Four things contribute to conversion and fermentability. Mash thickness, pH, time and temperature. You can throw crush in there, too. A thinner mash converts quicker than a thick mash. But a thick mash preserves enzymes for a longer period of time. Most home brewers use 1-1.5 qts/lb. That is the way the English do it. Germans use 1-3 qts/lb., they have their reasons. A thinner mash increases maltose and wort attenuation. The pH is important. If the pH is out of the optimum pH band of a & b enzyme, they become sluggish. Temperature solubolize and gelatinize starch. There are four enzymes that work on starch conversion. The a & b amylase, maltase and dextrinase. The enzymes don't necessarily make long or short chain sugar. What alpha enzyme does is liquify the starch into carbohydrates and amylose by taking the long chain starch and breaking it apart. The long chain has a reducing end and a non reducing end. Beta amalase can only break down the non reducing ends of the chain. Beta is responsible for forming fermentable maltose. What causes the non fermentability of wort is limit dextrins. The limit dextrins are at the branch "Y" after the amylose is broken down to amylopectin. They are a-limit dextrines. There are b-limit dextrins, too. Alpha enzyme produces maltriose. It is needed in lagers to allow for a long cold aging process. It also, produces some glucose which ferments and the a-limit dextrins that are non fermentatable....You may have had the right mash thickness, pH, temperature and a good crush that allowed a lot of starch to solubolize and gelatinize. Giving the enzymes a lot to work with, creating a higher OG and a lower FG from a lot of maltose and glucose. I don't know if you use iodine to check for conversion. If you do, next time pull out some mash and squeeze out a teaspoon full or more of liquid onto the plate, put a drop of iodine on the liquid. If it turns black, a lot of starch was stuck in the husk, not being converted. Make sure there are no husks in the sample. Husk will turn black regardless. The Germans decoction mash. The method produces higher gravity, more yield and a lower FG. I was a bagger until about 1985 when the company making decent bags went out of business. The method was becoming boring, anyway. By 1987 I burned out as an infuser. Since then, I tri-decoction lager and pils and once in awhile a German ale. Decoction method gives a brewer more control over the final product.
