Hydroxypropyl Methylcellulose: The Properties (3)
Interesting properties: polymeric emulsification
You know emulsifiers? They work by having one end of a short molecule water-loving, the other end fat-loving. So, one end attaches to water, the other to fat or oil, enabling emulsions to be made.
Now imagine this not as a short molecule with two different ends, but an enormously long chain, like a deep sea fishing line, with little hooks all along it. Some of the hooks are water-loving, some fat-loving. This is a polymeric emulsifier… a polymer that emulsifies all along its backbone but, because it is a long chain, it also stabilises the emulsion by thickening the water phase. Whilst MCs are incredibly good at this, HPMC is also pretty good, making an emulsion from about 2% oil (which is basically an oily foam) up to about 60% oil, which is a lot like a mayonnaise.
Mostly HPMC emulsions are seen when folks are making dairy free whipping and cooking creams. Here the cold viscosity, emulsification and foaming abilities all come together to make an emulsion that will whip to produce whipped ‘cream’ or stay stable when heated like cooking cream. Often when making one of these dairy free toppings, the manufacturers will combine two HPMCs, one thick, one thin. The thick one will, surprise, thicken the water phase of the cream, reducing the movement of the fat globules, thereby reducing creaming (fat at the top, water at the bottom) and coalescence (where the small fat globules join up to form bigger ones). The thinner one will be better at film forming and foaming. The film forming part will reduce the ability of the fat globules to join up, reducing coalescence, the foaming will help with the whipping, increasing the overrun (amount of foam volume).
The advantage of this combination of two HPMCs is that they only need to declare one ingredient on the label.
Interesting properties: film forming
A clear, flexible, edible film.
You can coat tablets with it, to help them slip down the throat… and let’s be honest, stop all the powdery bits inside from falling out. Or make it into capsules that dissolve in the stomach. Both pharmaceutical applications.
But, you can also make glazes on buns that are allergen free and films on the outside of fried foods that reduce the oil uptake when the food is fried – without compromising the eating texture, and for the cupcake lovers amongst us, edible glitter.
All you have to do is dissolve the HPMC in water, then dry it. Of course, it’s a little more complicated than that. Lower viscosity ones are better and you need to be aware of drying temperatures and times, but basically that is it.
Bear in mind the dissolution temperatures; HPMC will dissolve in the mouth but MC won’t.
Interesting properties: foaming
Sometimes a nuisance, sometimes a joy. The same properties of water-loving and oil-loving areas on the backbone means that this stuff also has surfactancy. That means that solutions with no oil in them will foam. The oil-loving (water hating) bits simply migrate to air interfaces rather than hang out with the water.
It can be a pain of course, when you don’t want a foam, but there are ways around that.
For me, the real joy of working with HPMC foams was that the foams are fat stable. Most protein foams will break down when there is the slightest amount of fat present. If you have some yolk in egg white, it is useless for foaming – lower overrun and not stable when heated. HPMC will simply emulsify the oil into the foam and will be stable. I’ve made chocolate meringues that contain 16% real chocolate. Get in touch if you want more details. They can be egg free or contain egg white.
Let’s not go to marshmallows just at the moment, the sugar level is usually too high for HPMC to cope.