Hydroxypropyl Methylcellulose: The Properties (1)
"...if you want thickening plus foaming or thickening plus thermalgelation, consider using just the one HPMC rather than two or three different ingredients".
First, it becomes soluble in cold water. So, water insoluble cellulose is converted to cold water soluble, hydroxypropyl methylcellulose.
Next, depending upon the length of the cellulose chain, it will thicken water (and alcohol). This thickening can be slight, thinner than 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 mean thin (5 -100), high numbers mean thick (200,000 +).
Interestingly, in the case of hydroxypropyl methylcellulose and methylcellulose the colder they get, the more soluble they become.
All HPMCs are soluble in cold water, but have different responses when you try to dissolve them in warm or hot water. If you disperse in hot water then cool, the temperature at which the viscosity (thickening) kicks in will vary with the grade; the K and E types thickening below 48C (120F), F types below 35C (95F).
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 hydroxypropyl methylcellulose? None of the above have a range of viscosities, from extremely thin (5mpas) up to extremely thick, (200,000+ mPas), which makes hydroxypropyl methylcellulose and its ‘sister’ methylcellulose, really versatile, as regards thickening ability. The mouthfeel also changes with inherent viscosity and the temperature. They are beautifully clear, colourless and tasteless. And that’s before you get to the other properties. So, if you want thickening plus foaming or thickening plus thermalgelation, consider using just the one HPMC rather than two or three different ingredients.