If you’re a wine enthusiast and regularly visit tasting rooms, chances are you’re familiar with tasting terms such as “blend,” “vintage,” or “nose.” But there are other interesting terms that wine drinkers are less likely to encounter that nonetheless play an important role in winemaking.
Brix, a measure of sugar that can help a winemaker determine a grape’s ripeness, is one such term.
Brix is colloquially described as “degree Brix” and written as “°Bx.” Each degree represents one gram of sugar per 100 grams of wine.
A riper grape has higher sugar levels, which indicate a higher alcohol content, a sweeter taste, and a fuller body once that grape is turned into wine. Some styles of wine — such as dessert wines — require riper grapes than others.
For some varieties, less sugar and more acidity is desirable. Often, winemakers want grapes with a balance of these two qualities.
“When grapes ripen, sometimes it’s at the expense of the natural acidity that’s in the fruit,” says Sean O’Keefe, winemaker at Mari Vineyards on the Old Mission Peninsula.
In order to judge how their wine will turn out, winemakers measure the sugar content of their fruit by reading its Brix level.
Each winemaker has their own method for measuring Brix. If they want to estimate when to harvest their grapes, one winemaker may pick individual grapes for measuring at random, while another may carefully pick multiple grapes from representative parts of the vineyard to account for their different ripening rates.
Measuring Brix involves refractometry, a method of analyzing how light refracts through a substance. A common instrument used for this measurement is the aptly named refractometer. (Less commonly, a winemaker might use a portable densitometer or a mass spectrometer in a lab for more accurate — and much more expensive — measurements of individual sugars, such as glucose and fructose.)
O’Keefe explains how the refractometer works: “You put a little drop of juice onto a glass slide, and then the way that the light refracts off it will tell the meter how dense it is.”
The density of the juice offers important insight for winemakers.
“What you’re actually measuring is dissolved solids — or soluble solids — in the liquid, but the major soluble solid that Brix is measuring is sugar, so it roughly equates to percent sugar,” says Brian Hosmer, winemaker for Chateau Chantal and Hawthorne Vineyards on the Old Mission Peninsula.
To extract juice from the grapes, a winemaker might mash the grapes in a baggie and squeeze the juice out onto the refractometer. Or, if a winemaker is measuring Brix after harvest to monitor how the grapes are fermenting, they will pull a sample from the tank.
While many winemakers prefer using the common grams-per-liter measurement over Brix when describing leftover sugar in the wine after fermentation, Brix — along with factors such as acidity, pH, skin coloring, and more — is vital to measuring the wine’s potential character while it is still a grape, judging when to harvest, and determining whether a fermenting wine needs added sugar.