Why coffee milk bubbles

Why coffee milk bubbles and how to avoid it

Monika Fekete investigates why milk bubbles form and how they impact on coffee quality and presentation.  Recently, I watched my coffee go cold in front of my eyes. It had been two months since I had enjoyed a proper coffee. I was looking forward to the experience as I sat at one of my favourite local cafés. However, no sooner had my coffee arrived, my newborn baby decided to test out his lung capacity and I found myself trying to calm him.   I had hoped this situation would be a one-off, but sadly it is not. My tiny son senses precisely when his mum is about to take a moment to enjoy her coffee, and duly demands attention. Consequently, I have had the opportunity to watch rosettas getting swallowed up in bubbles that slowly appear on top of my silky flat white. Interestingly, this wasn’t always the case. Sometimes many large bubbles emerged on the surface almost immediately, sometimes the micro-foam held together even after five minutes. 
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Coffee science

Proteins with purpose: why milk curdles and how to avoid it

If you regularly make soy coffees for your customers, you have probably noticed that soy milk is often harder to work with than dairy milk – it tends to curdle more in coffee, especially when steaming hot. With some coffees it behaves well, with some it doesn’t.  The delicate protein structures in milk are to blame for the curdling effect.  Proteins are long, folded chains of amino acids. Humans only use about 20 different amino acids, and they can be linked after one another in any order. Most proteins contain hundreds of them.
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