Alcohol isn't added — it comes from the sugar in the grape
A wine's alcohol content isn't a number the winemaker "adjusts" at the end. It comes straight from a chemical reaction: yeast consumes the sugar in the must (measured in Brix) and converts it into ethanol and CO₂. The classic approximation — the same one LagarLab's engine uses — is the Gay-Lussac formula:
Probable alcohol (% v/v) = (Brix × yeast factor) / 1.05
The conversion factor runs roughly 0.55–0.60 depending on the yeast — a few real examples below.
This means the only ingredient that can raise or lower the final alcohol, before fermentation even starts, is how much sugar the grape had at the moment it was picked. And that depends directly on how many days it hung on the vine.
Why every extra day on the vine adds alcohol
As grapes ripen, they keep accumulating sugar day after day — it's plain photosynthesis, not magic. In LagarLab's model, for example, the Agrelo vineyard (Mendoza, Cabernet Sauvignon) opens its harvest window at 25° Brix, and every day the harvest is delayed adds roughly 0.35° more Brix. Ten days' difference in the pick date already shifts the starting point by more than 3° Brix — and that shows up directly in the final alcohol:
| Harvest timing | Brix | Probable alcohol* |
|---|---|---|
| 10 days before the usual date | 21.5° | 12.1% |
| Standard date (Agrelo) | 25° | 14.0% |
*Calculated with LagarLab's engine formula, EC-1118 strain (factor 0.59).
Almost 2 points of alcohol difference, without changing anything but the date on the harvest calendar.
The yeast strain also moves the number
At the same Brix, not every yeast converts sugar into alcohol with the same efficiency. LagarLab's strain catalog has its own conversion factor for each one — and the difference, while it looks small, is noticeable:
| Strain | Factor | Alcohol at 25° Brix |
|---|---|---|
| EC-1118 (S. bayanus) | 0.59 | 14.0% |
| BM45 (S. cerevisiae) | 0.58 | 13.8% |
| D254 (S. cerevisiae) | 0.57 | 13.6% |
| QA23 (S. cerevisiae) | 0.56 | 13.3% |
The harvest date decides the starting point (the Brix); the strain decides how efficient that conversion is. Both factors stack.
Why this is happening now, for two different reasons
What's interesting about 2026 is that the same phenomenon — picking earlier — is being pushed by two completely different forces at the same time:
- Climate necessity: 2026 saw some of the earliest harvests on record in the Northern Hemisphere, not by stylistic choice but by volatility — late frosts, heat waves, and drought forced many regions in the US, France, and beyond to bring the harvest forward simply to avoid losing the fruit.
- Consumer trend: at the same time, low- and no-alcohol wines are one of the fastest-growing categories in the market according to industry trade shows like Sitevinitech 2026 — picking earlier is, in itself, a direct way (without dealcoholizing afterward) to lower the alcohol content.
One force is reactive (the climate forces it) and the other is deliberate (the market asks for it) — but the chemistry behind both is exactly the same.
The limit: harvesting earlier isn't free
It's not simply "earlier is better": sugar isn't the only thing that ripens. Tannins, color, and varietal aromas follow their own phenolic ripening curve, slower than sugar's. Harvesting too early lowers alcohol, but it can leave tannins green and aromas underdeveloped. The optimal point depends on the style being aimed for — there's no single universal "correct" date.
Try the effect yourself
In LagarLab you choose when to harvest within each vineyard's real window, and see live how it changes the Brix and the final alcohol — before fermenting a single drop.
Enter the laboratoryFrequently asked questions
Why does harvesting earlier lower a wine's alcohol content?
Because alcohol comes from the sugar in the grape: the longer it hangs on the vine, the more sugar (Brix) it accumulates. Picking earlier caps that Brix, and with less sugar to ferment, yeast produces less alcohol.
How much Brix is gained for each day the harvest is delayed?
In LagarLab's model, each extra day on the vine adds about 0.35° Brix, within the normal ripening window. In practice it varies by variety, climate, and vintage, but the direction is always the same: more days, more sugar.
Does the yeast strain also affect the final alcohol?
Yes. At the same Brix, each strain converts sugar into alcohol with a different efficiency — for example EC-1118 yields more alcohol than QA23 from the same must, because its conversion factor is higher.
Why did 2026 see such early harvests in the Northern Hemisphere?
Because of climate volatility, not just heat: late frosts, heat waves, and drought pushed many regions to bring the harvest forward to avoid losing the fruit, regardless of any stylistic decision.
Does harvesting earlier always make a better wine?
Not necessarily. Before full phenolic ripeness, tannins and aromas are still green — harvesting too early lowers alcohol but can sacrifice complexity. It's a balance, not an absolute rule.