The Science of Frothing Milk with Dr Helen Czerski

Which is the best milk, and at what temperature, for maximum froth in your hot chocolate?

During the encore of our 24 hour show, Nine Lessons and Carols for Socially Distanced People, Dr Helen Czerski mentioned something about milk froth. Unbeknownst to us this started a conversation in the live chat and one viewer sent in a question about it to our Sunday Science Shambles Q&A show. They wrote, "At the Nine Lessons - The Encore show, you mentioned you did some milk frothing experiments. A few of us at the live chat got really excited. Would you be happy to share the details + findings with us? And maybe the science behind milk microfoam formation too?"

So instead of just answering the question during the show Helen decided the only way she could answer it properly would be to spend a month thinking about and then a weekend collecting data and doing a proper experiment. So here are the results and some of the science behind it.

[John.z]

Ah, bubbles. Your thesis with yet another applications. Excellent.

[Marklek]

Remember that it costs a lot of water to make a single almond. About 1 gallon of water per almond of California water each, IIRC. That’s a huge environmental cost you are exporting to a very water sensitive area.

[deanfielding]

I think I might need to repeat this experiment using a steam frother.

[nicholaskirwan]

Loved it. What a way to spend a Sunday afternoon. Well done HC.

[AshArAis]

I had read that barista oat milk used sugar in place of protein to create foam, though your analysis says fat. I choose oat milk for health (less cholesterol), and at home I use the no added sugar even though it's less foam. It's still tasty, and when I get coffee at a shop the barista version is a nice treat! Thanks for doing the video

[zapfanzapfan]

Whipped cream "melts" when put on something hot so I assume high temperature is bad for making small milk bubbles.

[johncoach]

A 'steamer' would also introduce air as it works. Could you feed air into the milk a the same time as the 'whipping'? For yourself, just use a straw and blow a bit in as you whisk.

[superfluidity]

Very interesting video. I'm curious about how the air gets in using that frother, which looks like it's fully immersed as it works. Maybe it makes enough of a vortex to open itself to the air surface? Would be interesting to see what happens with other foam making methods like a cafetière or steam wand. Might be hard to make the steam wand technique precisely repeatable. And you can't photograph it so easily in a steal jug.