Most new brewers ask unanswerable questions or supply way too little information to get anything other than a guess as an answer.
Brewing is a science and an art but the art doesn’t make the science go away.
We can work out your OG (Original Gravity) pretty accurately, from an equation that says the mass of extract equals the Mass of wort times the Extract (everything soluble) content, we express this as oP (Plato) which is %WW (mass of solids as a % of total mass).
We can get the total mass by V (Volume) times SG or to put it into one equation; Volume (20L) * SG *oP, well after we rearrange the equation and it’s handy to know that the SG is roughly = (4*oP)/1000+1.
It’s really easy if you put the equation into a spreadsheet then use the goal seek function to find the OG.
As we know the Volume (20L) and the mass of extract from:-
LME (Liquid Malt Extract) is ~80% solids, so the mass of extract in the kit would be 1.7kg*0.8=1.36kg
If you added the 500g as a dry product it will be close to 500g of solids
500g of Sugar (Sucrose) would add 500g.
500g of LME would be again ~80% solids.
500g of Dextrose would be 91% solids.
500g of "brewing Sugar" is a mixed bag, well that can get interesting.
If we assumed that you added 500g of Sugar, which will give us a fair stab at the highest possible alcohol content.
We Have 20L and 1.86kg of extract... I have gone off and done this in Excel... SG is 1.03591031527199, let’s call it 1.036 and/or 8.98oP (same thing really).
We approximate the ABV by (OG-FG)/7.5, as the 1.000 part of SG is just times the equivalent mass of water, not a real unit; we can’t use it in calculations. We could use oP or as most home brewers do use Points, just treat the three digits after the decimal as a number so we would say the OG 1.036 was 36 Points
As we don’t have an FG yet, all we can do is take a stab.
Let’s assume that you will get 80% attenuation, remember that 80% is the same as 80/100 or 0.8 in an equation
From that rearrange the equation to get an approximate FG
We need the Change in gravity so 36*0.8=28.8
The ABV will at most be ~28.8/7.5=3.84%
Most likely to be a bit less as you haven’t used Sucrose.
Your target 3.5% ABV won’t be too far off. I would use DME (Dry Malt Extract) as it will give the most flavour and the alcohol content you are looking for.
Next time think about the information that’s needed to answer your questions, will make life easier for everyone.
Mark
