Making Dextrin

[TranslucentDragon]

Hey all,

I am making dextrin using the conventional 400 degree Fahrenheit oven cooking a batch of cornstarch on a cookie sheet for two hours, stirring every 15 minutes. I just completed this process about 20 minutes ago, and put a couple drops of iodine/povidone solution in the water filled dixie cups. As I put the drops in the cups, there was a minute amount of blue, precipitate looking material at the bottom of the cup, I figured this was some ink from the cups (as they were colored) or maybe the iodine reacting with the paper. I put about a gram or two of my dextrin mixture into the solution and it turned blackish blue. I realize this means my dextrin still has cornstarch in it so now I'm wondering:

1. Do I need to cook the cornstarch longer, if so do I just use the same method and cook longe or do I need to revert to a different method (see #2).
   
2. Should I use the method where I put it in the oven at 350-360 degrees Fahrenheit on a cookie sheet for 8 hours
   
3. Can I put the already cooked cornstarch that's at least partially dextrin back in the oven even though it has cooled.
   
4. If I need to use the method in #2, should I start with a fresh batch of cornstarch, or can I use the already cooked (at 400 degrees for 2 hours) dextrin/cornstarch mixture.
   

I don't want to buy my own, as I want to learn to make it, so I would appreciate not hearing, "Just buy some dextrin online, its soooooooooo much easier!"

 

It seems to have at least partially converted to dextrin because when I mixed the mixture with water on my hands they became immediately sticky, although I did think that it wasn't a very sticky substance. It felt like it wasn't as sticky as glue, but was stickier than playdoh.

[Bobosan]

400 degrees seems high. If I remember correctly, last time I cooked cornstarch I used 200-250 degrees for approximately 4 hours, stirring occasionally until the entire batch turned to a dark tan to almost brown in color. It's going to stink a bit as it cooks. I use a wide tooth comb to stir the mixture on a cookie sheet.

 

I would use the partially cooked mixture and see if you can complete the cook. Worst case is you start over and make a new batch.

[TranslucentDragon]

I put it in the oven for another 2 hours at 250 and it seems stickier but the iodine keeps turning purple. Actually, when I mixed in the mixture, the iodine turned dark purple, but I kept stirring it, and then it turned back to a brownish orange. The mixture looks golden, slightly darker than beige, making me think it looks ready, and it feels ready when I mix it with water, but since I have no experience with it I really don't know. I don't want to put this stuff in BP if its still just cornstarch. Anything I can do to make sure if it is or isn't ready? Edited September 29, 2013 by TranslucentDragon

[psyco_1322]

I usually just cook it until it turns the golden brown color. It usually takes around 3-4 hours, even though they quote 2 hours. I think it varies greatly with peoples stoves and the container they are cooking it in, just like cooking food.

[Seymour]

I cook is at slightly over 200 deg C. I do it like Psyco, just until it's golden brown, though to be honest, brown is pushing it, more tan. I have cooked it until it's brown brown and it seems stickier, but it is in my experience too close to burning it to be worth it, considering that I have no problems using the nice golden stuff in stars with 4%. They get rock hard.

 

It helps to keep some of the original cornflour at hand to compare the colour to if you are unsure. When you compare the two, even somewhat lightly cooked dextrin is a quite noticeably different.

[nater]

You might be able to make functional dextrin by baking corn starch, but you will not convert all of the starch by baking alone. There is more to the commercial process that I am only vaguely aware of. I know it involves acid, but I don't know more. Take a sample of what you have and add some water to it to make a thin paste. Is it sticky?

 

I did it once in the oven, the results were so-so. I did not think the stink and the burning eyes was worth it. My wife appreciated that even less.

[TranslucentDragon]

You might be able to make functional dextrin by baking corn starch, but you will not convert all of the starch by baking alone. There is more to the commercial process that I am only vaguely aware of. I know it involves acid, but I don't know more. Take a sample of what you have and add some water to it to make a thin paste. Is it sticky?

 

I did it once in the oven, the results were so-so. I did not think the stink and the burning eyes was worth it. My wife appreciated that even less.

 

I never really had an issue with the stink. Personally, it smelt like burnt popcorn and cornstarch so it didn't bother me, wasn't the most pleasant thing but then again, we work with pyrotechnics.

And does that mean no matter how much or long I cook it, it will always turn an iodine solution purple? Because my biggest issue right now is that it feels sticky, and is a golden/tan color, but it won't pass the iodine test, and I don't know any other ways to test it.

[nater]

Yes, like I said, baking alone will not convert all of the cotn starch to dextrin. You can make functional dextrin this way, but not pure.

 

If the solution you made is sticky, just try it out. Make a small batch of granulated BP and pump or cut a few stars too. If they dry hard enough, what you have will work.

 

You are also right that we work with things that smell worse than baking corn starch. Those take place outside and not in the kitchen. When I said my wife didn't appreciate it, that was an understatement. Gotta keep her happy too.

Edited September 29, 2013 by nater

[Mumbles]

No, you will never convert all of the starch. Homemade dextrin will work, but it is truly a half-assed version at best compared to the real deal. It should also be noted that dextrins will react with iodine as well. They turn red, which can be hard to discern from the blue-purple if you have a mixture.

 

I've never really noticed much of a smell. Maybe it was just me, but I never got this eye burning terrible smell that people seem to describe. I cooked at 350F for 2-3hr, and pumped it up to around 400F for the last 20-30 min or so. The best way for me to test how done the cook was, was via taste and texture. When getting done, it starts to taste sweet to me, and loses the starchy, chalky taste of starch. The product itself is both slippery and sticky. It's sorta slippery, and pulls into strands when I pull my fingers apart.