I stumbled upon this thread while looking for a potential solution to an entirely different problem - having pressed apple juice that still had starch in it due to pressing unripe apples.
I was looking for a way to convert the starches in the apple juice into sugars without the use of commercial amylase. One potential solution I came up with was to simply incorporate the apple juice into a mash, wherein I hoped the malt's amylase would convert some/all of the starches.
BUT I was worried about Mash pH impacting starch conversion, and thought that in order to reduce the risk of totally stalling the mash, I would do a two-step mash: 1) Mash normally, 2) add apple juice as a 2nd infusion.
Before testing this on a full batch, I decided to do a small test-batch. Here are the photos and the result! NOTE: I used 3/1, malt/wheat for the mash. I am SURE that this impacted my results re: residual starch at the end of the mash. There WAS residual starch at the end of BOTH the pre-and post-apple-juice-addition mash steps. I'm posting this here as an "experiment one" with more to follow!
-Mash-in with 1 cup hot-water-tap water and 3/1, malt/wheat, 1 cup water (topped up to 1.25 cups after 30 mins)
-Heat to temperature in double boiler. Maintain temperature around 150f by adding direct heat.
-After 60 mins, do starch test. Woops! Still starchey. Mash for 30 more mins at 150f.
-Add apple juice and direct-heat until back up to 150f. Maintain for 30 mins.
-"Mash Out" by heating to 170f and straining
-Boil for 15 mins.
Final starch test:
Final product in container:
Notes: Mash temp was not maintained perfectly at 150f. Max temp: 158f. Min temp: 144f. (generally held between 148-154f)
As I said, nothing conclusive here as to whether you can mash with apple juice only (I suspect no due to pH) OR if apple starch can be effectively converted (as I suspect all or some of the starches at the end were from the wheat and not from the apple).
Will follow up with my second experiment!