Why do I have to put the hot chocolate in first?
April 11, 2014 10:03 AM   Subscribe

When I make instant hot chocolate, the directions always say to put the hot chocolate mix into the mug and then pour hot (not boiling) water on top. This does seem to produce better results than stirring the mix into hot water, although that might be confirmation bias. Does this actually work better? Why?

At the risk of being snarky, please don't just speculate; I'd really like to know and would prefer serious answers to people making guesses. Thank you!
posted by Mrs. Pterodactyl to Food & Drink (19 answers total) 9 users marked this as a favorite
The powder floats on top of hot water and then when you try to mix it, you have that much for of a chance of splashing hot water around.

When you pour water into powder, it emulsifies. You can also stop half way through and stir, without slopping hot water all over.

You do it when making concrete or mixing a liquid into a powder.
posted by Ruthless Bunny at 10:04 AM on April 11, 2014 [9 favorites]

In my experience, I always have difficulty getting all the powder to dissolve if I put the water in first. The powder floats on top and spills over the sides of the mug when I stir.
posted by rabbitrabbit at 10:06 AM on April 11, 2014 [2 favorites]

When I make hot chocolate with cocoa and hot milk, I pour a very small amount of hot milk into the mug, then stir the cocoa in to make a kind of paste, then pour the rest of the milk in on top and stir it in. This alleviates the floating-on-top problem and also the bits-stuck-to-the-bottom-of-the-mug problem.
posted by janey47 at 10:06 AM on April 11, 2014 [10 favorites]

It's messier if you put the powder on top. More of a chance for it to "poof" out of the mug when you stir it and most of it is high in the mug and dry rather than it getting wetted down before being stirred.
posted by cecic at 10:06 AM on April 11, 2014

The spoon plays a pivotal role in this. Powder on bottom doesn't cause the powder to stick and clump to the spoon. Powder on top and it always seems to clump over the spoon and spoon handle. More clumps results in more stirring and often more vigorous stirring. Thus, more mess.

I do what janey47 does. I always put the powder in the mug, add just enough hot water to be able to stir and make a paste with the powder, THEN add the rest of the water. The paste dissolves a lot more easily and smoothly than direct powder. No lumps, no mess.
posted by PuppetMcSockerson at 10:11 AM on April 11, 2014

Response by poster: Thanks for the responses so far; I have had the same experiences with clumping and dust poofing, but I'm really looking for a scientific explanation if one exists. I already know how to make hot chocolate I'll enjoy, I'm really just wondering what it is that happens differently when water is poured on top versus powder being stirred in, and based on my experiences and being very careful I don't think it's just the "poofing" although I could be wrong.

When you pour water into powder, it emulsifies.

This is helpful, thanks. Why does this happen when you pour water onto the powder instead of the other way around?
posted by Mrs. Pterodactyl at 10:16 AM on April 11, 2014

It's probably surface tension (that stops the powder from being stirred in easily when you dump it on top of milk or water.)
posted by needs more cowbell at 10:25 AM on April 11, 2014 [9 favorites]

I think the surface tension of the water accounts for the difference. Powder poured on top of water doesn't break the surface tension; water poured into powder doesn't have surface tension, so it is less cohesive.

(By the way, emulsification is not what happens here. An emulsion is a mixture of two liquids.)
posted by clavicle at 10:29 AM on April 11, 2014 [6 favorites]

Best answer: I'm really looking for a scientific explanation if one exists.

The force of liquid hitting the solid causes mixing, which makes more of the solid available to fresh liquid coming in, which does more mixing, which in turn makes yet more of the solid available to fresh liquid.

When you put solid on top of the liquid, only a small surface area is available between solid and liquid to mix. Using a spoon only increases the surface area a little bit, because a solid-liquid admixture sticks to the spoon and doesn't make way for much new surface area of solid to make contact with liquid.
posted by Blazecock Pileon at 10:29 AM on April 11, 2014 [10 favorites]

It's partially surface tension, but also that the powder manages to sort of keep itself dry unless agitated. I'm a slob, so I just make hot chocolate by heating a mug of water in the microwave and then adding powdered mix to it. The powder floats on top of the water, but also for the first couple stirs will basically encase itself in a sludge of chocolate paste - once you get a decent sized lump of powder submerged, the center is encased in partially dissolved powder and will start floating again unless continuously agitated. So, you can stir some of it in, but at first it'll just keep coming back up to the top until the lumps get small enough that there can't be a decent-sized pocket of dry powder at the center.
posted by LionIndex at 10:31 AM on April 11, 2014

Best answer: I'm really looking for a scientific explanation if one exists.

The ideal result of making a cup of hot chocolate is a suspension of powder in water.

If you pour the water onto powder, then all water in the cup has powder suspended in it.

If you pour the powder onto water, then not all water in the cup has powder suspended in it.

Some other things to consider: Most instant hot chocolate (the stuff you might buy at the supermarket - Swiss Miss and whatnot) is not just cocoa powder. It is a mixture of cocoa powder, dry milk, and sugar.

The different ingredients have different solubility and will react to surface tension differently.
posted by FAMOUS MONSTER at 10:34 AM on April 11, 2014 [2 favorites]

I've always thought that this works better because the hot water hits the powder and begins to dissolve it on contact, as opposed to the powder floating on top of the water and needing to be aggressively stirred to even begin to dissolve.

I find that adding liquid to a solid to produce a beverage always works better than adding a solid to a liquid. Even in the case of bagged tea -- pouring the hot water over a waiting tea bag begins the steeping process right away, whereas adding a dry tea bag to a cup of water requires a whole lot of dunking to get any progress at all.

The spoon plays a pivotal role in this.

This is a good point. The business end of a spoon is going to be at the bottom of the cup, so if the actual mixing in happens at the bottom of the cup rather than the top, you'll get better results. In a lot of ways this is probably more of an engineering type problem than a chemistry type problem.
posted by Sara C. at 10:47 AM on April 11, 2014

The hot water holds the powder down, melting the chocolate bits faster than if they were floating on top.
posted by myselfasme at 10:52 AM on April 11, 2014 [1 favorite]

If you don't measure the water before you heat it, pouring the water over the powder rather than the other way around also ensures that your mug is not too full.
posted by peanut_mcgillicuty at 11:11 AM on April 11, 2014

Best answer: This is the exact same reason why you add wet to dry in baking, and not the other way around.

Adding dry to wet causes clumping; the outer 'shell' of the dry payload gets saturated with liquid, protecting the inner core of dry material.

Also make it with hot milk, much tastier.
posted by feckless fecal fear mongering at 11:12 AM on April 11, 2014 [2 favorites]

Best answer: Science to the rescue!

Water is a great solvent for polar molecules. Sugar, table salt, and other small polar molecules are water soluble. When you put them into water, you get a sugar or salt solution.

Other molecules are not soluble in water. Most organic molecules with a carbohydrate tail are insoluble (unless they have a strongly polar active group, like the shorter alcohols). Starch and cellulose are not water soluble. Most plant matter is made mainly from starch and cellulose. (The exception are fruits, which can have more fructose than starch, but still lots of cellulose).

When you put non-soluble powder into water, you are not making a solution. You are making a colloid known as sol (solids dispersed in a liquid). If you wet salt, the water will dissolve the first layer, and the second layer will be exposed. If you wet a random non-soluble powder, the water will have to wash away the first layer before it reaches the second layer, so it is hard to make the suspension without vigorous stirring.

There are some special molecules which absorb water and swell. Starch, some proteins (gelatin) and some polysaccharides (xanthan gum) are common such molecules in the kitchen. When you wet them, the water gets absorbed by the first layer. This changes the viscosity of the layer, making it thick and clingy. This forms a clump. In the core are the dry layers of powder. They are held together by a bubble of the water-swelled substance. Outside of this bubble is the water. It can't wash away the bubble, because it is so viscous, it doesn't flow into the water. And the bubble protects the core of the clump from contact with water. This happens with starchy powders like flour, or also real cocoa powder. Tea powder is mostly dried cellulose, so it is also hard to dissolve.

Cocoa is very hard to dissolve. A cocoa flavored drink is a mixture of dextrose, cocoa powder, and other things (but mostly dextrose). In such a mixed powder, the water dissolves the soluble molecules (the dextrose), and the insoluble particles (the cocoa powder) which were suspended in the dextrose are now suspended in the water. No neighboring cocoa particles to cling to. So, no clumps, but an instantly homogeneous drink.

From here (edited a bit for relevance): http://cooking.stackexchange.com/questions/22648/why-do-some-powders-clump-in-hot-water"
posted by ananci at 11:17 AM on April 11, 2014 [10 favorites]

Best answer: There are two sets of forces at work, surface tension and chemical attractive forces. Surface wetting, how well the particles get covered in liquid, depends on both.

Surface tension happens because water really likes being close to other water molecules and generally isn't as attracted to other things (with a few exceptions). At the water surface, this means that the water molecules try hard to pull like molecules towards them. This means water surfaces are not flat, but bulge out, forming the familiar shape of a water drop on a piece of glass. So, water prefers to from convex surfaces. This effect "armors" the water surface and makes it tough to penetrate.

There are several kinds of attractive forces between molecules, some physical, some chemical. All molecules feel mutually-attractive forces that makes matter want to naturally clump up. For many kinds of molecules, these are small, and easy to disrupt. Powders, like your chocolate milk powder, will tend to form small masses of particles, clumps.

Particulate clumps dropped onto water, adding the powder to the milk, encounter a tough, flatish surface. On the microscale, most particulates are not smooth, but fairly pointy. When put on the surface of a liquid, they tend to have few points of contact. The surface tension effect with water is so strong that particles can do a waterspider dance, not penetrating the surface layer, touching only a a few points. They thus float around on the surface without wetting, coming into contact.

Some chemicals, like sugars and salts are very strongly attractive to water molecules, but many organic molecules either aren't that attractive to water to begin with (fats) or have parts that are attracted and attractive to water and parts that aren't (many carbohydrates). The water can wet one of these surfaces if the chemical attractive forces are enough to overcome the mutual water-water ones. In clumped powders, water may only be able to access the surfaces of the clumps, but, because the surface tension is so great, may not immediately be able to penetrate far. Thus, sticky clumps.

This is also why adding flour to gravy is a bad idea.

So why the recommendation to add a minimum of milk to the powder? That's done with vigorous mixing. More importantly, mixing of the powder directly with a minimum of liquid. Mixing mostly powder, efficiently fractures the powder clumps, allowing the water access to the surface, and to wet it. It's much harder to do this adding the powder to the liquid; mixing a full cup mostly just pushes the liquid around without breaking the clumps. This way, the chocolate powder is well-mixed by the milk, so when you add more milk the waterspider effect doesn't happen. No clumps.

Generally, multiple phase mixtures are termed dispersions. A colloidal dispersion of small solids in a liquid is technically called a sol. Blood and paints are also both sols.
posted by bonehead at 11:19 AM on April 11, 2014 [6 favorites]

Response by poster: Thank you! I do remember learning about water polarity in 10th grade so I have some context for that and the answers here make a lot of sense. Much appreciated!
posted by Mrs. Pterodactyl at 11:24 AM on April 11, 2014

Best answer: One thing I forgot to add, clumps float because, as well as solids, the gaps between particles are full of air. Irregular solids pack poorly, so typically at least half of the clumps are air. Because organic solids, like cocoa and flour, aren't that dense to begin with, the clumps float on top easily. Denser solids, like cements, tend to sink even with the air voids and so mixing is a bit easier.
posted by bonehead at 11:57 AM on April 11, 2014 [1 favorite]

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