Sweet Potatoes, Amylase Enzymes, and a Lot of Interesting Possibilites

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JumboBlimpJumbo

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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. :rockin:

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?
 
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!
 
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.
 
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
 
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.
 
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.
 
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.
 
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...
 
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.
 
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.
 
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.
 
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.
 
I tried this a few weeks ago: https://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
 
I tried this a few weeks ago: https://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.
 
sweet_potato_brew.JPG


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
 
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.
 
I'm the oddball here as I don't generally care for alcohol nor carbonated beverages. I enjoy the taste of various juices and when sweet potatoes went on sale this year, I bought a case and juiced them, loved the juice and bought the remaining 9 cases and juiced them.

While I enjoyed the taste of the fresh juice and the feel/taste of the raw starch, I thought it better to allow the starch to settle out overnight and then pour off the juice and add more water to the starch to rinse it cleaner for eventual drying. For at least the last 3 gallons I made, I noticed that the juice (without the majority of the starch) had separated with most of the pigment and maybe very fine fiber settling out leaving a thin liquid looking about the color of apple cider maybe a little lighter. The liquid was not sweet and was slightly carbonated and probably contained some percent of alcohol. The raw starch that settles out likely has plenty of amylase to break it down. The starch that I am adding rinse water to, shaking up, and letting settle ferments even in the refrigerator so if you are deliberately trying to ferment it should be very easy. A Champion juicer will get a decent amount of juice out and is one of the easier to clean up. I found my Angel twin gear juicer gets more juice out and if I run the pulp from a case or two through it a second time, I get about one gallon more juice (including starch and some fiber that gets through). Since most if not all of you here are not trying to get the most juice separated from the pulp, you may even combine the juice and pulp for fermentation. You may also choose to use a less expensive juicer such as the centrifugal juicer. I think they are more of a hassle to clean than the champion and many of them have limited size pulp collection containers. The Champion may be your best choice and you might even put one container to collect both the juice and pulp together. In addition to the amylase in the sweet potatoes, there likely was natural yeast on their skin. I only made sure they appeared clean and cut off any bad spots before juicing.
Attached is a photo of the bubbles in the rinsing/settling starch and you may notice a highly pigmented third layer between the starch and the large liquid layer. This gallon is the starch combined from probably 4 or more gallons of fresh juice
 

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