Sweet Potatoes in Primary...

...actually in un-racked secondary. A couple of weeks ago I did a brew with some home malted/toasted/roasted grains and got very poor conversion. I also added "Amylase Formula" to the mash. The boil included sorghum extract and a little molasses, so there were still plenty of fermentables in the wort.
I was still annoyed at the starches that made it into the fermenter, so after the brew I came to this forum in search of enzyme wisdom and read alot about sweet potatoes.
So my next brew will definitely have sweet potatoes in the mash... but I wanted to help my current brew too.
I peeled and cut up 1/2 of a large sweet potato, and cooked it in water from 90F to 125F, to denature the enzyme inhibitor found in sweet potatoes (that happens @ 90F), and hopefully "excite" the b-amylase enzymes. Then I put my cuttings (the size of steak fries) into star-san (just in case) for about five minutes. After that I added them to the fermenter.
Anyone done that before? One of these days I'm going to read every thread here....
I plan to rack in 3 - 5 days, leaving the sweet potatoes behind. Hopefully by then some of those helpful little enzymes will have ventured throughout my beer, terrorizing any starch molecules they find.
When fermentation is complete, I'll do another starch test and post the results here.

I dunno about the starrsan part, but follow through im very interested!

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There seems to be something about root vegetables and fermenting. I'm not smart enough to figure out what it is. But someone else just posted about a beer using carrots. I looked up the book on google and before the carrot recipe it mentioned that since root vegetables were fermentable they thought they'd develop a beer with a carrot. So I'm interested in what you find with the sweet potato.

Most root vegetables are appreciably starchy, so if you can get the starch to break down, you can ferment them. I'd really like to learn more about the finer points of starch conversion of different grains and vegetables...like what their gelatinization temps are, how heat-stable their enzymes are, what their diastatic powers are, etc. I know indigenous cultures used the amylase in human saliva to achieve conversion, while other cultures use an aspergillus mold called koji to saccharify starches for fermentation. I wonder if koji could be applicable in gluten-free beer brewing, or if it would given off-flavors?

So if you successfully broke down the starches in root vegetables, where would the malt flavor come from? I've been fascinated by the sweet potato experiments, though I haven't tried it myself. Theoretically, I'd bake the sweet potatoes, do some sort of mash, achieve conversion, and end up with a base wort of decent OG. From there, I'd like to add some sort of malted/ roasted grain(s), such as quinoa, buckwheat, or millet, to provide the necessary maltiness. Then I'd brew as normal, adding hops, etc.

Yeah, my guess is malt flavor would be lacking in a root-only beer, and all the Brooklyn Homebrew book's GF recipes involve grains and roots. Hmm...time to do some digging on the diastatic power of root veggies....

I'd like to underscore the reason for this experiment was to break down starches already present in the beer, not to get any further starches or sugars or even flavors; specifically for the enzymes available in sweet potatoes.
DirtbagHB - I'm paranoid about sanitation - even those those potatoes were peeled, cut up and washed, 125F is not enough to kill any bacteria that may have been on them. Since star-san is an acid-based, food-safe sanitizer I'm fairly certain it would do little to any present enzymes.
ChasidicCalvinist - That something about root vegetables and fermenting, for me anyway, is the enzymes. I know sweet potatoes are unusually high in b-amylase, I'm not sure about carrots or other roots.
igliashon & mloster - I was drawn to the sweet potato when I discovered the Amylase Formula I added to the mash was massively insufficient. I plan to use them in my GF recipes going forward to help with conversions... I figure there's plenty of starch and more "beer like" options available for flavor and fermentables, but b-amylase is downright scarce in the GF world. Mloster - along those lines, if you did this: I'd bake the sweet potatoes, do some sort of mash, achieve conversion... You would denature those enzymes prior to mashing (149F beta and 168F alpha) so I would recommend not baking them. I have to find out more about gelatinization but I know it involves "extracting" the enzymes first...
Here's some threads that have helped me, regarding using sweet potatoes):
https://www.homebrewtalk.com/f164/sweet-potato-mash-experiment-211386/
https://www.homebrewtalk.com/f164/sweet-potatoes-amylase-enzymes-lot-interesting-possibilites-210086/
https://www.homebrewtalk.com/f164/gluten-free-recipe-207797/ (specifically the recipe from DKershner and his subsequent replies)

I ended up leaving the potatoes in the fermenter for only 24 hours. I saw green on the potatoes and thought it was fungus or mold forming and freaked. Turns out, they had sank to the bottom, got the hop residue on them, and then floated gently back to the surface... it was only hop residue from the trub!
Anyway I racked the beer. There was definitely increased airlock activity in that 24 hours, and the gravity reading when I racked was down to 1.012! If I had any brains at all I would have done a gravity reading before the addition
I should also point out another reason this experiment was not completely fair - I did add Amylase Formula to my cooled wort prior to draining into the fermenter. However, since it seemed to have done nothing during many chances in a very long mash, I had little hopes of it doing anything on the flip-side either. (I did post a small account of my disappointment in that on day one of that mash)
I should be bottling in a few days, I'll do a starch test and post the results then.

I bottled this last night: FG was down to 1.010 (.0003 below estimated) and there was no starch in the beer. Those things are good, but based on increased understanding of some key brewing precepts, I must declare this experiment totally worthless. Here’s why:

1) I did not test for starch immediately prior to adding the sweet potatoes to the fermenter – bonehead! It could have been gone already! At the time I did not deem this likely (now I do, for reasons I’ll explain), but even so, it should have been done for a starting metric.

2) While I have been concentrating and studying enzymatic activity and availability, I have been neglecting the other side of the process: having starch molecules that are enabled and ready for hydrolysis; gelatinization. My mash had buckwheat and amaranth, which requires min 158F to gelatinize. Since my mash did not venture above that mark on the thermometer, I could have had the most enzyme-rich mash in the world, and those starches would have resisted conversion. Instead of understanding that, I blamed my “Amylase Formula” and counted it as insufficient. This did not prevent me from adding a ¼ tsp of it to my cooled wort, just-in-case… Well, at that point, and remaining starches had definitely been gelatinized during a 1-hour boil. Most likely, the newly-added enzymes went to work at that point, and converted the remaining starches before I engaged in my brilliant sweet potato idea.

Thanks for bearing with me. The good news is the initial pre-conditioned taste of the batch was quite favorable. I’ll post the recipe soon.

MariposaSouth said:

Thanks for bearing with me. The good news is the initial pre-conditioned taste of the batch was quite favorable. I’ll post the recipe soon.

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No, thank you! Going through this experiment with you has been very interesting and educational. Thank you for posting all your ideas and processes.

Just a side note from a post a week or two ago. I've tried sorghum and koji-kin as if innoculating rice once so far. I dumped the result. I may have let it go too far though. I'd consider innoculating rice and fermenting the sorghum as the "rice" additions.

Several pdfs relate to enzymes in different sweet potato varieties, as mentioned, so stick with those.

I question the process of malting gf grains, soaking them in potato enzyme rich water and attempting a caramel malt. (This is on my sorghum malt tests scheduled to begin soon.)

I'm curious why so much attention is being paid to the enzymes in sweet potatoes, bananas, etc. Is there any difference between the enzymes found in traditional grains and the store bought amylase powder? I'm finding the discussion informative and very interesting, but I'm obviously coming from a position of ignorance. Would putting in the appropriate amount of enzyme powder with GF ingredients be the same as brewing with traditional grains?

Hey noontime, thanks for the nice comment (#10)
For the why question, the "amylase formula" I buy at my LHBS is quite mysterious... I can't find anything official about the technical makeup of the formula. I've read from multiple other sources though that it contains alpha and gamma, but no beta. Another potential shortcoming is that limited instructions only mention use in fermentation, not mashing. Whitelabs make an enzyme product called optiMash, for mashing, but it looks like its only available to commercial brewers.
So the goal is to make the mash more like a traditional barley mash, with both alpha and beta; and if we can do it naturally w/o adding a powder, that would be even more cool
KevinM - which "post a week or two ago" are you referring to? I'll watch for your crystal-sorghum malt tests... Sounds very interesting. I've found good instructions in the past for crystallizing barley malt, I'll see if I can find it again and post the link...

It was a post asking about using Koji. I'd have to dig through the last page when I have time.

While I've seen reports of alpha/beta amylase amounts of sorghum, I don't know the quantity listed in other GF grains. They can malt, but the result isn't great. (incomplete conversion). However, some varieties of sweet potatoes and yams can increase this sugar by 6x because of the amount of beta amylase in the variety. And the powder tends to be fungi based and generally alpha.

Yeah, the problem I have about crystallizing malt is which enzymes are involved. (generally pale barley malt that only has been dried/kilned is soaked then heated to have the enzymes make sugar and the heat caramelizes this). If I don't need the extra beta, then I might be able to do that portion without the sweet potato, but I'll be testing that then posting all my tests. I'm writing all the variables of the test now. I still expect the use of the sweet potato during the multi-decoction mash.

I agree with you, i have also the same problem which you have..!