suggested” time to harvest is up to you and for the style and type of wine you want to make.
For example, in colder climate areas (such as ours) I could ignore this value, wait 3 more months and harvest the grapes to make a Christmas wine: the freezing temperatures dessicate the grapes, concentrating the sugars and allowing for the potential to make a very sweet dessert wine. Or in the case for us this year, we decided to harvest our Pinot Gris (Szürkebarát) grapes with the following pH and Brix values:
3.2 × 3.2 × 20 = 204.8
204.8 is very close to the “optimal” value. But I would have liked to give the grapes more hang time to get the sugars up. But a week long heat wave was being predicted and the chance this would have sent the acids too low, resulting in a flabby wine with little character, was a real possibility. So the call was made to pick earlier than later, since acidity is a more distinctive feature of this wine than the alcohol content.
Farming and wine making…. Decisions…. Decisions……