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bonsai4tim 12-12-2010 11:32 PM

sweet potato mash experiment
This thread http://www.homebrewtalk.com/f164/sweet-potatoes-amylase-enzymes-lot-interesting-possibilites-210086/

lead to more reading. Sweet potatoes have amylase (alpha and beta) in them, and a fair amount of starch. In africa, adding ground sweet potatoes to the sorgum mash significantly improved yields in beer making.

So this afternoons experiment:
2.5 pounds grated sweet potato (including skins)
2 gallons water at 150 F

Mashed for 90 minutes, did a single decoction (see note below)

Ended up with 1 1/2 gallons at sg 1.015

1 hour boil with 1/4 oz fuggles. to 3/4 gal and sg at end of boil 1.030

Will pitch s-05 (its what I have) when it cools. Not sure if this will even be drinkable, but the science is fun!


note: one paper, can't find it now, said the starch in sweet potatoes wasn't fully gelatinized until 180F, which is above the temp that the amylase in sweet potatoes is inactivated. Probably should have done several decoctions to increase the avail. starch for conversion

DKershner 12-14-2010 04:12 PM

1.030 gives you 30% yield. Normal malted grain gives about 75% for comparison. I would suspect this is because of the gelatinization temps you mentioned...not sure how to get around that exactly. Decoction might help a bit, but would also reduce the amount of enzymes.

The temperature quandary is common among GF grains.

bonsai4tim 12-15-2010 09:12 AM

I knew the yield was really low. This was more of a science experiment. Also wondered about cooking 1/2 of the sweet potatoes completely and shredding the other.

A finer shred might help too-

This is fermenting away now, will post an update when its done.


AnOldUR 12-15-2010 09:43 AM

Interested in hearing your results. My wife loves sweet potatos (not a fan myself.) If nothing else, I think she’d like the novelty, but I’m wondering what it’ll add to the flavor if used as part the grain bill.

Did a "sweet potato" search. Lots of information. Thanks for idea.

BBBF 12-15-2010 05:32 PM


Originally Posted by bonsai4tim (Post 2477827)
I knew the yield was really low. This was more of a science experiment. Also wondered about cooking 1/2 of the sweet potatoes completely and shredding the other.

A finer shred might help too-

This is fermenting away now, will post an update when its done.


Soak the potato grated potatoes in the mash for a while, drain out the liquid (it has the enzymes in it), boil the potatoes, add the liquid mash back in, but make sure the combined temperature is where you want (too hot and you'll lose the enzymes) and then perform a mash and lauter like you would for regular beer... And add a lot of rice hulls.

daxdefranco 01-31-2011 11:57 PM

how'd this turn out? i'm thinking of making a sweet potato beer sometime this week.

cuttsjp 02-02-2011 01:09 AM

Sweet potatoes and other potatoes are supposed to be gelatinized (read: cooked) before you add them to the mash, so next time just boil or bake them beforehand and then smash them to a pulp and add them to your mash. I love pumpkin beers and I decided to take that whole thing a little further and do a "sweet potato pie" ale next fall. May not even wait that long...

daxdefranco 02-02-2011 01:15 AM

After I read a little more about this, I found several different research papers that puts the gelatinization point of starch in sweet potatoes between 58-80C. I've got ~3Kg of sweet potatoes baking in my oven at the moment at 150C for 2 Hours. After that I'll shred/mash them and mash at 67C.

imrook 10-04-2011 02:24 AM

I have been doing some homework on brewing with sweet potatoes recently and wanted to post some findings here for potential future visitors.

Sweet potatoes are mostly water and around 22 - 25% starch by weight ( http://www.fao.org/ag/aga/agap/frg/AHPP95/95-217.pdf & http://journeytoforever.org/biofuel_library/ethanol_manual/manual8-10.html )

If sugar is 46 PPG (100% by weight) then sweet potatoes should be 46 * .25 = 11.5 PPG. I know this isn't 100% scientifically correct (so if someone has the real number please chime in) but it should get us in the ballpark.

So in your experiment, 2.5 lbs of sweet potato has a theoretical max of 2.5 * 11.5 = 28.75 points. You got 30 * .75 = 22.5 points. That's an efficiency of 22.5 / 28.75 = 78% which seems about right for a typical all-grain brewer.

cuttsjp is quite correct that potato starches should be gelatinized before mashing to maximize yield. I suspect that a significant fraction of your O.G. is in unconverted dextrins. I know it has been quite some time since the original post. Did you ever take a F.G. reading? If so what was it? How did the resulting beer taste? Starchy? I recently brewed my first sweet potato beer after doing a fair amount of research. It seems strange to me that so little is known about brewing with this vegetable, though it seems to be a great candidate for adding variety to the fermentable list for all-grain brewers. You can follow the progress of my (and others') sweet potato beers here: http://www.homebrewtalk.com/f76/crazy-bettys-sweet-potato-pie-ale-ag-269624/#post3350258

aomagman78 10-20-2011 10:06 PM

imrook - I think your math is off. I'm not sure exactly the stoichiometry of it all, but a single starch molecule will break down to form many sugar molecules. I'm not exactly sure how this calculates into PPG, because 26wt% starch would also mean 26wt% sugar once converted. So maybe you don't need a conversion factor. But now I'm curious myself - I may do a sweet potato mash/decoction and include amylase powder.

Plan: 3lbs sweet potato (food processed) in 1.25gallon water @ 80F. Raise temp to 122F, rest 30 min. Pull 3-4qt heavy mash for decoction (all sweet potato). Boil for 10min, return to mash. Bring mash to 152F, add amylase powder. Rest for 60min - check gravity of cooled sample. Pull 3qt for second decoction. Boil, bring mash to 170F, rest 10 min. Sparge with 1 gallon 170F water. Should have 2 gallons of water, check gravity and boil. I'll ferment this with some US-04 and see how far it'll go.

Thoughts on this schedule?

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