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Home Brew Forums > Home Brewing Beer > Gluten Free Brewing > Sweet Potatoes, Amylase Enzymes, and a Lot of Interesting Possibilites

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Old 12-08-2010, 03:41 PM   #11
DKershner
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Originally Posted by hikertrash View Post
Ya, I figured that after 90 minutes the enzymes had done their thing and then i was just boiling to soften up the potato to get the sugars free.
I am thinking the conversion was probably not complete. You were mashing extremely thick for how mashes go, which tends to slow things down a lot. I calculate that you should've been using at least 5qts or water...or like 4.75L.

Other than that, your boiling idea was sound enough if the potatoes werent soft enough to mash (like mashed potatoes) from the mash (like beer mash) temps.
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Old 12-18-2010, 01:53 AM   #12
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So I tried this tonight and didn't have very good results.

I looked back at the 1920s paper, and they used one kilogram (2.2 lbs) of sweet potatoes and ended up with 714 grams of syrup at 37.6 Brix (1.167 in Specific Gravity). 714 grams / 1.167 g/mL = 612 mL or 0.162 gallons. So if 1 kilogram of sweet potatoes in 0.162 gallons yields 1.167 SG, it should yield 1.027 SG in 1 gallon of water. Divide that by 2.2 lbs and you get a potential of 1.0123 SG per pound of sweet potatoes. I assumed this was 100% efficiency and assumed I would get around 50-60% efficiency so I bought 6 lbs of sweet potatoes for a 1 gallon batch hoping for a specific gravity near 1.040.

First, I washed the potatoes, then grated them skin on in my food processor. After this I added a little water and turned the food processor on for about 20 seconds to basically pulverize them. After this, I added enough water to bring the total water added to 8 quarts (1.33 quarts per pound of potato) and mashed at 145 for 90 minutes. I added 1/2 tsp of pH 5.2 buffer to the mash, because I remember reading that the enzymes work better at this pH. The mash looked really thin and soupy compared to a normal all grain mash, I think this is because the barley will usually soak up quite a bit of water, but the sweet potatoes have a much higher water content. I strained the potatoes out with a grain bag, and squeezed it to get most of the juice out. I didn't sparge because I already had 2 gallons of wort, the sweet potatoes didn't seem to absorb any water at all. I took a specific gravity reading and it was 1.010, and should have been 1.020 if I boiled down to one gallon. I tasted the wort and it was only very slightly sweet and tasted kind of starchy, so I decided I didn't want to waste hops and yeast on this and I dumped it down the drain. The wort was a cloudy light orange, and a layer of white had dropped down to the bottom. When I tasted this second layer it had a very plain, very starchy taste to it. I don't think I really got any conversion at all. The sweet potatoes strained out very easily with the grain bag, and they were still crunchy and tasted more or less like uncooked potatoes.

I decided not to use the method described in the 1920 paper of boiling and mashing the potatoes after holding at a lower temperature, because my main goal in this was to be able to use sweet potatoes and their enzymes to make beer with other ingredients like other grains or fruits or whatever, in the usual manner that I brew. A lot of things will tend to contribute off flavors if you boil them for an hour and I think it would make separating the wort from the vegetables/grains much more difficult.

I bought enough potatoes for 2 experiments, and I consider this one a failure. I think next time I will use a water/potato ratio of around 0.7 quarts per pound, half of what I used this time. I think next time I will also go ahead an boil the sweet potatoes and mash them to see if I get better extraction this way. I guess if I was making a beer with sweet potatoes and some other grain I did not want to boil, I could do the mash like normal, and put the grains I do not want to boil in a grain bag, and simply take it out before I boil the sweet potatoes. It seems like that would make for a pretty long brew day though.

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Old 01-03-2011, 03:42 PM   #13
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Could it be that not all the starches gelatinized at those temps? I don't really understand this paper, but it sounds like maybe sweet potatoes needs to be hotter for their starches to gelatinize (see Fg. 3 on page 4).
Does anyone understand this better?
I was thinking of using sweet potatoes just as a source of beta amylase -- maybe 80/20 with something like quinoa, that way it's ok if you don't extract much sugar from the actual potatoes.

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Old 01-03-2011, 04:54 PM   #14
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I tried this a few weeks ago: http://www.homebrewtalk.com/f164/sweet-potato-mash-experiment-211386/.

Its carbing in a 2 liter bottle right now. Smelled vaguely like sweet potato when I racked to the 2 liter bottle.

OG was 1.030, fg 1.012 (2.34 % abv).

Someone suggested draining off most of the liquid, boiling the sweat potato to fully gelatinize the starch, and adding back the liquid (after cooling)

Kind of like a large decoction mash

I'll post an update later this week when I try it.

t

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Old 01-03-2011, 05:00 PM   #15
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Quote:
Originally Posted by bonsai4tim View Post
I tried this a few weeks ago: http://www.homebrewtalk.com/f164/sweet-potato-mash-experiment-211386/.

Its carbing in a 2 liter bottle right now. Smelled vaguely like sweet potato when I racked to the 2 liter bottle.

OG was 1.030, fg 1.012 (2.34 % abv).

Someone suggested draining off most of the liquid, boiling the sweat potato to fully gelatinize the starch, and adding back the liquid (after cooling)

Kind of like a large decoction mash

I'll post an update later this week when I try it.

t
Sounds delicious. A friend recently tried just tossing a can of mashed sweet potatoes into a growler with some water and yeast and made something that smelled good, if not technically drinkable.
Did you try an iodine test before fermenting? You obviously had some sugars but curious how much converted.
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Old 01-08-2011, 12:48 PM   #16
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This a glass of the brew I did (see above posts) after 3 weeks bottle conditioning.

ended up 2.6% abv.

Taste: Initially very light, refreshing, fizzy, with pleasant hops notes. Very very faint sweet potato aroma, couldn't really taste it.

Ended with a very strange slippery/oily feeling that left an off flavor in my mouth. Couldn't drink the entire glass because of that.

Its a little hazy, I suspect it is starch haze. The large amount of trub in the fermenter looked like starch particles.

I suspect the slippery mouth feel is from the starch, not sure where the off flavor was from--I realize now that I didn't use a a camden tab to remove the chloramine from the water, and that may be where the off flavor is from.

Not sure I will attempt this again (with sweet potato only) but would add it to a very light beer recipe for the flavor (after fully cooking the sweet potato so the starch is fully gelatinized)

t
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Old 03-03-2011, 03:52 PM   #17
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Default Source of amylase

I read a gluten free mash process, using home malted millet and other gluten free grains, that went like this:
- mash like normal, using a protein rest around 122F and then up to the 150s
- decant off the liquid part of the mash before going to a higher temp, and put the liquid it in the fridge; this is to preserve the enzymes, which would denature at higher temps
- boil the rest of the mash to gelatinize the starch in the partially modified millet malt to access more starches
- bring the mash back down to the 150s, and then add the enzymes back into the mash to finish conversion, there now being more starches accessible to the enzymes because the grain has been cooked

I wonder if sweet potatoes have another potential, rather than as a major starch component of the beer, as a separate source of enzymes.
Could you:
- start with unmalted gluten free grains, cook them at near boiling
- do a small separate mash of sweet potatoes, bring it to around 150F and decant off the liquid
- cool down the grain mash, and add the enzyme liquid from the sweet potatoes to help convert the cooked grain
- the potatoes could then be cooked and added into the mash, or just composted, or made into sweet potato curry (mmm...)

Maybe there is potential here to do a mash with little to no malted grain...I guess we'll have to try it and see what we get.

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