Dextrin Starch Detection

[xetap]

The current laws have made iodine availability harder. I found that Betadine still works the same for detecting starch- it turns a deep, dark purple. The presence of starch is an indication that the corn starch hasn't converted to dextrin, for those few who might not know.

 

It's still available OTC- as is iodine- if you can find it and then you have to sign for it after asking the pharmacist to get it for you. Many places have stopped stocking it due to the hassle.

 

The attached image shows the reaction. The right shows a batch that was baked for 3-1/2 hours at 375 degrees F- and still isn't done.

 

The batch on the left was baked for <2 hours, at 425 degrees F. It's done. YMMV.

 

Edit- Switched image descriptions- thanks Tentacles.

 

Edited January 16, 2009 by xetap

[tentacles]

Another option is iodophor sanitizer - good homebrew shops should stock it. Are you sure your picture isn't switched around? The sample on the right is dark enough to appear black, the one on the left is merely reddish with some darker patches.

 

Also the gelatinous/viscous look of the sample on the left looks like the dextrin dissolved.

 

There was some recent discussion on passfire about baked dextrin being inferior to acid modified (then baked) dextrin. The idea was that the commercial baked dextrin is done in a calcining oven, which is sealed to keep oxygen out, so baking it in an open-air oven (and stirring it, god forbid) prodcues an inferior product. My thoughts were that the calcined stuff is processed at a temperature high enough to actually burn/set fire to the starch. The stuff I baked certainly appears and works like what I bought from firefox.

Edited January 15, 2009 by tentacles

[tentacles]

On a side note, I found that cooking mine at 425F was much more effective than at 375 as well. I wouldn't recommend going higher than 425 though, or it might start burning.

[Aimlesspayload]

On a side note, I found that cooking mine at 425F was much more effective than at 375 as well. I wouldn't recommend going higher than 425 though, or it might start burning.

 

I made dextrin a few weeks ago. It was my first time, and I made way more than I should have tried to. I've been using it in TT stars and it seems to hold it together fine. The thing is, I diluted some "dextrin" in water a few days ago, then added the iodine and it was very purple. I dunno, seems to be working fine so I wont be replacing it. Has anyone used just regular corn starch as a binder? (I don't know if it will even act as one...)

[Swede]

+1 on the >400 degrees note. It does work better. I'm tempted to try a batch sealed in some sort of retort, covered with nitrogen, in my shop oven. I also noticed that it seemed to take FAR longer to convert than the books might indicate. Plus, the smell, that funky, burnt corn-starch smell.

 

My commercial dextrin does not have this smell. Can we replicate the acid-catalyzed conversion process at home?

 

Xetap - Really cool tip on the iodine - something simple, yet effective. Thank you.

Edited January 18, 2009 by Swede

[tentacles]

Swede, I'm sure we can, but it's an awful lot of trouble to wet the corn starch in a slightly acid solution, then dry it, break up the clumps, and then bake it (albeit at a considerably lower temperature).

[Mumbles]

There are some patents out there for the inclusion of boric acid to the corn starch. I believe industrially they pass gaseous HCl over the stuff. I thought it was while it was cooking, but I'm not sure. The acid stuff is supremely sticky and dries really hard though.

[Richtee]

Corn starch has no real binder/adhesive quality when uncooked, BTW.

I suppose a paste could be made and then brought to simmer temps and added. But what a mess. "Red Star Gravy" or some such ;{)

[Richtee]

Swede, I'm sure we can, but it's an awful lot of trouble to wet the corn starch in a slightly acid solution, then dry it, break up the clumps, and then bake it (albeit at a considerably lower temperature).

 

When wet with water, the starch dries to it's powdered form again fairly well. It does "compact" some, but would break up quite easily. Dunno about with an acid tho. What is the acid supposed to do? Comtribute to the protiens linking?

[Mumbles]

It's the carbohydrates that we want. They start as long chain carbohydrates. The heat breaks them down into smaller units. The smaller the unit, the stickier it is. Anyone who makes beer knows this. The grains are significantly stickier after mashing than before.

 

The acid further hydrolyses the bond, thus shortening the chains even more by hydrolysing the bonds. Again with the beer making, but you make invert sugar by heating the sugar with acid. It convert sucrose into fructose and glucose.

 

http://en.wikipedia.org/wiki/Inverted_sugar_syrup

[Richtee]

It's the carbohydrates that we want. They start as long chain carbohydrates. The heat breaks them down into smaller units. The smaller the unit, the stickier it is. Anyone who makes beer knows this.

I DID know this...just not technically..LOL- especially the acid thing. Seems a dilute acid moistening and a dry period/bake would work then?

[tentacles]

xetap:

 

"'Dextrine is obtained by heating starch [...] in powder form to 200-270 deg C *or* (emphasis added) 0.15-0.3% of nitric acid [...] is added [...] and heated to 100-120 deg C. The former product is called calcinatory dextrine and is brownish; the latter is called acid process dextrine and white or yellowish.''"

 

Not my words.. I believe it's an excerpt from FAST. I think you can use a .4-.5% HCl instead of nitric. The percentages are probably on a per mass basis.. and don't forget to convert for the correct amount of whatever concentration HCl you have - 31-37% for muriatic acid.

[Mumbles]

I cook my dextrin in the household oven. I'd be wary of adding any sort of volatile acid to the dextrin first. This is why I mentioned the patents about the boric acid.

[tentacles]

You'd use a solution of the acid to soak the starch, then dry it, and finally bake the dried acid-modifed product at 100-120C. I would dry it thoroughly outside and then bake it once dry - although in industry, it is probably simply heated in the oven to dry it quickly and bake it. If you've got a toaster oven for science, you could do it outside I suppose. I would NOT bake it inside with a volatile acid added to it - without drying off the acid first.

 

I'm kind of assuming that it's acid modified in solution, but I don't see how you'd add the acid during the baking process, as HNO3 would decompose at 100-120C. Industrially, it may be acid modified "dry" with a vapor process but that's hardly practical for us.

[FrankRizzo]

Here's a good article:

 

http://ljs.academicdirect.org/A07/09_16.htm

 

While it deals specifically with Cassava starch, according to an MIT paper I read the other week, the method is completely applicable for maize (corn) or potato starches as well.

 

The best yellow dextrin was achieved with an acid (HCl) concentration of 0.3M, roasted for 180mins at 90°C. The starch is in fact processed damp with acid (if dry, the acid would be gone).

[Mumbles]

Just because it's not starch, doesn't necessarily make it soluble. I generally rely on color, cook time, and yes taste to determine when the dextrin is done. I don't have to use the iodine, though I have before just to confirm. When it's done, to me at least, it takes on a light to medium tan color. No batch is ever the same, but it's always fully converted. It also gets a slightly sweet taste to it, and feels more slippery.

 

With the acid converted stuff you can easily tell. If you wet your fingers and get some dextrin on them, rub them between your fingers a bit and pull them apart. There are strings.

[Swede]

The acid conversion has me intrigued now. How about putting your HCl in a spray bottle, then, working outside, with a big bowl, mixing spoon, and acid, spray the surface of the starch. Work it in with the spoon, spray again, etc, until the mixture is damp. Then, spread it out on a sacrificial cookie sheet and bake at 90C.

 

But how to process the dextrin? Will it simply dry out during the roasting process?

[FrankRizzo]

Right. The acids mentioned for use (HCl and HNO3) are both solutions of gases in water. If the water is removed, the gas comes out of solution. For this reason, it's not wise to use your kitchen oven for this experiment...you'll likely rust any exposed metal that isn't stainless (i.e. the door hinges, screws, etc.). Having the acid in the air you're going to be breathing is also a very bad idea.

[FrankRizzo]

Hear hear Xetap! ...if only I had a bigger garage (and house)

[Swede]

I apologize for resurrecting this old thread.

 

I have yet to try acid-based dextrin, but I DID try something different... I loaded a stainless steel container about 1 liter in size with corn starch, and began to bake that at 420 degrees F. Interestingly, after several hours at temp, those portions of the starch exposed to oxygen (and possibly slight ambient humidity) had turned to the standard tan color, but at the core of the container, it was snow white. I should have saved some of the snow-white stuff to test it and see if it had converted, but my thought at the time was that it was still raw, so I simply stirred it around and let it cook until the whole batch was tan.

 

The question now is, what is the effect of spreading it out vs cooking it as a mass? Is exposure to air necessary for the conversion when not using acid? Or is the tan coloration simply an unwanted byproduct, oxidation of some sort?

 

I still want to try the acid method. The boric might be a way to keep the whole thing dry, and less messy. I'll give it a shot today if I can find some raw starch... I might be out.

[Pretty green flame]

I still want to try the acid method. The boric might be a way to keep the whole thing dry, and less messy. I'll give it a shot today if I can find some raw starch... I might be out.

 

Why not cook some starch in diluted HCl, it was a fun experiment we did, you can actually test it with Iodine to determine when all (most of it anyway) the starch has been converted into dextrine. Though overcooking will give you glucose which is bad. I think it has to be in solution for the acid to work, could be wrong though.

 

I have a question though, what kind of transformation does starch go though if it is heated in an alkaline enviorment (diluted NaOH for example)? It does change colour to a pale yellowish state and becomes somewhat transparent.

[FrankRizzo]

Swede, the reason the center didn't get cooked is because of the insulating effect of the outer material. It's similar to how you get a nice crust on bread, but the inside remains nice and moist.

[Swede]

Swede, the reason the center didn't get cooked is because of the insulating effect of the outer material. It's similar to how you get a nice crust on bread, but the inside remains nice and moist.

 

That is what I thought initially, Frank, but the container had been soaking at heat for at least 5 hours. I would have thought the temperature at the core HAD to be stabilized by then. That is why I was looking to other variables, as you mentioned, moisture, oxygen (or lack of it), anything else. The container was only about 5" diameter by 6" tall or so, nothing huge.

 

Oh well, it's an oddity. Maybe the temp WAS lower at the core. I've got so much dextrin now, as much as I'd like to mess with an acid method, I may as well use up what I have first. PGF, it's definitely on my "to do" list. Small samples with one variable each, see what works best.

[TigerTail]

I always cook my dextrin on a gas stove on low flame, in a heavy bottomed pan. It takes about 1/2 hour with constant stirring to achieve a colour with iodine solution in between the two in the first post when cooking about 75 grams(that lasts long enough for me ). The end product works fine for making stars.

 

Any comments about this method?

[dagabu]

Nope, looks good to me. I gave up on homemade Dextrine and buy it already processed with acid, it is stickier and more consistent plus, it is the same per pound when bought in 20# lots as is the corn starch from the store.

 

-dag