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Old 12-06-2010, 04:55 AM   #1
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Default Sweet Potatoes, Amylase Enzymes, and a Lot of Interesting Possibilites

So I was looking into using sweet potatoes in a beer and stumbled upon some interesting information. Apparently sweet potatoes have enough diastatic power to convert themselves without using barley. And not only do they have diastatic power, but it's mainly from Beta-amylase.

www.jbc.org/content/44/1/19.full.pdf

Here is paper from the 1920's explaining how to go about making a sweet potato syrup, and it's pretty simple. All you do is basically steep them in water at a certain temperature like you would any other beer, then boil them, mash the potatoes, and separate the liquid from the solids.

I'm pretty sure people on this forum have tried this but I don't know how it has turned out, and I don't know if anyone has tried to ferment ONLY sweet potatoes. From what I have read they don't have any free amino nitrogen (FAN) which the yeast need. I don't know if yeast nutrient would take care of this or not, but it's definitely worth doing a one gallon experiment.

People seem to also be of the opinion that the sweet potato flavor doesn't come through very much in the final product.

Well, this sweet potato syrup interested me so I did some searching on the internet and came across an interesting paper.

http://www.springerlink.com/content/np27t162n2184n15/fulltext.pdf

This is not a very fun read but it's only 3 pages and it's got some interesting information. Some people did a study on the diastatic power of sweet potatoes, particularly in use with sorghum to increase yield for brewing. It turns out that sweet potatoes have a lot of Beta-amylase, which sorghum is lacking. They made the sweet potatoes into a flour, and added it in varying weight percentages to malted sorghum, and saw a good increase in yield, with a 4 fold increase in maltose.

Now this got me thinking. I probably wouldn't go to the trouble to make a flour, but I bet you finely grate sweet potatoes and throw them in with any grain/starch of your choosing and convert it into something fermentable and make beer out of it. And then you could throw in some Alpha-amylase enzyme that's cheap and readily available at homebrew stores. Maybe do a little math and crunch some numbers to figure out the right amount to use and you've got a mash with a similar diastatic activity to barley. With that mix you could have a lot of control over the profile of the finished beer, how fermentable it is, and how much body it will have by choosing your mash temperature.

Or maybe I'm wrong. But I know I'm going to be doing some experiments in the near future.

However, there are a few difficulties I foresee with this. One is the low amount of FAN, but I'm hoping some yeast nutrient, high pitching rate, and good oxygenation will make the yeast happy enough. The other problem has to do with the consistency of the sweet potatoes. To make the syrup, they had whole sweet potatoes in water converting their own starches, then they boiled to make the potatoes soft so they could mash them, rinse, and strain. Doing it this way, though, you can't use the sweet potato enzymes to convert anything else. The other guys made a flour which I'm guessing will allow the enzymes to be soluble in water and make the potatoes cook really quick. I'm wondering how finely I would have to chop the sweet potatoes so that enough of the enzymes would be able to dissolve into the water for the mash. I'm thinking I might just pulverize them in a food processor or blender with some water.

Any thoughts?

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Old 12-06-2010, 05:29 AM   #2
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Interesting! They made flour? Do you think they mashed the potatoes and dried them to make potato flakes like instant?

Like you the enzyme thing is interesting. I know in the 50's my parents made potato beer and I can remember the bottles exploding under the house as summer (100 deg heat) approached.

This is a thread I will follow closely! Let us know how it goes shredding the sweet potatoes!

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Old 12-06-2010, 05:42 AM   #3
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It says they kilned them for 24 hours at 55 degrees C (131 F) and then ground them into a flour. I think if they were heated much higher than this like potato flakes probably have been the enzymes would become denatured.

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Old 12-06-2010, 12:45 PM   #4
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The 2nd paper used peeled, sliced, dried sweet potatoes that were kilned and ground into flour. The older paper (1920) used whole sweet potatoes cut into chunks, and a mash at 60 C gradually ramping up to 80C over an hour, then up to boiling after that.

The Gore (1920) paper got a yield of 714 grams of syrup at 37.6 Brix (1.167 SG) after the 1/2 hour boil from 1 KG of sweet potatoes (don't know the amount of water they started with).

There are other publications http://pubs.acs.org/doi/abs/10.1021/jf00022a010 that show the beta amylase is everywhere in the potato and that alpha amylase is only in the skin/just under the skin in the sweet potato.

I'm hoping to do a test batch this week---grate whole washed sweet potato into water, bring it up to 60 C (140 F) for an hour then slowly ramp to 80 C for 30 min, then bring to a boil and see what I get.

tim

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Old 12-07-2010, 12:12 AM   #5
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Very interesting. Subscribed.

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Old 12-07-2010, 12:15 AM   #6
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Yeah I think I will do a one gallon experiment pretty soon too. I doubt that I will get anywhere near the efficiency that they got in the 1920 paper because they used vacuum suction and filter paper. I'm thinking I'll just pulverize some sweet potatoes in my food processor, add water at a 1.25 qt/lb ratio similar to all grain brewing and do the temperatures you mentioned. I think to separate the liquid from the solids I will put everything in a very fine mesh hop bag that I have, rinse several times with hot (170 degree) water and press everything I can out of it.

I can't decide if I want to add alpha amylase enzyme for this experiment or only use the natural sweet potato enzymes to see how it turns out. And then I think I will add a small amount of bittering hops (~20 IBUs) and no flavor or aroma hops to see what kind of a flavor comes through. Probably use Safale US-05 to ferment, and add some yeast nutrient to the boil.

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Old 12-07-2010, 03:32 AM   #7
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Sounds interesting. It makes sense at least, that there is a sugary residue from sweet potatoes on it's own, either roasting or simmering in a little bit of liquid. I've always liked them slow roasted in foil and it always leaves a dark sugary syrup behind that I always liked.

Let us know how the mashed sweet potato tastes after the process and if there's any flavor and sweetness after the rinse. Maybe with some butter and cinnamon sugar.

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Old 12-07-2010, 05:21 PM   #8
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OK i read that 1920's article and decided to give it a try:
I Grated around 4 lb of sweet potato with the skin on, added perhaps 2 liter of water and mashed @ around 70°C for 90 minutes, then brought to a boil for another 30 minutes. I strained, rinsed, and squeezed all the juice out of the potatoes, boiled and reduced the liquid to about 1 liter, it turned out to fairly sweet and a orange hazy color with a disappointing 15 SG. I added the mix to 4 gallon partial mash batch of pale ale (similar to EdWorts). Resulting beer was super-tasti but has slight but almost unnoticeable sweet potato taste. Could just be my imagination.
The leftover potato was definitely less sweet/flavorful, but still quite starchy made a mighty fine sweet-potato bread.

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Old 12-07-2010, 05:49 PM   #9
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Quote:
Originally Posted by hikertrash View Post
OK i read that 1920's article and decided to give it a try:
I Grated around 4 lb of sweet potato with the skin on, added perhaps 2 liter of water and mashed @ around 70°C for 90 minutes, then brought to a boil for another 30 minutes. I strained, rinsed, and squeezed all the juice out of the potatoes, boiled and reduced the liquid to about 1 liter, it turned out to fairly sweet and a orange hazy color with a disappointing 15 SG. I added the mix to 4 gallon partial mash batch of pale ale (similar to EdWorts). Resulting beer was super-tasti but has slight but almost unnoticeable sweet potato taste. Could just be my imagination.
The leftover potato was definitely less sweet/flavorful, but still quite starchy made a mighty fine sweet-potato bread.
Correct me if I am wrong, but shouldn't you have decanted off the liquid from the 90 minute mash before you boiled it? I would think you would want to do this to keep the enzymes from denaturing...
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Old 12-08-2010, 11:10 AM   #10
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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.

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