Coffee. It’s one of those things that you love or you hate. It gets you up in the morning. It’s good when catching up with your mates. It’s a comforting hug in the midst of winter. But have you ever wondered about the science behind it all…?
My relationship with coffee began around 2 years ago. After disliking it for a number of years, I was offered a cup on my first day of a new job. Startled and not wanting to look rude I said ‘Of course!’ – leading on to getting one every morning for the rest of the summer. And by the end I loved it! (and maybe relied on it just a little bit).
Coffee ultimately consists of two main ingredients; the espresso shot – and if you are not a hardened professional – the milk.
Milk is an important part of any coffee and can lead to a variety of drinks – you’ve got your cappuccino, latte or if you hate any type of foam, a flat white.
The milk is heated by the barista with a steam wand in a process called stretching. Stretching adds heat, water and air into the milk. The air is sucked into the mix from the outside through the whirlpool that is created by the wand.
The milk itself is made up of a whole family, including sugar, protein, and fat.
The sugar in milk is lactose and is what sweetens the drink, and makes the coffee taste less bitter than if you just had the shot straight. The human tongue also more sensitive to the sweetness of lactose when it is heated, which is why coffee tastes sweeter when it is warm.
There are two main types of proteins in milk. Caseins make up 80% of the mix and whey proteins take up the remaining 20%.
The heat of the steam wand breaks down these proteins and causes them to denature. Each end of the protein either likes (hydrophilic) or dislikes (hydrophobic) water. Due to the heat they unravel and form a chain, which is called adhesion which makes the foam nice and stable.
The air which has been pushed into the milk from the steam wand acts as a safe house for the ends of the protein which don’t like water. All these ends gather up and take refuge inside the bubble. Likewise the other ends hang out on the outside. This stabilises the air bubble and helps keep it around.
However, anyone who has made a coffee before knows that foam that is too stable is not a good time.
There isn’t anything quite like trying to make latte art with low fat milk and just watching it fall out of the jug in a huge lump of foam.
This is where fat comes into the mix.
Like proteins the fat in milk also have hydrophilic and hydrophobic ends. This means it’s a battle between them to who can get the air bubble first. However fat doesn’t like hanging out with one another like the proteins do and so the foam becomes less stable with the more fat content you have. However the fat molecules begin denaturing about 40 degrees Celsius and so foam begins to stabilise again after this point.
Fat is also important in coffee as is gives a better ‘mouthfeel’ to the drink. This where the fat melts, giving the drink a silkier, nicer feel as you drink it. Fat also blocks out some of the more bitter tastes of the coffee and instead brings through the nutty, caramel flavours (if you believe in all that jazz). The flavours stick to the fat which allows a nice slow release for them.
So there you have it, the first element of coffee SCIENCED!
Stick around for more coffee explanations – Fridays and Sundays. Just in time to enjoy with your morning coffee.