Final Specific Gravity

updated 06/09/2026

A common topic of discussion is, “how do I know when my wine is ‘done’?”.

The commonly accepted answer on WMT is, “When the SG is less than or equal to 0.998 and is stable for 3 days”.

The next question is, “Why?”. That is the focus of this post.

What Is Specific Gravity?

Specific Gravity (SG) is the relative density of a liquid with respect to distilled water. The SG of distilled water is 1.000. [This varies with temperature, but for our purposes the value is a constant.]

Wine is composed mostly of water, with a varying percentage of alcohol and other components (pigment, color, & flavor). The SG of methanol is 0.787 (according to the source I used), so the presence of alcohol reduces the SG of the wine below 1.000.

In my wines, I found that the Final Gravity (FG) has varied between 0.990 and 0.998, about 99% of the time. I’ve had a few wines that finished between 0.999 and 1.002 (more on these below). Most whites and light fruits are between 0.990 and 0.994, while reds and dark fruits are typically between 0.994 and 0.998.

Why Does Specific Gravity Vary?

The SG varies for 3 different reasons.

1. The amount of alcohol. The higher the ABV (Alcohol By Volume), the lower the SG.
2. The amount of other “stuff” in the wine.
3. Any remaining sugar.

For the purposes of the remainder of this post, we are ignoring residual sugar. This complicates the discussion without adding anything useful, so let’s consider dry wines (no remaining fermentable sugar).

We know the volume of the wine. We can measure the part of that volume that is alcohol, although getting an accurate answer takes extra measures (not discussed here).

What we don’t know is the amount of other “stuff” in the wine. Sure, it’s possible to do a complete analysis of the contents of a wine, but very few of us have access to a laboratory that can do that. Let’s accept that the other “stuff” exists.

If looking at just the ABV, a heavy red with at 15% ABV should have a lower FG than a light white wine at 10% ABV. It has more alcohol, so the FG should be lower, right?

Nope. It’s the other “stuff” that changes that. Keep in mind that heavy reds have a lot of pigment, and aroma & taste are also particles. SG is a measure of the density of the liquid as a whole, NOT the density of just the water and alcohol. As a result, heavy red wines typically have a higher FG than lighter whites.

Exceptions To The Rule

All that said, I’ve had wines finish between 0.999 and 1.002. Why?

I cannot provide a definitive answer. I have an understanding of the parts, and practical experience, but that doesn’t provide a conclusive answer, just conclusions based upon what I think I know. Following are my thoughts.

1. Unfermentable sugars. Not all sugar types are subject to consumption by wine yeast. Dry red wine may contain around 1 g/liter of unfermentable sugar. Other wine types, especially those that are made from commercial juice-type products, may have more.
2. High quantities of pigment, color, and flavor particles. Home winemakers don’t have a way to test such things, so we have no idea what’s there.
3. “Stuff” in kits. I’ve had a few kits finish with high FG, and this may be an artifact of the process that produces grape concentrate. This is a guess on my part.
4. Mother Nature and Dionysus like messing with mortals. This is a humorous way of saying there are likely other factors we do not recognize and as such, cannot account for.

There are things we simply cannot control. In 2019 I had 17 gallons of a second run red wine, which stopped at SG 1.000. I added a fresh yeast starter with EC-1118 (which will ferment a rock if given the opportunity), and more yeast nutrient. Nope. Didn’t budge for over a month.

I had just purchased a used 55 liter barrel (14.5 US gallons) and moved most of the wine into it. For nearly 3 months it was fine.

Then the bung blew, 3 days in a row. I drew a sample — SG was 0.992. For reasons beyond my understanding, fermentation kicked in during the coldest part of the year Why? I have absolutely no clue. So I cite Mother Nature and Dionysus.

Conclusions

My biggest advice to every winemaker is to never rush to bottle. Another month will not hurt anything. And it’s free. If anyone has to unbottle a batch because fermentation in the bottle, it’s both a hassle, and it’s an expense, as all the corks need to be replaced. If labels and capsules have been applied, that’s more expense.

As I always say, Patience Grasshopper.