Beer Strength!

[Old Jake]

Having read various threads, I still don't quite understand the basic process of what defines alcohlic content. I understand how to calculate it by using the difference between OG and FG and diividing by 7.36 (from memory!)

What I don't understand is why? Is it simply to do with the amount of sugar used and how it reacts with the yeast.

I've also seen on other threads where various brews have been made and it seems that from the OG you can calculate what the FG should be. How?


I've posted it in this forum because I do only use kits so need a response appropriate to my level of understanding!!

cheers

OJ

[steve_flack]

That's basically it yes. The maths comes from the fact that the sugar is consumed by the yeast producing carbon dioxide (which escapes as a gas) and alcohol. Alcohol is less dense than water so producing it and using up the sugars makes the beer less dense. The 7.36 (sounds about right - I haven't checked) is the magic number that accounts for this. Of course not all the sugars are fermentable so that's why the FG is still more than that of water.

You can work out the FG from the OG as most yeasts appear to convert 3/4 of the OG's sugars (so a 1.040 beer will go down to 1.010). There are several other factors involved and this only works for an allmalt beer. If you use a lot of table sugar then the FG will be lower as all the table sugar is converted to alcohol leaving no residual unfermentable sugar.

[Andy]

The yeast feeds on sugars present in the wort (unfermented beer) and produces alcohol. The more sugars present the more the yeast will turn into alcohol Certain types of yeast tolerate alcohol better than others so some will give up the job when the alcohol %age reaches a certain level other yeasts will keep working for a bit longer...

[AT]

The yeast feeds on sugars present in the wort (unfermented beer) and produces alcohol. The more sugars present the more the yeast will turn into alcohol Certain types of yeast tolerate alcohol better than others so some will give up the job when the alcohol %age reaches a certain level other yeasts will keep working for a bit longer...

Like a duracell battery?