Calculating Residual Sugar and Final Gravity

[braidenlowe15]

Okay so I'm a mead newb but ive done my fair share of research and have background knowledge on the scientific process of fermentation and sugar consumption with yeast.

I've come across a few seasoned mead makers on the forum who are able to look at a recipe and calculate the residual sugar, abv, and final specific gravity that will result after fermentation is complete.

Can yall please provide me with these equations? I'm trying to create my own recipes and want then in the semi-sweet range. I also might try a sparkling mead, but I don't want to kill the yeast with too high of an alcohol level. Most will end up as melomels, metheglins, or somewhere between the two.

 

[loveofrose]

The Mead Calculator below should give you everything you need. I personally use an iPhone app called BrewPal.

http://gotmead.com/mead-calculator.html

I generally look up published ABV tolerance of yeast and add enough honey to reach that tolerance. Once the gravity is stable at 1.000 (sometimes higher, ABV tolerance is more of a ballpark figure), I'll add honey to my desired gravity and let it try to ferment it. Once again, calculate how much to add. Repeat if needed until stable.

For Sparkling, you better hit 1.000 and add primer sugar. Or force carb in a keg.

 

[braidenlowe15]

Can you please explain how you know how much honey is needed to reach the yeasts tolerance and why does it need to be stable at 1.000?

 

[braidenlowe15]

Also, that calculator is broken. It won't calculate once filled in. Seems like the webpage is broken

 

[loveofrose]

Ok. Let me back up. Your hydrometer measures how much sugar is in water. Water normally has a specific gravity of 1.000. Increasing amounts of sugar raise this gravity. As the yeast eat the sugar, the gravity lowers. If the gravity hits 1.000, then you are back to mostly pure water. At this point, there is no more sugar to eat, therefore your gravity is stable. In some high alcohol mead cases, the gravity can go below 1.000. This is because the gravity of pure ethanol is 0.794 which causes a slight drop in waters gravity. Personally, I've never seen below 0.980 in mead.

I generally use gravity calculators such as this one:
http://www.brewersfriend.com/abv-calculator/
(Yes, this one works.)

As a quick guide, some common yeast ABV tolerances and SG that would end at 1.000 to reach that %ABV:
10% - 1.076
12% - 1.092
14% - 1.107
15% - 1.115
18% - 1.138

Also, 4 ounces of honey in 1 gallon (final volume) will raise the gravity from 1.000 to 1.010. Eight ounces 1.020 and so on.
This is how you determine how much honey you need to reach your desired gravity.

Does that cover it?

 

[braidenlowe15]

Ok that's where you lost me! I didn't realize you were talking about water it 1.000 gravity. That cleared it up perfectly.

I have one more question though. How are people predicting abv? To get abv you have to predict the final gravity as well. It seems like there are too many variables to be able to predict something like that such as your honeys water content, yeast strain, temperature, oxygen, etc.

I know that you can assume a 0.100 drop on gravity. Is that where the predicted abv comes from?

 

[loveofrose]

Predicted ABV comes from the company you purchase the yeast from. With a properly managed ferment, you will hit the minimal tolerance. I often surpass it because I follow the fermentation management in my article (see signature). If you haven't, read the article and hit me with more questions.

Edit: in case you cannot see the sig:
See my Current Mead Making Techniques article here:
https://www.homebrewtalk.com/current-mead-making-techniques.html

 

[braidenlowe15]

Thank you so much! That was extremely informational

 

[stann]

ignore this. can't see delete option

 

[stann]

so if we know the abv and FG , say 14%abv, 0.8 = gravity ethanol

0.14 x 0.8 = 0.112

+ 0.86 x 1 = 0.86

0.112 + 0.86 ~= 0.972

but FG is 0.990

does the difference, 0.018, give us RS?