I purchased some white milet malt and after a couple of experiments I determined it was not properly malted and could only convert about 75%.
Also I wanted to make a millet Chestnut ale similar to a brown English ale.
The Chestnut chips where given a rest at 122 for 8 hours with Pectin and Amalyse enzyme added,
I Ran 5 lbs of Sweet potato in my food processer to a course grind so it wouldn't create a stuck mash.
I just wanted the Enzymes and was not concerned about extracting the sugars or starch from the potatos.
I put the sweet potatoes in an oven set to 145, inside a turkey bag. for 4 hours
I then meshed my grains using the Chestnut extract at 150, and added the sweet potato mash. Then let it rest for 90 minutes. At this point it passed the Iodine test.
Note: I peeled the sweet potatos and added additional Alpha Amalyse to the mash. Perhaps the soapy flavor comes from the Skins.
Also I did not try to gelatinize the sweet potatoes
Recipe - 4 gallons
6 lbs Millet Malt
1 lb Oat Malt
1/2 lb Sprouted Quinoa (From Whole foods)
The above grains where given a 122 protein rest for 30 min
4 lbs Med Chestnut chips
5 lbs Course Ground Sweet Potatoes
1 tsp alpha amalyse enzyme
All the above where Mashed at 150 for 90 minuites Then passed Starch test
Used RO water (similar to distilled) for the above, PH was 5.4
Sparged with RO water
Steeped 30 min @ 150, with 1 gal. Med hard water, 1 lb Millet Crystal, 1 lb Med Toasted Buckwheat both about 90L, PH 5.6) and added to boil
Did typical 60 min boil with hops added @ 60, 15, 5
Irish Moss @ 15
Pre Boil volume 5 gallons, Final Volume 4 gallons
SRM about 15
The Sweet Potato worked well to complete the starch conversion. I tried a similar recipe w/o sweet potato and ended up with over 2 oz of starch per gallon.
Taste test of wort, malty, earthy, caramel, coffee, smoky with bitter, nutty after taste.
I noted a lot of people here where giving the sweet potatoes a protein rest at 122, not sure why as sweet potatoes are very low in protein, I do not believe this accomplishes anything.