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Steaming the perfect milk for coffee

Baristas and brewer’s, stand-by, as this guide bypasses begrudged, black coffee drinkers and searches for the ideal milk to complement the perfect coffee!

Understandably, milk is an option in coffee, and the type you choose may differ, so there will be divided opinion. So, we’re hoping to use science to strengthen the argument.

Now, we’ve already examined what the best non-dairy milk for coffee is but does dairy milk possess attributes beyond what plant-based milks can conjure? There’s only one way to find out.

Does the milk matter in coffee

What makes milk different?

Besides the colour of the lids,(skimmed – red lid, semi-skimmed – green lid and full-fat – blue lid), milk is made up of three main components: proteins, carbohydrates and fats.

The levels of the three differ, depending on how each farm produces their milk. Factors like the conditions the livestock are kept in, what their diet consists of and how the milk is treated after it’s been extracted can all impact upon the flavour, texture and performance of the milk.

Furthermore, milk differs due to its make-up. Skimmed and semi-skimmed milk, for example, have a greater ratio of proteins to carbohydrates and fats, whereas full-fat milk outweighs in the fat department.

It’s the protein levels which make the milk differ in performance, for a barista. The rate at which the proteins react when heated or steamed contributes to the level and type of air bubbles created, leaving a lasting impact on the frothiness, thickness and overall creaminess of the milk.

The science of milk

It’s no accident that the coffees you are served come with alternate looking aesthetics. From the stiff quiff of a cappuccino to the multitude of colours contained on top of your latte, it’s largely down to the quality of the milk used.

A lesser quality milk will produce a distinct lack of frothiness and a disappearing act before your coffee cup even makes it to your lips! Again, it’s down to the proteins, but more scientifically, it’s  the types of protein that matter.

Casein and serum (whey) are the two key culprits which can influence the performance and flavour of the milk, once heated.

The former impacts upon the texture. Casein form what are known as ‘micelles’ and, once air bubbles are injected through the milk steaming process, they become disrupted. Molecules then surround the air bubbles and prevent them from bursting, creating foam, as we know it.

Serum, on the other hand, is responsible for the flavour. Once heated (or cooked) the flavour can transcend dramatically, hence why it’s crucial not to overheat the milk during the steaming process.

What happens when you overheat milk?

Technically, when you steam (heat) milk over 100 degrees centigrade it causes a reaction known as the ‘maillard reaction’ resulting in the lactose and caseins forming an ‘amadori’ product.

Amadori dehydrates and oxidises, during the reaction and produces a loss in nutritional value and unorthodox flavours we’re not used to.

On top of this, the milk fats (in the form of saturated, monounsaturated and polyunsaturated fatty acids) are also responsible for the flavour and finish, after heating. Similar to how the casein forms molecules, fats do too, stabilising the formation of the foam. The higher the fat content – the more stable a foam is at below room temperature. In comparison, milks with less fat are more stable at higher temperatures.

What is the best coffee for milk?

Each element of the milk contributes to its ability to froth, foam and add flavour. Arguably, whole milk has more proteins and fats so will perform better because of the caseins and serum.

Much like how the origin of your coffee bean can determine the roasting, brewing and flavour of your coffee, the same can be said for milk. Hence why there are some brands which baristas preferfor their take on the ‘perfect coffee’.

The search for the perfect milk will probably differ, depending on a baristas opinion and the steamer they use. Some steamers may stretch the milk better than other, creating varying levels of foams and froths.

Does the milk matter?

Scientifically, I think we can agree that the milk does matter. Understanding the properties of milk will definitely help to improve its performance in a coffee.

However, to fully appreciate our milk choices, perhaps maybe it’s time to consider them with as much as attentiveness and diligence as we do when researching a good quality coffee.

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