Grinding on the dance floor.

Last week we talked all about the science of milk, this week we are moving onto the other important ingredient in coffee – the espresso shot.

The shot is one of the vital parts of the drink. Messing this up will either leave you with a sour or bitter taste in your mouth (good milk can cover this up but only so much).

The shot process begins by grinding the beans into one of the portafilters.


The portafilter is what sits in the machine and what the shot pours out of.

The actual grind (how big or small the individual coffee grinds are) of the beans can be adjusted into different levels of coarseness through the grinder.

When the espresso shot pours it will take a certain amount of time. The ideal for this is 25-30 seconds. As the water comes down on the grinds (at about 130 pounds of force) it extracts the flavours from the grinds. However, if it is not timed right this will ruin your coffee shot.

If the shot pours too quickly then as the water runs through it does not absorb the oils or flavours in the coffee and you are left with a weak, thin espresso which tastes sour.

However, if the shot pours for too long then it is because the water sticks around for longer than it should, as it can’t get passed to the desired escape route of the coffee cup. This causes it to absorb not only the flavour but also other undesirable chemicals leaving it tasting strong and bitter.


A shot is poured

The best way to fix the extraction time is to change the grind. Water will have to force its way through a fine grind, making it take longer whereas water can rush through a coarser grind much faster. If you imagine a container of rocks and a container of sand – it takes the water a lot longer to get through the sand than the rocks as there is less space for it to get through.


It is easier for liquid to pass through larger, more coarse objects.

You can also adjust your tamping pressure as well. Tamping provides a nice flat compact bed of coffee for the water to hit and compresses the coffee grinds. A harder tamp will compact more, meaning a longer extraction time.


Tamping allows the water to hit a compact, flat surface.

Coffee extraction in its 3 stages

  1. Dark thin trickle with a strong aroma, flavour and colour that is released into the shot.
  2. The caffeine and other bitter compounds begin to be extracted from the grinds.
  3. Stream lightens in colour and then the more unpleasant, more bitter acids begin to be extracted.

So next time you get your coffee and it tastes bitter or sour – or just not quite right, you now know why! (I don’t know if that will make you feel better about it or not though).



Adenosine and Caffeine, the impostor!!

Monday morning rolls around and it’s tough. Even after two full days to laze around and rejuvenate yourself – that early morning alarm kills. So you do what you always do, press dismiss, grit your teeth and reach for that cup of joe.

Caffeine is a vital part of coffee and is one the main reasons that people drink it so often and in such large quantities. Have you ever wondered how it stops you from being sleepy and why you need to keep drinking it to feel its effect?

The human brain consists of a variety of chemical reactions to keep it and you going throughout the day. It does this through a bunch of different chemicals. These molecules need to bind to their assigned receptors in order to work. Adenosine – a neuromodulator that helps you relax and wind down- builds up in quantity throughout the day which is why you (hopefully) wake up feeling refreshed and are ready to be tucked into bed by late.


Adenosine binds with its receptors in the brain.

Caffeine however is a sneaky one. It is the same shape and size as adenosine and so when it enters the mix they compete. Caffeine binds to the same receptors which therefore blocks adenosine’s effects, stimulates your nerve cells and stops you from feeling tired.


Caffeine enters the picture and steals adenosine’s spot.

There is a catch though with long term caffeine use, your brain cottons on and creates more adenosine receptors to combat it – meaning you have to have more caffeine in order to keep the sleepiness away.


More receptors means more caffeine to keep you feeling alert.

Caffeine also has a half life of six hours inside your body which means after six hours it has half the effect that it did initially which is another reason why you need to keep having more throughout the day to keep you awake.

So now you know what is going on in your brain and why you feel so alert as you sip on your morning brew.


Wake Up!

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.

bad foam2

Nothing worse than lumpy milk.

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.