I started editing my Two recipes post (previously) and as I started going on and on, it struck me I had a lot to stay, so I figured maybe a separate post would be a good idea.

Mixing and stirring liquids – a chemist’s son’s guide


As chemists, Dad and I came up with a bunch of from-the-lab methods of smoothly or thoroughly mixing different ingredients in the kitchen. Since texture in cooking and preparation are often so important, I thought I’d share some of these techniques and principles in this post. I am no longer a professional chemist, but I still use these techniques in my own kitchen.

These are all tips and tricks designed around knowing your ingredients and knowing how to work with them or at least preventing them from working against you.

General miscibility principles

I’ll start with a little guidance on how to think about ingredients from a chemist’s viewpoint and how they’re likely to get along in the same mixing vessel. The important secret is that with a very few exceptions, it’s all about oil and water.

  • Between these kinds of ingredients you are likely to actually dissolve (as opposed to having granules of ingredients floating around in each other, but not dissolved) your ingredients into one another
    • Oil and oil-based powders (in cooking usually cheeses and nut-based meals, but also most herbal flavors are conveyed by highly flavored/scented fats and oils) mix well together.
    • Water and water-friendly powders (in cooking, usually sugars or salt) mix well together.
      • Mixing with hotter liquid is usually easier, though you might not always want to heat your liquid if mixing in the kitchen.
  • These are poor mixers:
    • Oil and oil-based powders DO NOT mix well with water and water-friendly powders.
    • Except with emulsion (see below).
  • Here are some things that may help:
    • Mammal milk and nut milks are an emulsion of oil and water and tend to mix well with both oil-based and water-based liquids and solids. This also holds to some extent for other dairy products like yogurt and soft cheeses.
    • Alcohol can also make it easier to mix water-based and oil-based substances together, but not as well as milks.
    • Acid can also help with the immiscibles, but it’s not great at it. Acid is better as an emulsion stabilizer (see below).
    • Heat can also help oils, especially essential (herbal, flavor) oils mix well, but be careful of overcooking – it can be easy to do with essential oils.
  • And some special cases:
    • Starches don’t dissolve in waters or oils but do get wettened by them and can make pastes or doughs.
      • I won’t go into how that works, but there are all sorts of happy complicated things that happen in doughs, pastes and pastries.
    • Eggs are interesting too.
      • Yolks tend to get along well with fatty ingredients.
      • Whites are a little better with the water-like ingredients.

General mixing technique

There a number of different mixing methods out there, but I think it helps to think about them when applied to liquids, then generalize them to powders and mixing powders into liquids. Everyone knows about stirring, but I don’t think it’s obvious that there are different ways to stir the same mixture and that some stirring techniques are more or less efficient depending on the different results you want.

For instance, take mixing a slightly heavier, thicker fluid into a thinner one, like sugar syrup with water. If you just pour the syrup in first or last, you’ll find that most of it won’t mix, but the heavier syrup will lay at the bottom of your vessel in a coherent layer.

A common way to mix the two liquids would be to stick a spoon in there and swirl it around. It turns out that that method is pretty inefficient. After the initial chaotic part, both liquids start to follow the circular path of the spoon and don’t mix very quickly. When you want the combination to be quick and thorough it’s a better idea to really create some chop within the mixture. So instead of swirling, try quick movements from side to side in the vessel. Or at the very least, do a figure 8. The idea is to cause a lot of disturbance in the mixture, not just get it all moving in the same direction.

Similarly, when mixing two powders together, the best way to get a really good mix is to pull or push the powders vertically through each other. This chaos is what really what you need for a good mixture to distribute the ingredients evenly through each other.


Mix a powder into a liquid

This is not required for powders that easily dissolve in the liquid (like sugar in water), but you could certainly practice this technique with sugar and water.

As a less trivial example, let’s take a look at cocoa mix (sugar, cocoa powder, spices) with milk. The sugar will mix well with the water part of the milk emulsion, the cocoa powder with the fatty part of the milk emulsion. It’s still not a trivial mix as you may already know. The best way to do this and avoid having clumps of unmixed powder in your hot cocoa is to do the following:

  1. Take the entirety of the powder you want to mix and put it in the vessel you want to cook it in or drink it in (if you can put it in the vessel you’re planning to drink from, you’ll reduce the loss of your drink to surface tension sticking the mixture to your other vessel).
  2. If you can, heat your liquid. If not, that’s okay too, you just have to be more careful to look for and mix out lumps.
  3. Add small portions (small splashes, teaspoons or tablespoons) of the liquid at a time into the powder and mix each portion thoroughly into the powder. What you’re going for here is a smooth, well-mixed paste. It’s okay if the paste mixture starts out clumping up. It’ll smooth out as you go further. Mix the paste with the liquid, thoroughly and vigorously, with a chopstick or a bamboo skewer or a small spoon at every opportunity.
  4. When the paste gets significantly wet and fluid, add larger portions of your liquid, still mixing thoroughly at every add, until your mixture is complete and thoroughly mixed.

Mix the Immiscibles – Emulsion

Immiscibles are, classically, oil and water. In cooking, you more generally see oil and vinegar dressings. By immiscible what I mean is even if you stir the hell out of it, the mixture only stays mixed for a very short time and if you let it stand, it will separate out on its own.

There are ways to stabilizing this sort of mixture. One way is to mix it really well, like in a blender or with a whisk. Even so, this is difficult to achieve without care. Most of these kinds of mixtures in the kitchen are done with a high speed mixer, patience, and a small trickle of oil into a small quantity of the mixture. This kind of mixing will help take much longer to separate (compared to a shaken/stirred oil and vinegar salad dressing) and is called an emulsification. Milk and mayonnaise are both emulsifications that are very stable. To make an emulsification of water and oil more stable not only do you just mix the heck out of it, but you also add a stabilizer.

Common stabilizers for food prep:

  • egg yolks (lecithin)
  • gelatin
  • skim milk (casein)
  • mustard (lecithin, acid)
  • cayenne pepper
  • onions
  • any acid (sparingly) – like lemon juice, vinegar


Mixing Miscible Liquids (soft drinks):

In drink mixing, you often need to mix different kinds of relatively miscible liquids together. Mostly this works fine, but even among the miscibles, it can be non-trivial to mix them together. Take for example mixing a viscous sugar syrup or molasses into iced tea. There are ways to reorder what you mix into a drink when, as well as simple mechanical approaches that will help mix the liquids thoroughly.

Thermodynamics (Heat):

Heat will help you mix more and less viscous liquids. Sometimes it’s worth it even if you want a cool drink outcome to use a little hot liquid to help dissolve the two liquids within each other, then cool the mixture down again with ice or refrigeration.

Mechanical (Agitation):

Like I said near the beginning of this article, vigorous mixing will also help mix your liquids well together.

NOT Mixing Miscible Liquids:

There is a common and a not-so-common method of pouring miscible liquids so that they don’t actually mix. You’ll see this done to get multilayer alcoholic drinks. Other non-alcoholic  examples are restaurant style Thai iced tea and caffe lattes where the barrista goes out of her way to make sure that the coffee or tea and milk don’t mix very much.

The point of all of these techniques is to pour the lighter liquid over the heavier one and do it in a way that disturbs the underlying liquid the least. So you need to experiment or look up the “specific gravity” or density of the liquids you plan to pour on top of each other. The heavier ones go on the bottom, the lighter on top. It may help to remember how you’ve seen others pour the drink you’re interested in making, to look up a recipe, or to keep in mind that in general things with other things dissolved in them have a higher specific gravity and are heavier, so syrups or even sweetened tea are likely to be heavier than cream or water. Also milks and fats tend to float on top of waters. So do frothy things that have a lot of little air bubbles mixed in.

The other trick is to know that friction works between two different liquids just as it works on solids, so the technique here focuses on keeping the flow of the pouring liquid both to itself (and not creating turbulence with the fluid underneath) and on slowing the pouring liquid down so it’s less energetic when it touches the liquid below. Finally, the more you can redirect the flow of the pouring liquid so it doesn’t go directly down into the underlying liquid the better. This is a little counterintuitive when I say that the best methods seem to include slowly pouring the upper liquid down the side of the glass, but if you look up close at how liquids adhere to glasses, you’ll see that surface tension makes a little ramp that the upper liquid should follow so that its ultimate flow skims along the surface of the lower liquid.

There are a couple of methods that I find work better than others, and it also helps to know which liquid is denser than the other, if the difference is significant. If you know that, you can pour it first, which helps the physics of the non-mixture and helps prevent problems.

The bartender’s classics are the pour down the side of the glass and the pour down the back of a spoon. I find that pouring down the side of the glass doesn’t work so well unless you are really careful or there’s a big difference in density or miscibility between your two layers. I think this is because even if you can pour down a tilted glass wall, you still get a significant velocity and intermixing at the glass wall. The easy to miss detail that’s really vital about using a spoon is the same as the chemist’s method of using a glass rod: The tip of the spoon blade or the tip of the rod MUST touch the glass’s inner wall. Surface tension makes sure that a gentle pour along the rod/spoon handle stays stuck to the rod. Where the tip of the spoon or the rod touches the wall, surface tension again assists in redirecting the flow down the side of the glass and ultimately to the top of the lower layer.

Here’s an article that shows the back-of-the-spoon method. Here’s another that talks about using an iced tea spoon handle much like the rod I was writing about.

Finally, it occurs to me that colder liquids are generally more viscous, which would mechanically help keep each layer together.

Any of these methods will take practice, so practice and have good friends drink your mistakes!

Mixing powders:

As you would expect, heavier powders tend to sink to the bottom. So do larger objects, so when you mix two powders, if you do it poorly (at least for the first few days of mixing) the smaller granules will rise to the surface. When mixing powders, you want to create a lot of vertical motion to keep the distribution of smaller and larger granules homogeneous.

Anyhow, I think this is about all I can put down on “paper”. Feel free to ask questions if you’ve got ‘em. Or clarify. :)