So, do you really want to know how many calories are in that wine you are drinking?
If you do, I hope you have access to two important pieces of information: the alcohol by volume and the total residual sugar. The ABV must be, by law, printed on the bottle – but there is also a lot of flexibility with regard to how precise that labelling is. Generally, it is possible to be off by a half a degree – sometimes more. And there is no law anywhere that says the residual sugars need to be listed. Nevertheless, this information can often be found on producer websites, and we can get a good ballpark figure for the calories of our favourite bottle.
But why am I even doing this? Because I love sweet wine, and I got tired of people talking about all the calories that these wines have – as if normal wines were calorie-free. Alcohol has calories, sugar has calories. I can understand if you are diabetic – and if you are, I am very sorry. But if you are worried about how many calories are in your wine, perhaps you shouldn’t be drinking alcohol at all. Just saying. At any rate, sugar needs to be fermented into alcohol, so I wanted to know what the calorie difference would be if my beloved sweet(ish) wines had been fermented dry, hypothetically.
Here’s what we know:
Ripe grapes have a number of different sugars, including unfermentable ones like rhamnose, arabinose and xylose, but these are in very small amounts. Partly for this reason, no wine can ferment completely dry; there will always be a little residual sugar. The main sugars in ripe grapes are glucose and fructose. Normally glucose dominates, but sometimes – particularly in very ripe grapes – the balance can shift to fructose. Fructose tastes sweeter than glucose. Not that this matters for my purpose, because the calories are the same: about 4 calories per gram.
Alcohol, on the other hand, has 7 calories per gram. So alcohol, by weight, is more calorie-dense than sugar. But it takes about 17 grams per litre of sugar to ferment into one degree of alcohol/litre in the finished wine. With these numbers, the math becomes relatively simple.
The Work
Let’s use a sample bottle – and the inspiration for this post – to calculate calories. The inspiration was my new favourite Riesling from Rheinhessen: “Hölle” Saulheimer Riesling Kabinett vintage 2018 from Weingut Thörle. This wine has 10% alcohol by volume and a residual sugar of 37.6 grams per litre. And it is freaking amazing. I wrote about it and others earlier today in my post about summer wines.
First find out how many grams of alcohol there are in your standard-size wine bottle. This will be done in millilitres, of course, and it is important to remember that alcohol weighs less than water of the same volume. The specific gravity of pure alcohol (no matter whether ethanol or methanol) is 0.79. That means that alcohol will weigh 79% as much as the equivalent volume of water.
Alcohol in milliliters:
10% abv x 750 mL = 75
Alcohol by weight in grams:
75 mL x 0.79 = 67.5 g
Calories from alcohol:
67.5 g x 7 = 472.5
So this wine has 472.5 calories from alcohol. How much is the residual sugar contributing?
Calories from unfermented sugar:
(37.6 g/L x 0.75 L) x 4 = 112.8
Okay, so if you drink THE WHOLE BOTTLE, you will be getting 585.3 calories. But here’s where things get interesting. What if the wine had fermented dry? What would the potential alcohol have been, and how many calories would it have?
Potential additional alcohol by volume from unfermented sugar:
37.6 g/L ÷ 17 = 2.2% abv
So the potential alcohol of this wine was about 12.2% abv. What would the potential calories have been for this bottle, had the wine been fermented dry?
((12.2% abv x 750 mL) x 0.79) x 7 = 506
Okay, in this case, it’s a difference of 80 calories for the entire bottle. Not particularly significant. For a decent pour of 187.5 milliliters, that’s a difference of 20 calories with this wine.
Now we know! Use your power wisely. Drink responsibly, don’t overdo it too often. But when you are drinking wine, enjoy it.