Science Wanted: kitchen powder identification edition

July 21, 2014 11:28 PM

I have a large tupperware full of a crystalline white powder. It could be sugar, or it could be xylitol. How can I tell? So far I've found two possible ways: burn it and record the energy per gram; feed it to dogs. I would prefer not to do the second, as xylitol kills dogs. I'm open to the first, if someone wants to link me to a good experimental method for such. But I'd really love a third way.
posted by freyley to Food & Drink (19 answers total)

Is tasting it out of the question? A teaspoon into a cup of tea, coffee, water?
posted by bleep at 11:39 PM on July 21, 2014 [1 favorite]

Does it melt and caramelize like sugar?
posted by mollymayhem at 11:45 PM on July 21, 2014 [3 favorites]

Best answer: Apparently xylitol is only 75% as water soluble as sucrose. That might be one way to tell them apart - take two jars, put 50ml of water in each. In one put 100g of sugar. In the other put 100g of mystery chemical. Shake them a bunch until they seem pretty good and dissolved. If less mystery chemical dissolved than sugar, it's xylitol.

(reduce the quantities to the smallest amount you can conveniently and consistently measure)
posted by aubilenon at 11:51 PM on July 21, 2014 [1 favorite]

In my experience xylitol crystals are noticeably larger and coarser than sugar crystals. They look quite different to me, even to the naked eye.
posted by Bella Sebastian at 12:07 AM on July 22, 2014

Best answer: Xylitol crystals are coarser than typical North American table sugar crystals. They're also more of a cool white colour versus the creamier white of table sugar, which looks very much like table salt.

The solubility test described above looks safe and easy, but if you have the right equipment on hand, you might try determining the melting point of the stuff. Sugar and xylitol have different melting points:

Sugar: 366.8°F (186°C)
Xylitol: 197.6°F (92°C)
posted by maudlin at 12:23 AM on July 22, 2014 [4 favorites]

Yeah I would go with a melting point test like maudlin recommended.

Assuming access to a kitchen and a known source of sucrose one way to test it would be to say take some Al foil and make two little flat bottomed dishes with it with a slight lip, and place them both on the bottom of a pot or pan....place it on a cold stove top and put a scoop of your unknown powder in one and a equal amount of the know table sugar/sucrose in the other and slowly start to heat up the pan. The xylitol will melt long before the sucrose.
posted by Captain_Science at 2:53 AM on July 22, 2014 [3 favorites]

Best answer: "But I'd really love a third way."

Apparently, based on my twenty minutes hour of late night "research", Xylitol is eschewed by ants. Ants seem to prefer more easily broken down sugars. A sort of backwards low tech way to differentiate your mystery white powder might be to capture some ants and place them in a container with one small pile of each substance and see which one they seem to be prefer.

http://www.alphaecological.com/news/do-ants-prefer-a-specific-type-of-sugar/

http://www.education.com/science-fair/article/ant-behavior-artificial-natural-sugars/

p.s. this is a fun question.
posted by vapidave at 3:26 AM on July 22, 2014 [2 favorites]

Best answer: I would create a super-saturated solution of known-sucrose, a super-saturated solution of known-xylitol, and a super-saturated solution of mystery-chem, and then leave all of them out to dry, and compare the crystals. It looks like sucrose crystals (i.e. "rock candy") don't look anything like what xylitol crystals look like. A small amount of the super-saturated solution in a petrie dish should dry up in a day or so.
posted by Chocolate Pickle at 3:30 AM on July 22, 2014

I was going to suggest weight, but it is ridiculously difficult to google the weight per volume of these substances. Some sources say that 1 teaspoon of sugar is 4.2 grams, but most places round it to 4 grams. Xylitol also looks like it's 4 grams per teaspoon, but I can't tell if that is rounded or not.

You might try to weigh a level teaspoon of known-sugar and one of known-xylitol and compare those to the exact same measure of your unknown substance. Based on the very similar parameters, this experiment has a high risk of being not definitive, but if you have a kitchen scale it is quick and easy and it might work.
posted by CathyG at 5:34 AM on July 22, 2014

Based on the above, one melts in a double boiler, one doesn't. What could be easier.? (The pan containing the mystery chemical may have to touch the boiling water.)

If you put a little sugar in a teaspoon and heat it with a match or candle, it will caramelize in a familiar way. If the mystery chemical does something different, it isn't sugar.
posted by SemiSalt at 5:43 AM on July 22, 2014 [1 favorite]

A small correction: dissolving and recrystalization doesn't require super-saturated solutions. Pretty much any reasonable solution would work. It's easy, it shouldn't take too long, and I think it would be definitive.
posted by Chocolate Pickle at 7:40 AM on July 22, 2014

My solubility suggestion might work, but checking the melting point seems much less fiddly.

The easiest way I can think of to test that is: Put some of it in the oven at 300°F. If it melts it's xylitol, otherwise it's sugar. A metal bowl or measuring cup would be a good container to get it up to temperature quickly.

Also: Let us know what it turned out to be!
posted by aubilenon at 9:36 AM on July 22, 2014

Response by poster: Okay, this is wonderful! Thank you all! I will report back tonight.

I'm leaving some out for the ants right now, and then tonight I will try both solubility and meltability.
posted by freyley at 9:38 AM on July 22, 2014 [2 favorites]

Trying to proof yeast with it might also be interesting.
posted by Bruce H. at 7:10 PM on July 22, 2014 [1 favorite]

Response by poster: - Ants ignored it (by weighing the sample before and after)
- Solubility test was challenging to read.
- In a 300 degree oven it did not melt.

Planning to do the crystallization test tomorrow after I get a new bag of xylitol to compare against, and I'll do the melt test with the control too. I might also try the double boiler too.
posted by freyley at 11:20 PM on July 22, 2014 [2 favorites]

Are you absolutely sure the powder is not something toxic? If you know it is safe to eat, then just taste it. Xylitol has a slightly minty flavor, mixed in with the sweetness. Sucrose does not.
posted by artistic verisimilitude at 4:57 PM on July 23, 2014

Xylitol doesn't caramelize. Put it in a non-stick pan and crank up the heat. Does it turn into caramel?
posted by RandyWalker at 5:05 PM on July 25, 2014

Response by poster: Wow. Now that I have a proper set of controls, it's _really_ easy to tell apart (and the powder in question was sugar, not xylitol).

Xylitol melts super easily into a clear liquid in a 250 degree oven. Sugar browns instead.

Comparing the xylitol control to the sugar in the solubility test, it was super easy to tell the difference.

Comparing the xylitol by eyes was really obvious too, I just wasn't convinced that there weren't brand-based differences in xylitol crystal size or color. The cream color is obvious to me with a control next to it, but not visible without.

Thanks all!
posted by freyley at 4:54 PM on July 26, 2014 [1 favorite]

Oh, thank goodness you've reported the results! We were just talking about this last night and I was ready to run some tests myself.
posted by maudlin at 12:15 PM on July 27, 2014