Skip to 0 minutes and 6 seconds Coffee beans are the green seeds of a cherry that when roasted, changes colour from green to brown. This change of colour is caused by the Maillard Reaction, which is commonly called browning. The brown colour is made up largely of compounds called melanoidins, which are high molecular weight polymers formed when sugars and amino acids combine. This is an extremely complicated process and not much is known about the detailed structures of the melanoidins that are formed. One thing that we do know about the melanoidins, is that these brown-coloured pigments, together with other coloured compounds in coffee, can act as stains.
Skip to 0 minutes and 44 seconds Dunking paper in coffee can be used to give it an antique look, while painting plywood with a cup of coffee can darken it. In fashion, coffee has even been used to dye fabric, such as t-shirts and jeans for a distressed look. You may also have seen the scientific interest in coffee rings - the phenomenon to explain the ring-shaped stain of particles leftover after coffee drops evaporate is important in, for example, inkjet printing. Coffee rings are also important in the art world - Malaysian artist Hong Yi took the internet by storm with a stunning painting of singer Jay Chou made simply with thousands of coffee stains, using a coffee cup.
Skip to 1 minute and 24 seconds She had to get the coffee mixture just perfect, as the ring stains were permanent the moment they touched the canvas and she spent around 12 hours working on this incredible piece. Now it is your turn to utilise the staining power of coffee to positive effect! Use a coffee cup, brush and/or anything else to paint the structure of an organic compound found in coffee. Perhaps methylpropanal, caffeine or a more complicated structure, such as cinnamic acid. You have over 1000 compounds to pick from! It could be an abstract design, or more detailed, showing individual atoms. You may want to experiment with different coffees, of different strengths. Now is the time to make your mark!
Skip to 2 minutes and 5 seconds Don’t forget to post a photo of your creation, including why you picked the structure you did, and the coffee you used.
Art with coffee rings
So, rather than coffee staining our teeth, or coffee table, let’s use this staining power creatively to make a ‘molecular’ work of art.
Hints and tips for coffee art
1. Make sure that the coffee is very, very strong. We used approximately three times the amount of filter coffee needed for a standard cup and around a third of the amount of water – it needs to be very concentrated to colour the paper.
2. To make a background like ours (to look like parchment paper) you can use tea or coffee. If using tea, soak the tea bag in cold water for a minute or two and then rub the soaked tea bag directly onto the paper (try not to get it too wet), before placing the tea soaked paper into a preheated oven at about 80 °C until it is dry. Keep an eye on it because it will not take very long to dry. For coffee, brush a coat onto the paper and then put it into the oven at about 80 °C until it dries. Repeat if the colour is not as dark as you'd like.
3. After the background is complete, ensure you put dots to mark the places of atoms for your molecule. This is an important step, because drawing the molecule freehand, without any guide marks, will most likely result in you running out of space.
4. Using a thin paintbrush dipped in coffee, carefully trace out the shape of the molecule (once only). It is tempting to continue to go over it multiple times quickly to try and get a more defined figure, but it is important to allow the first coat to dry before you do the second, if you want a well-defined molecule. Putting more coats on top of a wet coat will just result in the coffee spreading to the surrounding paper and you will get a more abstract looking molecule. For best results, put the paper back into the oven at about 80 °C between coats, allowing for a quick dry.
5. In total, your molecule will probably require six to seven coats to look well-defined and, using the oven method, you should have a perfect coffee-coloured compound in no time. If you'd like to burn the edges to make it look more ancient, you can use a match or a lighter, holding it to the edges of the paper and blowing out the flame once you have got the desired look. Do each little piece slowly, otherwise you risk burning too much and losing some of your molecule.
Remember to upload your work onto our open Padlet (we have included some examples from previous years to help inspire you) and/or on Twitter or Instagram hashtag #FLchemistry, we are eager to see what you can create!
While you are creating your masterpiece, you might like to reflect on some interesting articles about coffee.
Coffee can be good for you
A study has found that if the coffee beans have been highly roasted then the drink is less beneficial for your health. Concentrations of chlorogenic acid were found to be reduced on roasting and so the potential positive effects of this polyphenol (such as improving the function of the circulatory system and reducing the risk of developing high blood pressure) are diminished.
Also, in 2017, a large review of studies showed that moderate coffee drinking is safe, and 3-4 cups a day may have some health benefits. This included finding a lower risk of liver disease and some cancers in coffee drinkers, and a lower risk of dying from stroke. However, the researchers could not prove it was due to coffee, so experts advise that you should not start drinking coffee for health reasons.
When is the best time to drink coffee?
Interestingly, the time at which we drink our coffee may alter its effect. If we consume coffee during times of peak cortisol (a hormone that is produced in our bodies to make us feel more awake and alert) production, research has shown that the effect of the caffeine will be greatly diminished during that time and our bodies will build up a greater tolerance to the effects of caffeine. For many people the optimal times for consuming caffeine appear to fall somewhere around 9.30-11.30 am and 1.30-5.00 pm. For the coffee-drinkers, why not challenge yourself to limit your caffeine intake to the prescribed time slots over the next few days and tell us what you loved and hated about it, and whether you noticed any difference?
Does coffee or tea stain teeth more?
Our tooth enamel is prone to staining as it contains microscopic pits and ridges that can hold particles of food and drink. Pigments from dark-coloured drinks such as coffee and tea can become embedded in the cracks and ridges causing yellowing stains of our teeth.
A dentist recently claimed that black tea can have more of a detrimental effect than coffee, on staining our teeth. Many assume coffee has a greater staining power because it is darker in colour than tea, but looks can be deceptive. The high levels of tannins (a family of compounds containing phenolic groups) in tea, including theaflavins and thearubigins, are believed to be responsible for the greater staining. Tannins from plants, particularly oak bark, were once used in the process of tanning leather (they preserve the animal skin by binding to collagen proteins, making the skins stronger, stiffer, waterproof and resistant to bacterial attack).
Comparing the staining properties of coffee versus tea makes a really interesting science project!
Watching coffee dry
You may find this (microscopic) video of the coffee ring effect interesting - watch as spherical particles get swept to the edges.
This is an additional video, hosted on YouTube.
Finally, add a drop of whiskey
On drying, drops of whiskey have been shown to provide unique patterns that might provide a tool for authorities investigating counterfeited products. Research showed that when American whiskey was diluted with water down to about 20–30% alcohol content, on evaporation, the droplets began to leave web-like patterns on the glass. The patterns arise because hydrophobic compounds within the whiskey aggregate when the water is added – each whiskey has its own flavour profile, made up of thousands of different compounds, including different hydrophobic compounds, so different brands gave unique motifs.
© University of York