Making a course gel

KS California strawberry yogurtTogether with a colleague, Joe Keddie, I am teaching a final year optional course called ‘Soft Matter and Biological Physics’. Joe is teaching the students about polymers; polymers are a classic part of soft matter physics. I am doing the biological physics part. It is good for Joe and I to make the module an integrated whole, so I talk about the importance of soft matter physics stuff like polymers to biology. Handily, there are many examples of this so that is easy.

Indeed there are so many examples, that I can’t get away from from them. After a hard week’s teaching I switched on the TV at home and awe an ad for a (new to the UK I think) yogurt called Liberté. This is being advertised as being very thick – they put it on a spoon, turn the spoon upside down and are proud that the spoonful of yogurt sticks to the spoon. This is called – in soft matter physics jargon – a gel. The yogurt is basically more than 90% water but it is solid (i.e., does not flow under gravity as water does) because of a network of polymer molecules immersed in the water holding it together.

These polymer molecules are naturally occurring polymers – Liberté’s makers are also proud of it being ‘natural’. One of Liberté yogurts sold by Ocado has a number of sources of polymers in the ingredients list. There are ‘milk proteins’. Proteins are naturally occurring polymers. One type of milk proteins is called lactoglobulins – these proteins are in the whey bit of milk, and they can form gels. The ingredients also includes ‘rice starch’ and ‘pectin’. Starch is a natural polymer made by sticking together many sugar molecules into a long chain-like molecule. Pectin is a similar molecule.

With all these polymers in it, it is no surprise that the yogurt is so thick, and as I type this it is on special offer too. 400 g of ‘creamy tasting’ polymer gel can be yours for only £1.09. A bargain.