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I've recently been learning about molecular gastronomy, and I was wondering - what edible substances do not dissolve in water, but do in other liquids (e.g. acid)?

In particular, I'm looking for something that can hold other things - for example, consider this hypothetical scenario: a glass of water in which float tiny spheres. You pour the glass into another bowl which contains some other liquid, and as they mix, the tiny spheres dissolve releasing the scent of some highly aromatic component they contained.

So, what substance can be used to contain something else, does not dissolve in water, but does dissolve in another non-poisonous liquid?

  • Is it important that the result is edible, as in not just non-poisonous, but also that the second liquid doesn't have too much impact on the taste? – Tor-Einar Jarnbjo Sep 22 '14 at 13:55
  • @Tor-EinarJarnbjo As this is cooking.se, we have to make the question about edible results. Else it would be off-topic and would have to be closed and possibly migrated. – rumtscho Sep 22 '14 at 15:57
  • @rumtscho That's true, but there are plenty of parts of cooking where the (tongue) flavour per se is not critical. I guess I'm not sure where to draw the line between "cooking" and "making something edible with food", as I've noticed a lot of molecular gastronomy stuff is focussed on style over substance - e.g. I saw some smoke-filled sugar spheres that I'm not sure I'd call food... – Benubird Sep 22 '14 at 16:18
  • Benubird: I think it would be easier to help you if you described more precisely what your intentions are. Is it necessary to use an acid, since the acid most probably will have impact on the taste or even have to be so strong, that the result is not really palatable? Or are you just looking for a way to release a "trapped" scent, so that it is irrelevant if the result is actually tasty? – Tor-Einar Jarnbjo Sep 22 '14 at 16:47
  • @Benubird I know that some of the stuff they do is not all that tasty, but the minimal requirement for this site is that the result is edible. We cannot accept solutions which will cause chemical burns or poisoning when consumed. Also, while solutions which have little to no taste are fine (because people could and in fact do consume such food :P), stuff which is non-toxic but tastes so vile that people would rather spit it out than eat/drink is also off limits. Food which looks showy but tastes meh is OK. – rumtscho Sep 22 '14 at 16:58
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If your question is specific about acid: Nothing.

The conventional way acids work is by dissolving them in water. I even have some vague memories that it's not technically correct to call a substance an "acid" before it has been dissolved in water - for example, pure HCl (a gas) is not an acid, but once it is dissolved in water, it becomes hydrochlorid acid. pH, the well-known measure for acidity, is defined as the logarithm of the number of protons swimming around in the aqueous solution - and before you dissolve the acidic substance, the protons stay firmly attached to their host molecule. I have never heard of an acid working without water being present.

I am not a chemist, and maybe there is an way to get acid to work using some other polar solvent instead of water. So I don't want to tell you that it's absolutely impossible to have an acid without water (although this could be the case, I just don't know). But:

  • The acid itself is by definition water-soluble. You can't bring acid and water two together and not get a new, weaker, acid-water solution.
  • I can't think of any edible polar solvent besides water. Ethanol could qualify, but most people don't consider 96.4% ethanol to be "edible".

If it doesn't matter to you what the other liquid is (not an acid), you can easily use anything non-polar. In food, any fat will do.

You could start by floating solid-fat spheres in water and then pouring them into oil. The problem here is that they will take quite a long time to dissolve (although this can be circumvented by using warm oil). The other way round will work better. Take something which dissolves in water quickly, and make the hollow sphere out of it. Float it in oil. Then you'll pour it into the water to release the fragrance.

Crystals are best for dissolving rapidly in water. I think that either salt or sugar will work well for your spheres. Of course, you are left with two problems: 1) how to manufacture the hollow spheres, and 2) what fragrance to use which will not dissolve the spheres themselves. For 2), you are probably looking at essential oils (warning, use foodsafe ones, not all are!). For 1), you probably need some precision candy-making techniques.


Update: letting food react with acid.

The answer above assumed that you are really looking for stuff which will dissolve in acid. The commenters pointed out that this is not necessary, as you can let the food react with the acid instead. It's an interesting idea, but it won't be easy to get done.

  • From the major food groups, you can exclude all proteins. We are made of protein, and any acid strong enough to quickly corrode spheres of gelatin or similar will ulcerate our mouths right away.

  • You can also exclude the sugars. They are water-soluble.

  • The polysaccharides are a better bet. Especially the hemicelluloses should be good candidates, as they are insoluble in water, and the result of the hydrolisis is edible (sugars and some polisaccharides). But they typically need very strong acids for the reaction. You might try to use a concentrated edible acid for the reaction, then dilute the result for consumption, but you'll have to pay lots of attention to proper ratio. Also, I don't know how you'll manage to physically shape one of the insoluble polysaccharides into a water-tight capsule at home.

  • The fats are also bad candidates. They are largely unimpressed by acids, in fact their most interesting reactions are with bases (saponification, etc.) The short unsaturated ones will probably react with an acid, but you'll need a fairly strong one, and the result won't really disappear.

  • The probably easiest way to do this is with salts. Especially the sodium salts tend to be edible and to react readily with acids. Plain old calcium carbonate sounds like a promising material, and with a bit of heating you can get it to react very quickly with acid solutions dilute enough to drink afterwards. Again, you have the problem of somehow making spheres out of it.

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    while this is true, adding concentrated acid to water holding something that won't dissolve in water could produce mediumly-concentrated acid that will dissolve the substance. – Kate Gregory Sep 22 '14 at 12:56
  • @KateGregory I don't understand your comment. The whole point of what I wrote is that whatever dissolves in a water-acid solution will also dissolve in pure water. So, it's not possible to add something into water, have it not dissolve, and then add acid and have it dissolve. – rumtscho Sep 22 '14 at 13:04
  • but that's not true, at least not of non-food items. Metals will dissolve in strong acid but not in water. The experiments with Coke and teeth are also examples of dissolving in acidic solution but not in pure water. – Kate Gregory Sep 22 '14 at 13:12
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    @rumtscho: Even if Kate's wording is incorrect from a scientific point of view, her practical reasoning is correct. For example, if you add aluminum to an aqueous solution of hydrochlorid acid, the acid will react (not dissolve) with the aluminum and create aluminum chloride, which will dissolve in water. It may appear as if the acid dissolves the aluminum, but this is technically not quite correct. If you add aluminum to pure water, there will be no obvious reaction. – Tor-Einar Jarnbjo Sep 22 '14 at 13:50
  • @Tor-EinarJarnbjo Thank you for pointing that out. Indeed, the wording had brought me to think of literally dissolving the material in the acid solution, not of letting it react with it. And you are right, from a practical point of view, it doesn't matter to the OP if the acid dissolves the spheres or reacts with them. – rumtscho Sep 22 '14 at 15:59
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Coming from a purely culinary background, aromatics and dietary compounds are generally referred to as being:

water soluble (Vitamins B and C tend to be water-soluble); fat soluble (Vitamins A, D, E, and K); and alcohol soluble (such as some compounds found in tomatoes brought out by alcohol, which is why wine and italian foods become an adventure for the palate)

You may want to consider crossing those barriers, as well, since they operate more on the molecular level.

And from another perspective: Almost all of our food is acidic. Acid = Tasty. Tomatoes, Balsamic vinegar, chili powder, etc, etc. If you turn out a basic food, it is going to have a very flat and unpalatable taste, which is why baking soda is used very sparingly when it's needed.

You may want to contact the author of, "On Food and Cooking", as he may be able to help out with your task. His book is excellent and heavy on the science.

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