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!

There are four fundamental traits that comprise a good wine and they all have to work together in balanced harmony. Previously we’ve explored Acidity, Tannin, and Alcohol . Let’s now take a look at Sweetness.

Sweetness in wine comes from natural grape sugars leftover after the fermentation has stopped. Or, by starting with overly-ripe grapes that produce a grape must which is so sweet that the yeast ultimately fails to convert all of it to alcohol. Perceived sweetness can also come from the alcohol itself, the toasted oak barrels used during aging, and simply from wines that are low in acidity.

The sugar that remains in wine is referred to as “residual sugar,” or RS, and is measured in grams per Liter (g/L). Here are the sweetness categories of wines:

Bone Dry is 0-1 Grams/Liter (e.g., Brut Nature sparkling wines)
Dry is 0-10 g/L (e.g., most red, white and rosé wines fall in this category, as do Brut & Extra Dry sparkling wines)
Off-Dry is 10-35 g/L (e.g., Off-dry Riesling, Gewürztraminer, “Dry” sparkling wines)
Medium-Sweet is 35-120 g/l (e.g., Madeira, Port, Moscato, Sweet Riesling)
Sweet if the RS is greater than 120 g/L (e.g., Tawny Port, Late-Harvest wines, Cream Sherry)
(Note: Coca-Cola has around 110 g/L)

In most wines, too much residual sugar results in a wine tasting sickly sweet. Conversely, if there’s absolutely no residual sugar, a wine may taste a bit harsh.

So, next time we’ll conclude this series by looking at how acidity, tannin, alcohol and sweetness must all be in balance in a really good wine. Until then, Cheers!