Impact of different gravities for the same ABV

Question

We can have the same ABV with diferents gravities. My reading for watermelon wine is:

1.064
0.997
=8.79%

However I found some recipes with readings like this to the same type of wine.

1.090
1.023
=8.79%

So I would like to understand the influence in the final product of starting with an higer vs lower gravity. I know the first example will be more dry than the second. What can we conclude more from the readings above?

Answer 1

I see two possibilities:

1. The second recipe has an unrealistic final gravity and most likely isn't finished fermenting. Fruit has very simple sugars, with final gravities typically 0.992 to 0.999 regardless of yeast strain used in most cases, so unless there was a more complex sugar added, or an unfermentable sugar like lactose or maltodextrin, the second recipe likely still has a ways to go and if bottled at that point would likely gush or explode.

2. It is also possible that a yeast with very low alcohol tolerance was used in the second batch. Some yeasts will quit fermenting at about the 9% mark, and this is close to what was achieved. If this is the case, the wine could be bottled with low risk of refermentation in the bottle. Better to be safe and allow an extra 2-3 weeks or longer prior to bottling just to ensure the gravity doesn't fall any lower.

Answer 2

With only two data points, the only thing you can conclude with any real confidence is that there is simply more dissolved sugar in a beverage with a higher finishing gravity.

In the above example (again it's only two data points), it could be suggesting this particular yeast tops-out at around 8.8% AbV, because the second set of readings still retain quite a lot of residual sugar the yeast could not convert.

The higher the concentration of sugars, the yeast has a more difficult job of processing, since the sugar puts osmotic pressure on the yeast's cell walls. So the yeast may have become stressed. Stressed yeast tends to produce more esters, so we could also infer that the first sample would have less yeast-produced flavours than the second one.

The yeast pitched into the second batch may have had very low vitality or viability, and/or simply gone dormant before the ferment was finished. This could also happen in the ferment became very cold, or very hot (hot enough to kill the yeast I mean). If some of these extremes happened, the yeast may also have undergone autolysis producing (awful) yeast-extract like flavours.

If this was a beer using "normal" brewers' yeast, and the gravity dropped really low, say close to 1.000 one would be wary to check that the batch had not been infected by another yeast (like Brettanomyces), wild yeast, or some bacterial culture that is able to convert the larger complex sugars that brewers' yeast cannot process.