Interesting Properties: Thickening

First, it becomes soluble in cold water.

So, water insoluble cellulose is converted to cold water soluble, methylcellulose.

Next, depending upon the length of the cellulose chain, it will thicken the water (and alcohol). This thickening can be slight, like lemonade; thick, like runny honey or seriously thick, stand-spoon-upright-in-it thick. This thickening can be measured, usually using a rotating disc that measures the force that is needed to make it spin in the solution. The ways that solutions react when stirred has spawned a whole subject in itself, called rheology. The instruments used to measure it are rheometers. The term used to describe the amount of force you need to move a fluid, under controlled conditions, is viscosity. However, viscosity and viscous are often used casually just to mean thickening. Viscosity is quoted in milli Pascal seconds, mPas-1 or centipoise cPs. Low numbers means thin (5 -100), high numbers means thick (50,000 +).

There are lots of food grade thickeners on the market – guar, locust bean gum, pectin, xanthan gum with a more natural origin. Why bother with methylcellulose? None of the above have a range of viscosities, from extremely thin (5mpas) up to extremely thick, (200,000+ mPas), which makes methylcellulose and its ‘sister’ hydroxypropyl methylcellulose, really versatile, as regards thickening ability. And that’s before you get to the other properties.

Methylcellulose: The Properties (1)

Interesting Properties: Unique; reversible thermalgelation

This is a really weird one and counter-intuitive to everything most people understand about gums and gelling agents.

The colder a solution gets, the thicker it gets. Quite normal except that these gums don’t require heating to dissolve them, which is unusual. However, once they are dissolved, if you heat the solution, first it thins down a bit (normal for all thickening systems), then as the temperature continues upwards, it solidifies. A little like an egg white, turning from clear and thick to white and solid. This is not unique. Egg white does it! We call it thermalgelation – gels on heating.

The bit that is unique is that if you cool it down, it will return to liquid again. The transition is reversible with temperature. Reversible thermalgelation. Now that is unique.

If you heat it again, it will solidify again. Then return to liquid on cooling…

And on, and on. As many times as you care to do it.

The methylcellulose solutions’ response to heating is a physical one; a phase change not a chemical one. Phase changes tend to be reversible; chemical changes are permanent. So, a boiled egg stays ‘boiled’ or gelled, because its chemistry is changed by heating. Methylcellulose gels when heated but returns to liquid on cooling because the change is physical not chemical. Think ice, water, steam, water, ice…. Physical changes.

The strength of the thermalgel, whether it is sloppy like an egg white just changing or rigid and cuttable, depends on whether you are working with hydroxypropyl methylcellulose or methyl cellulose, the concentration used and the temperature and time of cook.

Methylcellulose gives the strongest hot gels (thermalgels) which makes it incredibly useful for making vegan burgers (sticky in the cold to hold all the ingredients together, solidifies on heating to give bite). Hydroxypropyl methylcellulose has a much softer hot gel – useful for gluten free bread, stopping potato croquettes from exploding in the fat fryer and stopping pie fillings from baking out.  If you want to talk about hydroxypropyl methylcellulose, either get in touch or look elsewhere on this site where I’ll discuss both these and other applications, guiding you through which type and how much to use to achieve which ends results.

Continues

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