Now that harvest and fermentation is or soon will be underway for most of us, it’s a good time to be thinking about Residual sugar (RS), which refers to any significant concentration of sugars contained in wine, beer or cider at the end of fermentation. Winemakers and brewers are typically most interested in knowing the concentration of the fermentable hexoses glucose and fructose, the main reducing sugars; in some cases, sucrose may also be present. These determine the level of sweetness of the finished product.
If your goal is to make a relatively dry wine, you want to be sure it’s dry enough to be stable. At RS levels around 2 g/L (0.2%) or higher, an alcoholic beverage can spontaneously restart fermentation unless it has been properly stabilized, resulting in popped corks and fizzy wine. In some regions with warmer dry climates like California, Arizona, Eastern Oregon/Washington and similar areas, red varietals in particular are likely to come in at high starting sugar levels, like 25 to 27 Brix; these have the potential to achieve high alcohol levels that can inhibit yeast fermentation and leave appreciable RS, risking stability later on.
Measuring RS with the Vinmetrica Kit
The Residual Reducing Sugar (RRS) test , also known as the Rebelein or Gold Coast Method, determines the amount of residual sugar through a first reaction followed by a titration from a buret; it’s a pretty simple procedure that takes about a half hour, and multiple samples can be processed at the same time. The product listing on our web page is here:
https://vinmetrica.com/product/new-residual-reducing-sugar-assay-kit/
If I have a 27.5 brick Cabernet Sauvignon in primary fermentation, I am ultimately hoping for a sweeter dessert wine. I am in my 12th year of my making, and enjoying the experience. This 40 gallon batch of Cab is in my first attempt at a dessert wine. Would you have any links for me as to when to press, to end up with a sweeter wine? I am using a yeast that is tolerant of high bricks… RockPile 15 (RP 15).
Our Vin Metrica Pro continues to do its job for us.
Thank you,
Jim Todd
Jim, in your case that yeast might be able to take it all the way dry. You might Google “prevent complete fermentation wine” and see what you come up with. I believe the main choices are 1) cool the wine; 2) add distilled alcohol to bring the level up above what the yeast will tolerate (here, probably 20% ABV); 3) add sorbate/SO2 to stop yeast; or 4) sterile filter. If you don’t intend to make additions, then you should start tasting the fermenting wine when its specific gravity hits around 1.015 to decide if its residual sweetness is right. In all cases you have to decide which of these methods, or combination of them, you will use to stabilize the wine.
-Rich