Preparation of Gels
We are familiar with jams, jellies, cheese, curd, boiled egg-white, tofu, bath gels, hair styling gels, soft contact lenses, and many such substances. These substances appear like solids, but they are softer and sometimes spongy. This kind of substances scientifically belongs to the class ‘gels’ (from the latin gelu – freezing, cold, ice or gelatus – frozen, immobile). A ‘gel’ is a colloidal system in which a liquid is dispersed within a solid where the solid is the continuous phase and the liquid is the discontinuous phase. Despite this, gels are typically 90 – 99.5% liquid in volume. In fact, gels consist of a porous, continuous network structure formed from the colloidal particles in the entire volume of the liquid medium and the liquid filling the pores. Gels are used as stabilizers and thickeners in many food products like in sorbets, pies, ice creams, curds, cream cheese, fruit confectioneries, etc. In food products, gels are used to provide structure, stability, and spaces for holding flavours, sugar, oil, etc. Gel is used as bacterial growth medium in microbiology laboratories. Gels can be made from polysaccharides (e.g., starch, agar, pectin, carrageenans, and alginate), proteins (e.g. gelatine, keratin, casein, and ovalbumin), etc. Here, we shall prepare gel by using polysaccharide agar-agar. Use of agar-agar in several East Asian culinary traditions has been known for over three hundred years. The word ‘agar-agar’ means ‘jelly’ in Malay-Indonesian language.