There's a spec sheet that comes with each bag of malt and right near the top of the sheet, usually, underneath color and gravity per pound is extract efficiency, brewers grade malt extract efficiency is 83%.
A spec sheet exists because malt is very inconsistent and because it's inconsistent it's tested and the test results are list on the sheet. The sheet is used by a brewer to determine if the malt is suitable for making ale and lager (under modified, low protein malt, decoction method), or more suitable for making whiskey (high modified, high protein malt, single infusion method).
An expensive apparatus is used to determine efficiency. The apparatus, also, determines attenuation and ABV. A formula hooked to a couple of hydrometer readings is not accurate. I find it hard to believe that a computer generated group of numbers are accurate time after time due to the inconsistency of malt. Same thing with recipes.
Malt high in percentage of protein, slack malt and poor crush are responsible for low efficiency. Percentage of protein is listed on a spec sheet. Modification (Kolbach, SNR) is listed on the sheet.
When mash is rested at 66C, Alpha produces mostly glucose, and some sweet tasting, non-fermenting sugar from simple starch, amylose. Yeast should have ripped through the sugar during primary fermentation cranking out alcohol, FG should have dropped very close to expected FG after 10 days.
When a recipe for ale and lager recommends; high modified malt, single infusion, primary fermentation, no secondary fermentation and sugar priming or injecting CO2 for carbonation, aged/lagered for eight to 10 weeks, the beer will be similar to Prohibition style beer.
To produce ale and lager a Beta rest is needed. During a Beta rest conversion occurs, Beta amylase converts glucose into maltose and maltotriose which are complex types of sugar. Yeast works well with glucose, not so well with complex sugar, for that reason secondary fermentation is needed.
Check out recipes on Weyermann Malt website.
