Residual Sugar in Wine

Dear Tim,

I love your Master Vintner™ wine kits, and really like the wine I'm making with them. I've recently started exercising, and I've gone on a ketogenic diet and I want to figure out how many total carbohydrates there are in my wine Master Vintner™ Sommelier Select Old Vines Merlot. Can you provide a chart on all of your kits? Also, is there a way to test my other wines to see how much sugar they have in them?


PK in GA

Good luck on your diet—wine is an important part of a gracious and tasteful lifestyle, and I'm glad you're including it as a part of a healthy regimen that includes exercise and a balanced diet.
We can't actually provide you with a list of total carbs in finished wines for Master Vintner™ kits—not because we don't have a good idea what it will be, but because those kind of declarations have legal meaning for food products (which kit wines are) in the USA.
Claims about total carbs need to be certified and measured for the finished product, which means that depending on how your fermentation went and how low your SG hit at bottling, yours might be different from another identical kit, and suddenly the FDA is asking us pointed questions about accuracy of our declarations. Really, they have no sense of humor.
But I can give you some guidelines for what you can expect from any dry wine that you make. Unless you add sugar to a kit after fermentation it's going to have between zero and ten grams-per-litre of sugar. That is to say, in one bottle of wine you could have between none and 7.5 grams (one and a quarter teaspoons) of sugar.

Sugar has 4 calories per gram, so the max for a dry wine is going to be 30 calories from sugar per bottle. Not bad, and depending on how genic your keto is, probably within the realm of your dietary restrictions. One five-ounce glass of wine at ten grams per litre would have 1.5 grams of sugar, or six calories—seems doable.
Any wine that you add a sweetening pack to, or any wine that you add the recommended amount of wine conditioner to is going to get another ten grams of sugar per litre, so double the numbers for sixty calories per bottle from sugar, and 3 grams, or twelve calories per 5-ounce glass. Still doesn't seem too bad if you don't overdo it and drink the whole bottle.
Beyond that it's only guess how much sugar various wines have in them, but it's obvious that dessert wines and intentionally sweet varieties are probably off the keto menu.
There is a way to check your wines for residual sugar. For many years winemakers used a product called 'Clinitest', which is designed to test for reductive compounds in . . . well, in urine, mostly. The test caught all types of sugar and could tell the tester things about blood sugar, etc. Bayer, the company that made the test tablets discontinued them, but there's a replacement product out there called 'Aimtabs', and it works the same way: you put ten drops of wine in a test tube, add a tablet and shake it up, waiting for a color change. Compare the change to a chart and it will tell you exactly how many grams per litre of sugar you have. There are slightly different procedures for wines with more than ten grams per litre, but it's all basically the same. A quick web search should turn these up, and with a little math you can figure out how much residual sugar is in your wine with decent accuracy.
Always remember to take your hydrometer readings as well: if your kits are consistently turning in higher numbers than the recommendation in your instructions, double-check your must temperatures before yeast pitching and during fermentation, and make sure you're adding your yeast nutrient when directed.