A dream of foam: better concrete, beer froth and ice cream

Oktoberfest in Munich is an exciting cultural event, but it is also a source of inspiration for materials scientists and engineers. Not the beer itself, but rather the beer foam is a source of inspiration.

A good head of foam -- generally measuring about 1.5 cm and containing an impressive 1,500,000 bubbles -- is supposed to be a sign of quality and freshness. Ideally, this foamy head remains stable, but several processes act to destabilise the bubbles: for example, liquid drainage of the foam, merging bubbles, or popping all can cause rapid destabilization. These are generic problems common to all types of foam, whether in food and drink or technologically advanced materials.

Undesirable change in the texture

One destabilisation process, in which large bubbles become larger and smaller ones shrink and eventually disappear, is particularly difficult to stop. Experts call this process "Ostwald ripening," named for German chemist and 1909 Nobel Prize winner Wilhelm Ostwald, who first described this phenomenon over 100 years ago.

Ostwald ripening causes an undesirable change in the texture of beer foam and foamed food products, and it weakens product performance in many other situations as well. Achieving foam and emulsion stability thus presents a challenge across a wide range of materials science applications, from personal care products to advanced functional materials. "Foams -- whether beer foam, ice cream or foam for insulation -- tend to coarsen due to their bubbles merging or ripening," explains Jan Vermant, Professor for Soft Materials at ETH Zurich.

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