Extract fermentability

My last partial batch used Laaglander extract (I thought it was Munton's, which is what I usually use). I hit my predicted OG dead on, but after three weeks, I was still about 12 points above my calculated FG. I didn't understand it at first, because I had a good strong fermentation. It was at that point that I discovered I'd used the Laaglander extract--it's notorious for its comparatively low fermentability.

I didn't really have a problem with the higher-than-expected FG, but I would have liked to have known this before I brewed the batch. As it is, the program only has one "generic" extra-light dried malt extract (and other extracts, for that matter). I was going to make duplicates of that "Grain/Extract" entry, and then change the fermentability of it to match my FG (predicted FG was 1.017; I ended at 1.028 instead). I discovered that none of the options under the grain/extract parameters allow you to change this. I don't plan on brewing with extract much longer, but for anyone who does, this is good information to be able to change. I've found resources that list Laaglander's apparent fermentability as 55%, while Munton's is closer to 75%. Any possibility of this?

Well this one is a little tough to do because there are so many factors that enter into determining the final gravity.

At the moment BeerSmith uses the yeast attenuation to estimate the final gravity, which gives a reasonable estimate if the yeast is used for the appropriate style.

Unfortunately to accurately predict final gravity one needs to take into account a dozen other variables including mash temperature, fermentation temperature, percent of specialty grains used, fermentability of each grain and so on.  Even worse, there is no data I am aware of that quantifies the effect of each of these factors, so one is again left to estimating.

I could add apparent fermentability for malts and somehow average it into the final gravity calculations, but I would need a source for fermentability of all the malts to make it valuable.  Do you have a good reference?

Cheers!
Brad

Basically, I'm only looking for this for extracts---not for grains. Obviously, it's hard to pinpoint an exact FG because of all the variables you listed, but the production techniques used for different extracts leads to different rates of attentuation. For instance, Laaglander (the extract I used on my last batch that didn't finish as low as I hoped) has a lot of unfermentable dextrins and what-not. Munton's, which I typically use, is much more fermentable. I've hit my predicted FGs dead-on or within a couple points most times I use Muntons, which seems to have an attentuation similar to what BeerSmith's generic extract defaults to.

Obviously, the actual values would require research, or at least talking to the folks that produce the stuff. But having an editable field for "percent fermentable" would allow one to track trends, if they use the same kind of extract each time. I know it's a long shot, but would help prevent that "oh nuts, my beer didn't finish" exclamation