Fermentable sugar calculations

[richc]

I'm fiddling with some open source beer recipe calculator software trying to add the features I'd find useful. Compared with the calculators I am used to there is one thing I'm having trouble working out how to do, the estimation of FG. The simple calculation in the system at the moment just takes the maximum attenuation of the yeast and applies that to the OG. But, from my understanding, this isn't the only effect here.
The first effect, and the one I'm fairly sure other calculators compensate for is the amount of unfermentable sugars derived from speciality malts. Can anyone give me any pointers to how this sort of calculation can be carried out?
Secondly there is the mash temperature and profile, I'm putting this off until another day.

Thanks

 

[Aleman]

I normally ignore attenuation figures as I find them completely unreliable . . . . probably very reliable in a lab with a standard wort . . .plus there is a difference between apparent attenuation and actual attenuation . . .a rather large one

What I use is % fermentability of the grain/sugar/adjunct.

Sugar for example is 100% fermentable (and as its added to the mash tun is not subject to mash efficiency)

Base malt(s) are 65% fermentable (Pale /Lager/pilsner Munich/Vienna)
Crystal malts vary from 60% (carapils type, down to 25% for dark crystal /Belgian Special B)
Roast Malts around 20%.

As for effect of mash temp . . . good luck with modelling that one . . .again the effect is so variable as to be generally unimportant in determining a theoretical FG. Which is all that the brewing calculators can generate. Of course you run into the problem of the calculator said the FG is going to be 1.012 mine is only 1.016 why do they say this when I've lost 0.3% abv and not got a beer as strong as it say . . .. yada yada yada

 

[richc]

What I use is % fermentability of the grain/sugar/adjunct.

Sugar for example is 100% fermentable (and as its added to the mash tun is not subject to mash efficiency)

Base malt(s) are 65% fermentable (Pale /Lager/pilsner Munich/Vienna)
Crystal malts vary from 60% (carapils type, down to 25% for dark crystal /Belgian Special B)
Roast Malts around 20%.

Thanks for that, exactly the sort of thing I was looking for, are the % fermentability numbers standard (if so do you know where I can find them) or are they quoted per batch of grain (in which case I've never spotted them and must look harder).

As for effect of mash temp . . . good luck with modelling that one . . .again the effect is so variable as to be generally unimportant in determining a theoretical FG. Which is all that the brewing calculators can generate. Of course you run into the problem of the calculator said the FG is going to be 1.012 mine is only 1.016 why do they say this when I've lost 0.3% abv and not got a beer as strong as it say . . .. yada yada yada

Yea, I thought that was probably a second order effect, I might think about it when I get the basics done.

 

[pjbiker]

Yeah I guess it's suck it and see, experience with your own setup.
I've sent a pm to send you my brewing records as an excel file.

Also, on mash temperature see
viewtopic.php?p=132882#p132882