Curious curdling casein

In September 2013 on September 27, 2013 at 7:12 am

milk and lemon 25Sept

Kirsti: Last night I wanted a milky honey drink, and thought I would sneakily sneak a little bit of lemon into it too.

Having previously experienced the curdling disaster of squeezing lemon into a creamy sauce, what I’m about to describe sounds ridiculous. Somehow, I thought I could get away without curdling my milky drink with my drops of lemon.

As I dripped the lemon in and hoped for the best, in the back of my mind I knew what was going to happen. My drink – which was boiling water, milk, honey and a few drops of lemon – curdled immediately.

Surprise, surprise. Not!

The curdling happened because the heat sped up the reaction between the clusters of milk protein (called casein micelles) and the citric acid in the lemon. Instead of being repelled from each other as they normally are in fresh milk, the micelles rapidly glumped (yes, glumped!) together. Bummer.

Temperature is a fabulous catalyst – it gets chemical reactions going quicker and more efficiently.

So I decided to do a little (non-replicated) experiment, and tried again with cold water.  No lumps!

But it turns out that even cold milk eventually curdles. The casein micelles start loving one another, a little bit at a time, albeit FAR slower thanks to the temperature of the drink. Happily, the teeny tiny little curdles that eventually occur in your cold drink will probably not put you off drinking it, if you detect them at all.

But I still have a problem: in cold milk and water, the honey doesn’t dissolve….ahhh, there goes science again!


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