[BrodyR]

So today I was messing around in BeerSmith and realized that when you add sugar to a recipe the estimated final gravity decreases.

I was aware that subbing out some malt for sugar would lead to a lower FG as it completely ferments but it surprised me that it would actually decrease the FG. Is anyone able to explain the logic behind that? I'm also wondering if this explains why sometimes my beers are a couple points lower when opened than they were at bottling time before being primed.

[erockrph]

The specific gravity of ethanol is less than water. If you're adding table sugar to a recipe, you can assume that it will ferment out completely. This leaves you with the same concentration of unfermented sugars (from the malt), but more alcohol in solution than if you hadn't added the sugar. Since there's more alcohol, the SG will be lower.

[dmtaylor]

If you SUBSTITUTE malt for sugar, then final gravity will decrease.  This is because you've gone from something 65-75% fermentable to 100% fermentable.

But if you were to ADD sugar to an existing recipe, the result goes more like this:

Adding sugar increases the original gravity, but the final gravity will most likely stay the same, or perhaps will decrease by like 1-2 points, maybe, but not that anyone would really notice.  For example:

You have a 1.060 original gravity beer, with an expected final gravity of 1.015.  If you ADD a pound of sugar, your original gravity might go up to 1.070, something like that, while your final gravity stays the same or maybe goes to 1.014.

The result is... more alcohol, with zero impact on the flavor except the greater alcohol.  You've gone from a 6% ABV beer to a 7% ABV beer.  The body and mouthfeel might feel slightly thinner but most likely won't be impacted very much at all.

[Joe Sr.]

If you SUBSTITUTE malt for sugar, then final gravity will decrease.  This is because you've gone from something 65-75% fermentable to 100% fermentable.

I think you mean substitute sugar for malt.

Other than that, I agree with you.  I will typically use sugar instead of more malt in a big beer to help it finish drier.

[BrodyR]

"The specific gravity of ethanol is less than water"

That makes a lot of sense - I suppose that's why Cider can finish out below 1. Interesting, thanks for the responses everyone.