So, we know where the bean comes from, but have you ever been curious on how it gets from that green bean in the wild to the delicious brown bean that is used for your morning coffee?

This happens by coffee roasting, which is different to the trend going round at the moment where you roast your friends. Coffee roasting is where the beans are subjected to extreme heat and heated until they turn that perfect shade of brown (which can change depending on what flavour you want to go for).


Not the type of roasting that we are talking about…

The process begins as an endothermic reaction. This just means that the reaction absorbs heat. At this stage the beans are dried slowly until they begin to smell – this will normally smell like popcorn or toast. People from Dunedin will be very familiar with this smell, as the Greggs factory wafts its burnt toast smell across town – especially bad on my side of uni (apparently there have even been concerned people in the department who think a fire has started).


Coffee Roasting

After this smell begins to occur, the next step known as ‘the first crack’ happens at about 205°C. During this stage, the bean become a lighter brown colour, double in size (due to carbon dioxide loss) but loses about 5% of its weight.

The beans lose their green colour through this process due to the breakdown in their chlorophyll and well as the Maillard reaction. This is a chemical reaction between amino acids and sugars which end up producing flavour compounds and melanoidins (which also contribute to that lovely brown colour).

Anyway, back to the roasting. The temperature is then increased to about 220°C. The bean loses more of its weight – about 13% and the colour changes to a darker colour.

This process is called pyrolysis. This is the decomposition of organic material and is basically what happens to all your food when you cook it and is also responsible for the colour of the roasted bean.


Different coffee roasts – Taken by Jessica Spengler

The next step is exothermic (the heat is released) and then the second crack occurs. The bean gets darker still and the temperature gets cranked up to bout 225-230°C. This is when the beans get their oily outer layer.

Depending on how long the roasters leave the bean in during this process will alter the type of roast they will get in the end. The degree of the roast will change the flavours that come through from the bean.

There you go, another week. #SCIENCED

Make sure you are back on Sunday for more coffee science!!

Photos taken from:


Coffee without the hit

A week or to ago I explained the effects that caffeine has on your brain and body. However, there are certain people who can not handle the effects of caffeine and instead drink coffee for the pure delicious taste rather than its fantastic ability to get you through your day.

But how exactly do you get the caffeine out of the coffee bean?

Prepare to science!!

The decaffeination process starts off the same way no matter which method you use, with the bean in its green, non-roasted state.

There are three main methods of decaffeination.

The swiss water method

Basically this method submerges the beans in very hot water – think of a spa but for coffee – which washes off the caffeine. The beans are then put through an activated charcoal filter. This filter stops the caffeine particles from moving through but the smaller particles like the oils and flavours are free to flow. These old beans are then thrown away and this flavour rich water (green coffee extract) is used to wash away the caffeine on new beans while maintaining the flavour. This is because there is already the flavour particles in the water so the ones inside the beans have no where to go – it’s too crowded out there for them so they just to stay at home.  All together this takes about 8-10 hours.

The direct solvent method

This method requires the beans to be steamed for 30 minutes which helps to open their pores (again, sounds like a lovely day at the spa). Then to remove the caffeine the beans are then rinsed with dichloromethane or ethyl acetate for around 10 hours. The solvent is then removed and the beans are steamed once again to get rid of any of the leftover solvent.


A green bean enjoying the steaming process

Some people are concerned about the use of solvent in their coffee beans – however there is only one part per million of the actual solvent used and it is also very unlikely to survive the roasting process.

The supercritical carbon dioxide method 

In this process the C02 (carbon dioxide) works to remove the caffeine. The green beans are soaked and then subjected to high pressure C02. The gas works as a solvent (like above) and removes the larger caffeine particles while leaving the smaller molecules behind. The caffeine is later removed from the C02 through a carbon filter. The gas can then be reused. This is a cheaper way of doing things, and less risky than the solvent method.

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SUPERcritical carbon dioxide

So there are the three main ways that the coffee beans can be decaffeinated. However, if you can handle it I would recommend caffeinated coffee, as there is less damage done to the flavours. Also, the decaffeination process changes the beans to a brown colour, which makes it more difficult for the roasters to know when they are done.

Hope you enjoyed learning about the decaffeination process – see on Friday for the next post!!

Cool Beans!

Hey everybody, hope you are all looking forward to your weekend ahead!

This week I thought we could talk about the science behind the actual coffee beans – it’s easy to forget these days with your instant coffee and self-foaming drinks that once that your coffee was a little green bean thousands of miles away.


The coffee plant (a tropical evergreen shrub, genus Coffea) started off  being grown in Africa and is now mainly grown in The Tropics of Cancer and Capricorn. If like me, you have no idea where that is then this picture should help.

There are two main types of coffee beans that are used in commercial drinks and these are the Arabica and Robusta beans.

The Arabica plant has dark green leaves and is quite large. It takes around 7-9 months to be able to pick the cherries (where the beans live), which contain two seeds on average.


Arabica Plant

In contrast the Robusta plant is a small tree which grows to about 10 metres. It takes the beans around 10-11 months to mature in this species. The beans are also more oval and smaller than Arabica.


Robusta Plant

The overall trend for these beans is that the robusta is far more outgoing than the Arabica. Robusta can handle hotter temperatures (24-30°C vs 15-24°C) and are easier to grow and maintain. One reason for this is the level of caffeine you find inside.

The Robusta beans have about double the amount of caffeine. This is thought to be a safety mechanism as the bitter flavour deters insects from biting into their delicious flesh. This is why Arabica does better at higher altitudes as there are less pesky bugs hanging out there.

There is also an effect on the flavour as well.

Here are some quick-fire differences between the beans.



  • Stronger, harsher taste.
  • Twice as much caffeine but are a lower quality.
  • If good quality though they are good in espressos for their crema and flavour.
  • Easier to grow – less likely to get attacked by pests or the weather.
  • Produce more beans.

Although Arabica is the preferred bean to have in your coffee, a lot of places will put Robusta beans into their blends to reduce the cost, as these beans are way cheaper to produce.

Hope you enjoyed learning about the different types of beans in your coffee – now you can check what type you are having when you buy.

Have a good weekend and see you on Sunday!



Photos sourced from: 



The coffee and the landfill (a classic romance)

Sunday mornings. They can be hectic – rushing around trying to get your last-minute errands done before the new week starts, or they can be chill and relaxing – the calm before the weekly chaos begins again. However, you spend it I think we can agree that a coffee in hand makes it a more pleasant experience.

Have you ever thought of how much your Sunday coffee is impacting the environment though? To the outside eye your takeaway coffee cup just looks a paper outside and plastic lid – however there are more sinister things lurking beneath the surface. The inner lining of the cup is made of polyethylene  plastic which can’t be recycled in New Zealand and so means every single take away cup you ever have had is on a landfill, as it becomes too costly to remove the plastic away from the paper.


An alternative to polyethylene lined cups are reusable cups.

Five coffees a week results in 14kg of waste a year.

There is 1 million disposable cups put in landfill every minute


Your sad, abandoned coffee cup.

There is now a move to make your takeaway cups compostable  instead. Most of the cup will be made of plant material instead. For example ecoware uses a plastic that is made from sugarcane or corn starch. These plastics (polylactic acid or polylactide) are not only biodegradable but also come from a renewable source. However, these cups can still not be recycled.

Compostable and and biodegradable mean different things too, so be careful and keep this in mind when companies market their products.

Compostable: Able to ‘disintegrate into natural elements in a compost environment, leaving no toxicity in the soil.’

Biodegradable: Can be broken down quickly by microbes. It has also seen that plastics in landfills release methane gas which is contributing to global warming (which is 100% true, no matter what the FAKE NEWS says.)

It can be hard to guarantee that the café you visit has these compostable cups though, so if you want to take matters into your own hands you can always buy a reusable cup.

I recently purchased a cup off http://nz.keepcup.com/ and love it!! The site allows you to pick your own colour scheme as well as picking from a range of types and colours.  These cups are also made of fully recyclable materials so can be shipped off at the end of its life (which is apparently 3 years +).  During these 3 years, you alone would have contributed 2.7 kgs of plastic to the landfill. The only downside of these is carrying them around – but are fine if you know in advance you are getting a drink.


Baristas are always happy to use other cups (it makes less dishes for them) 👍

Another alternative is always to take a break and sit down and enjoy a nice ol’ fashioned have here coffee.

Happy drinking friends! Hope you are now enlightened to the effects of your weekly coffee cups. 😀





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.