Mashing at 157F produces a sweet wort because Alpha releases more sweet tasting, non-fermenting sugar than glucose at the temperature. The types of sugar are contained in amylose, simple starch. Glucose is simple sugar, a yeast favorite.
Body and mouthfeel are the result of A and B limit dextrin which are tasteless, non-fermenting types of sugar. Dextrin is wrapped up in amylo-pectin which is heat resistant, complex starch that makes up the tips of the kernel, it's the richest starch in the kernel. When Alpha liquefies the starch dextrinization occurs. The temperatures used during infusion mashing are not high enough to cause enough of the starch to enter into solution before Alpha denatures and the starch is left in the spent mash. It's the small, white particles noticeable in spent mash. In the decoction method mash is boiled and the starch rapidly enters into solution.
Resting mash at 145 and 152F causes a couple of things to occur. When mash is rested at 145F conversion takes place and during conversion Beta converts glucose into complex types of sugar, maltose and maltotriose. Alpha is active at the same time releasing glucose (saccharification) for Beta to work with. When a Beta rest is used secondary fermentation is needed. The beer will not require sugar prime or CO2 injection because during the aging and clearing phase the beer will naturally carbonate due to maltotriose. However, without dextrinization the beer will be thin and without a short rest above 155F the beer will lack sweetness.
When mash is rested at 152F none of the above applies, except for the dextrinization part because it is important in 152F beer. Single fermentation works no problem with 152F. The beer will be similar to Prohibition style beer because it lacks complex sugar.
When mash needs to be rested for 60 to 90 minutes at the temperatures indicated for saccharification to occur, the malt is slack.
A spec sheet comes with each bag of malt and near the bottom of the sheet is the line that indicates the length of time it takes for saccharification to occur. Extract efficiency, percentage of protein, color, pH, gravity per pound and level of modification are a few items listed on the sheet. The sheet exists because malt is inconsistent. It's used to determine if the malt is good for making ale and lager or if it's good for making whiskey.
Check out the recipes on Weyermann Malt website. I use their Pils floor malt for everything. It's slightly under modified and low in protein. Under modified malt is rich in enzyme content. Low protein malt has more sugar in it.
