Finally, Fall is just around the corner and harvest time is beginning. This is the point where grape growers and wine makers become very focused on the grapes as they ripen. Then, once the grapes reach just the right level of ripeness, they are quickly harvested because, unlike other fruits, grapes don't continue to ripen once picked. So, you have to get it right.
If the grapes are picked too early they can be too acidic, too tannic and not contain the proper amount of sugar for a full and proper fermentation. Conversely, if the grapes are picked too late, the sugar level will be too high which can lead to an overly sweet wine. This is because fermentation will only go to the point where the yeast naturally dies due to the level of alcohol in the wine. So, the “residual sugar” doesn’t get converted to alcohol and remains in the wine.
The bottom line for grape growers and winemakers is to find the perfect time for harvest. While there is some science and chemistry involved there is also a lot of experience and intuition that goes into the decision to harvest the grapes.
Here’s a quick overview of some of the signs that the grapes are ready for harvest:
The Visual Appearance of the Grapes
From the experience and intuition categories, winemakers look for the exact color of the grapes to know when to harvest. The grapes may also take on different textures and levels of shininess versus dustiness as they reach the proper ripeness.
The Visual Appearance of the Seed Color
Winemakers also look at the stems and seeds as a sign of ripeness. As the grapes ripen, the stems will turn from green to brown. An un-ripe grape will have seeds that are white or green. When the grape seeds turn brown, they are nearing time for harvest. Winemakers may also taste the seeds. Unripe seeds can be highly tannic and bitter.
The Taste of the Grapes
It might seem obvious, but the taste of the ripening grape will also yield telltale signs to the winemaker. The grapes will have gotten mostly through the tannic and bitter stage and moved into being sweet. But again, the experience of the winemaker will determine if the grapes have just the right amount of tart and tannic qualities (that are very important in winemaking) while also having just the right amount of sweetness.
The Brix Level
From the science and chemistry side of things, winemakers will use a device called a refractometer to measure the ripeness of individual grapes. Brix measures the sugar levels in the grapes and allow a winemaker to convert that to how much alcohol the finished wine will have.
The Feel of the Grapes
Ripe grape berries (the individual grapes) are generally easier to pull from the stalks.
So, these are the primary methods used by winemakers to determine when the grapes are ready for harvest. A bit of science and a whole lot of experience goes into the final harvest decision. Cheers!