Fermentability of Malts

[Jimmy Orkin]

I have been using Promash to predict the Final Gravity of my beers. I was taking OG * (1 - average apparent attenuation %). This assumes that all the sugars in the OG are fermentable. That is not the case with some of the specialty malts.

This might explain why I do not get the as low a FG as I was calculating.

Does anyone know how to calculate the fermentability of wort given a mix of malts in the mash?

[Bill Lawrence]

Well, I really don't know how to calculate it but I just throw the yeast in there and then let them do their thing. To tell you the truth, I don't even bother measuring finishing gravity any more and haven't for several years now. I just wait for the stuff to stop bubbling then rack it to a secondary fermenter. I do however taste it at some point before I keg or bottle it it so I guess you could say that I use the "Willy hydrometer". By the way, I would think that predicted attenuation would involve the % of malt adding unfermentable sugars in the grist, the mash temperature as well as the yeast strain used. Consider the extreme example, a beer mashed really hot to obtain a dextrinous wort with alot of crystal malt using say the Fuller's yeast strain as compared to exactly the same wort but fermented with Brett, one will have a pretty high terminal gravity while the other will end up bone dry (assuming of course you wait long enough). As a guess, I would expect that in a normal situation you will end up with roughly 20% to 25% of your original gravity but at the end of the day, I'm going with the "Willy" test every time.

[BigWally]

I don't know that I want to drink anything that the Willy hydrometer has been in ;->

[RyanWeary]

Here is a website I use when I'm designing beers:

http://hbd.org/cgi-bin/recipator/recipator

In fact I used it last weekend to create an Imperial IPA and I hit everything on the nose. Now, as long as my yeast ferments all the way through, I should hit my predicted FG of 1.012 - 1.014. If that happens, it'll actually be the first time everything went perfectly from start to finish.

[Jimmy Orkin]

A guy in the Homebrewtalk forum did a test. His results are at the end. Pretty interesting.

http://www.homebrewtalk.com/f128/testin ... lt-208361/