Mashing Sweet Potatoes

[thanantos]

Sorry for all the n00b questions here guys, but from what I read it seems a lot of you are experienced brewers who tend to skip over some instructions that leave some of us behind.

I have been reading about using sweet potatoes and/or bananas in gluten free brews which I understand adds necessary enzymes as well as fermentables?

As I have NO experience with all grain brewing and no fancy equipment, I figured this would be a good guide:
https://www.homebrewtalk.com/f39/easy-partial-mash-brewing-pics-75231/

What I hoped to do is outline the process and maybe you guys can tell me where I will fall down.

My two major sources for this info are the 1920's paper on sweet potatoes:
http://www.jbc.org/content/44/1/19.full.pdf
and igliashon's post here:
https://www.homebrewtalk.com/f164/experimenting-bananas-sweet-potatoes-316232/

#1. Heat 1 gallon (?) of water to 91 degress with a grain bag inside.
#2. Take grated or chopped up sweet potatoes and bananas (along with an optional amount of pre-soaked rice hulls to add in draining) and throw them in the grain bag (in the water) and cook for 1 hour.
#3. Increase temp to 122 and heat for another 1 hour.
#4. Increase temp to 152 and heat an additional 1 hour.
#5. Heat 1.5 gallons of water to 170 in another pot for sparge (rinsing).
#6. Dip the grain bag containing now softened sweet potatoes, bananas and rice hulls in the sparge water to rinse the remaining enzymes/fermentables away.
#7. Hold the grain bag up and let the water drain from it into the sparge.
#8. Throw away the contents of the grain bag.
#9. Combine original water and sparge water to make up your wort water that you will now boil.


Sound right?

Still some questions remain:
#1. Do you mash the sweet potatoes at some point as suggested in the 1920's paper or do you just grate them (peel and all) and call it good?
#2. Do we know how much fermentables or what kind of gravity we expect to get from this combo?
#3. Should the potatoes be cooked ahead of time? I read this thread where it was mentioned, but a lot of what was said was way over my head.

Thanks guys!

 

[igliashon]

First, I've had no success with getting bananas to convert so far. I may have mashed them at the wrong temperatures or not for long enough, but the wort did not come out any sweeter at the end than when it started.

Second, DON'T COOK THE POTATOES AHEAD OF TIME if you want to use them to convert anything. Low-temperature roast them for a few hours if you want to get only their own sugars. Cooking them destroys/consumes their enzymes.

Your method looks fine (grate the potatoes, or better yet puree them). What I usually do--and this is a pretty random/arbitrary process--is chop the potatoes, throw 'em through a food processor, then add a bit of water and put them in a blender and turn them into mush (I leave the skins on). Next: I have two brew kettles, both 5 gallon. I add water to the first one at the rate of 1.25 quarts per pound of potatoes/grains, and heat to about 120 degrees. I toss in the potato smoothie and the grain mixture, and this usually drops it to about 90. I let it sit for 30 minutes. Then I bump it up to about 120--heat on high, stir frequently. Another 30 minutes. Then I bump it up to about 155, also heating on high, stirring frequently--note I am not using a grain bag at this stage. I cover the pot, and usually go do something for a few hours. Come back, heat up the rest of my boil water in the other kettle to about 180. In the mash kettle, I turn the heat on low, stirring occasionally, until the wort gets close to boiling. I notice the taste sweetens a little more as it reaches this stage. Then I add the rest of the water from the other brew kettle, stir vigorously to dissolve the rest of the sugars as well as possible.

Then I stretch my grain bag over the now-empty second brew kettle, and add my rice hulls if it seems necessary (sometimes it isn't, if you can believe it!). I pour the mash into the other kettle, then lift the bag out and let it drain. Then, depending on how OCD I'm feeling, I might pour the wort through the mash back into the other kettle again, and maybe a second and third time if I have the time. What would be ideal is if I had a way to suspend the grain bag over the kettle and pour the wort through it, as the grain bed will act as a good filter to keep out the trub (which can be excessive). I might try to jerry-rig something for that soon.

However, I haven't done a recipe where this is the sole source of fermentables yet, so I don't really know what sort of gravity (etc.) to expect. I will do this soon, though. I'm getting sick of using extracts. I can tell you that so far I've used at most 2 lbs of sweet potatoes in a 3-gallon batch along with 2 lbs of homemade crystal-malt quinoa, and doing a little math via Beer Calculus (taking my final gravity and subtracting the contributions of the extracts, and then playing with mash efficiency settings), I seem to be getting something like 55% efficiency based on the stock PPG values for sweet potatoes and quinoa. I'm going to be a lot more systematic about this in the future.

If you wanted to do a recipe where sweet potatoes and malted grains were the only sources of fermentables, I'd say you'd probably want to use a lot. Expect low efficiency. Mash for a long time, maybe even over night if you can stand it. For a 3 gallon batch I'd probably use at least 5 lbs of sweet potatoes and 5 lbs of some malted or sprouted grain.

What the heck, maybe I'll do just that for my next batch!

 

[KevinM]

Agreed, grate/puree then toss in. If you want to get dry weight, you can grate & dehydrate & crush.
Flavorwise, I'm not sure if there's a difference between the different sweet potatoes. There's usually two or three found in the markets.

I know I killed my enzymes off a bit in my last batch by accident. 2 pounds sweet potato, 2 pounds unmalted sorghum (the early failure). 1 gallon of wort gravity @ 1.10, reduced it down to about half a gallon, though I forgot to measure after.

I was going to drink it yesterday (gravity 1.00, force carbed) and start another batch, this time with malted sorghum but I wasn't feeling well.

 

[thanantos]

First, I've had no success with getting bananas to convert so far. I may have mashed them at the wrong temperatures or not for long enough, but the wort did not come out any sweeter at the end than when it started.

Second, DON'T COOK THE POTATOES AHEAD OF TIME if you want to use them to convert anything. Low-temperature roast them for a few hours if you want to get only their own sugars. Cooking them destroys/consumes their enzymes.

Your method looks fine (grate the potatoes, or better yet puree them). What I usually do--and this is a pretty random/arbitrary process--is chop the potatoes, throw 'em through a food processor, then add a bit of water and put them in a blender and turn them into mush (I leave the skins on). Next: I have two brew kettles, both 5 gallon. I add water to the first one at the rate of 1.25 quarts per pound of potatoes/grains, and heat to about 120 degrees. I toss in the potato smoothie and the grain mixture, and this usually drops it to about 90. I let it sit for 30 minutes. Then I bump it up to about 120--heat on high, stir frequently. Another 30 minutes. Then I bump it up to about 155, also heating on high, stirring frequently--note I am not using a grain bag at this stage. I cover the pot, and usually go do something for a few hours. Come back, heat up the rest of my boil water in the other kettle to about 180. In the mash kettle, I turn the heat on low, stirring occasionally, until the wort gets close to boiling. I notice the taste sweetens a little more as it reaches this stage. Then I add the rest of the water from the other brew kettle, stir vigorously to dissolve the rest of the sugars as well as possible.

Then I stretch my grain bag over the now-empty second brew kettle, and add my rice hulls if it seems necessary (sometimes it isn't, if you can believe it!). I pour the mash into the other kettle, then lift the bag out and let it drain. Then, depending on how OCD I'm feeling, I might pour the wort through the mash back into the other kettle again, and maybe a second and third time if I have the time. What would be ideal is if I had a way to suspend the grain bag over the kettle and pour the wort through it, as the grain bed will act as a good filter to keep out the trub (which can be excessive). I might try to jerry-rig something for that soon.

BIG THANKS MY FRIEND

This is exactly what I was looking for. Nicely done.

AND, I do intend to still use mostly extract, but wanted to start adding sweet potatoes to my batches in order to, hopefully, reduce the amount of Sorghum (because of the twang) and/or other fermentables as they are pretty expensive ($6 a pound or so).

 

[richbrew99]

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