1.4 Measuring grape sugar

Almost all winemakers use a refractometer to help them determine when to harvest. A refractometer is easy to use out in the vineyard and allows the winemaker to assess the ripeness of fruit.

A graph of grape sugar over time is hugely useful as ripening isn’t linear. Weather affects ripening, but you can still see trends in the graph – e.g. some varieties ripen faster but then sugar levels jump around so there is limited benefit from leaving them on the vines for longer.

Grape Sugar:Titratable Acid (TA)
Acids give crispness, brightness and thirst-quenching qualities to wines and are essential components to balance a good wine. There is a direct correlation between the amount of sugar present and the ability to make wine.

Ripening often isn’t linear, although over the years different clones/varietals having replicable ripening curves which is easily visualised using historical ripeness graphs. This is an extremely helpful tool when making decisions about when to harvest, as it can help you make an informed decision about how much the sugars may increase or the acidity will drop in the following weeks. Of course there are many other factors that come into play, so the more information you can have about ripening patterns in each block the better prepared you will be to pick the perfect time to harvest! You can also measure and visualise pH and the ripening process using the Ripeness Indicator Tool on your Sectormentor web app.

What to record

Record grape sugar reading

Make notes: Anything interesting you’ve noticed!



A smartphone (with Sectormentor downloaded)

Refractometer (with most models you need to calibrate the eyepiece first, which is super easy – instructions here.)