Uh, moonshiners have been converting starches to sugar without mash temps for a long time.
Basic recipe: take a bunch of corn, and bury it in manure. Leave for 10 days, then come back and wash the manure from the corn (its now malted). Dump that with some horse feed (which contains barley) and put it in a big container. Top the container off with water, and dump some bakers yeast in it or a partially baked loaf of bread. return in 1-3 weeks and distill. The yeast will eat up any sugars immediately after they're converted from the starch, and preserve the mash from most infections. ... Supposedly its really inefficient, and to get the full conversion, you have to take the back-set (the stillage after the whiskey is distilled) and dump it back on the mash. Corn and barley, 80%/20%, takes about 3 times before it's fully converted, or so the old lore goes.
I'm actually going to try a sour mash using this method once it warms up here (Pac NW). EDIT: for a beer, minus the manure...
Decomposing manure gets really warm, that's where the mash temps are coming from. Here's another historical possibility! Good post.