Ok, here goes on something that I tried on a current working all-grain mash of 50% corn / 50% unmalted white wheat.
I cooked the ground corn and gelatinized it by taking the boil to 200 F and letting it set overnight. In the morning, the temp was at about 130 F. I added a tlb spoon of Alpha Amylase and it instantly fluidized the corn starch to sugar. I then added the ground wheat and let it set for a half hour to gelatinize the wheat starch. I then took the temp up to 152 and held it there for a half hour. I then let it cool naturally and when it was less than 90 F, I mixed it up with my drill and a drywall mud mixer. When well aerated, I added a tlb spoon of Red Star bread machine yeast.
The action took off pretty well as I ferment on the grain and I have to mix the mash down a couple times a day for the first few days. The OG was 1.058. After 3 days, the SG was 1.022 and appeared stuck. Very little activity. The pH was between 4 and 6, looked inbetween on the litmus paper. I don't have a pH pen. So I figured what the heck. I threw in a tlb spoon of Gluco Amylase (GA). Within about 6 hours, I had a half inch of foam on the top of the mash.
I was out of town over the weekend, and checked it tonight. The SG is 0.992. The SG was 0.998 after 8 days and 0.992 after 12 days.
Here's what I figure. The GA does its best work at around pH 5 and room temp. The natural activity of the yeast brings the pH down to about pH 5. By dosing the wort with the GA after 3 days of working, it is likely that I was at optimum for the GA to do its duty. I probably ended up a ABV of about 8.66. It will have to be a few more days before I can run it thru the still. I'll do one last SG before I run it. What do they say about the prood of the pudding?
I don't profess to have any or all of the answers on how or why this process has worked, but it may be someone's answer to stuck mashing. I intend to try this procedure again on my next corn mash and I'll update on what I find. If someone whats to weigh in on what additional sugars were converted to fermentables with the GA, I would appreciate their insight.