Why does milk bubble in your coffee?

It is the age old questions – why does milk bubble in our coffee? Does it mean that your coffee has gone cold? Or is it an indicator that your coffee is stale? Well, let’s find out!

There was an experiment done on coffee milk bubbling by Monika Fekete from Coffee Science Lab and she has uncovered the answers for us. When air is injected into milk, the milk proteins surround the air bubbles and protect them from bursting, giving you a micro foam that is used to make your coffee (you know what I am talking about, that delicious, silky looking milk that sits on top of your latte). The micro foam naturally breaks down over time due to gravity pulling it downward resulting in the bubbles appearing in your milk. That’s the lowdown, however, if we use a different style of coffee or different milk is there a different outcome?

The answer – a resounding YES! If you are a skinny milk lover, unfortunately bubbles will form in your beverage three times faster than that of full cream (who’s ready to make the switch?!) The same results happened when they used homogenised milk. But, when un-homogenised milk (where the layer of cream is still present at the top of the milk bottle and not removed) gave the best results and was able to retain the silky milk for the longest time. The results of this testing highlight that milk with a higher fat content is able to retain the silky milk finish longer than that of skinny milk. I guess it’s true what they say, fat = flavour!

When they looked at the roasting profile of coffee to see if it played a role in bringing on the milk bubbles sooner, it was discovered to have no impact on bubbling effect. In both a dark or light coffee roast, the bubbling only began to form around the 2 -3 minute mark. However, the freshness of your beans WILL have an impact. The fresher the coffee, the quicker the bubbling will come on. The reason? Older coffee won’t release as much carbon dioxide upon grinding unlike fresh coffee.

So if the bubbling in coffee drives you mad, here’s how to avoid it:

• Drink full fat milk or better yet, un-homogenised milk which holds the silky milk finish for longer
• Use older coffee has less bubbling

Let’s face it, a good coffee- skinny milk, almond milk, or full cream milk is all subjective. As long as it’s St Remio, you know you are on to a winner!

References:

Feteke, M 2019, ‘Why coffee milk bubbles and how to avoid it’, How to – Bean Scene Magazine, viewed 5^th June 2019, <https://www.beanscenemag.com.au/why-coffee-milk-bubbles/>