Skip to 0 minutes and 6 seconds In Britain it is estimated that a staggering 165 million cups of tea, and 70 million cups of coffee, are drunk each day. Back in 1946 George Orwell said that there are 11 rules for perfect tea making, rules from which nobody should dare depart. To mark the 100th anniversary of Orwell’s birth, the Royal Society of Chemistry (RSC) commissioned research, concluding that Orwell’s rules were quite wrong - for example, it argued against adding cold milk to hot tea as this makes denaturation, or degradation, of the proteins in the milk more likely. But what is the best way to make a perfect cup of tea?
Skip to 0 minutes and 46 seconds This is partly related to the steeping, or soaking, time - how long the hot water is allowed to be in contact with the tealeaf. Leaving a tea bag in longer, in boiling water, will clearly make a stronger cup of tea. Interestingly, the International Organisation for Standardisation has specified a period of six minutes for brewing tea. It is not intended to produce a good cup of tea, but it is designed to produce a consistent one for taste testing. So, adding hot water to the tea bag allows the flavoursome compounds to become extracted into your pot, or cup, or tea. But, not all of the compounds are extracted at the same time, so different flavours ‘escape’ the leaf at different times.
Skip to 1 minute and 27 seconds This activity is designed to investigate the different extraction rates of the aroma and flavour compounds in tea and coffee. First set out four or five cups. For tea, take a tea bag in a hand-held sieve and slowly pour hot water onto the bag and let water drip into the first cup, then move the bag over the next cup and so on, to give four or five fractions. For coffee, use the drip-brewing filtered coffee method - this is where hot water is poured over roasted ground coffee beans contained within a cone of filter paper. Drip filter ground coffee into each cup in turn.
Skip to 2 minutes and 4 seconds Now smell and taste each fraction in turn - for coffee, does the first fraction taste acidic or sour? Do you notice a change in the aroma as you move from cup to cup? You might like to try using hot water at different temperatures - use a thermometer, record the temperature, and see if changing the temperature affects the extraction process, by altering the flavour and aroma of the different fractions. Before finishing it is worth combining all four or five fractions and taste how they complement one another in the combined brew. At each stage of the extraction, describe the aroma and flavour, and record your findings.
Skip to 2 minutes and 39 seconds Post your results - don’t forget to identify the specific tea or coffee you used, and let’s see what information we can extract!
Serial extraction of coffee and tea
The following ingredients will be required:
- Ground coffee
- Boiling water
The following items will be required:
- Measuring spoons
- Measuring jug
- Five cups
- Filter paper
Ensure that you read through all of the instructions before beginning the experiment to ensure that you understand exactly what will happen at each step.
Measure out two tablespoons of coffee into some filter paper and position the full filter paper into the bottom of the first cup, as shown in the figure below. Then place the four other cups in a row alongside the first, for the following fractions.
Boil the kettle and measure out 500 mL of boiling water into a measuring jug. You are going to need ~100 mL of water for each cup that you have. Not all the water will pass through the filter paper in the time allowed for the extractions, but it's useful to have extra water in case you start to run out.
Set the timer to 30 seconds. As you start to pour the boiling water, slowly into the first cup, begin the timer. Stop pouring the water when the filter paper looks about half full – but keep topping it up, as it gets low. If you fill the filter paper up too much, you risk spilling the water as you try to transfer it between cups, which will ruin the experiment.
After the 30 seconds have passed, transfer the filter paper to the next cup, starting the timer again (for another 30 seconds) and ensuring to top up the water level in the filter paper when it looks like it is getting low. Continue until all the cups are full (look out for colour differences between the fractions).
Now you should taste each fraction of your coffee – remembering to leave enough to combine them at the end, so you can taste a complete cup of coffee – and you should record what each fraction tastes like. We have provided a table below of our results and a blank one for you to fill in. Make sure to take note of what kind of coffee you used.
Type of coffee: LavAzza Qualita Rossa Filter Coffee
|Fraction number||Time of extraction (seconds)||Taste description|
|1||0 to 30||slightly acidic|
|2||30 to 60||very acidic, slightly sour|
|3||60 to 90||strong flavour, very heavy|
|4||90 to 120||bitter|
|5||120 to 150||very weak coffee flavour|
After completing the table, mix each of your fractions into one cup and taste them all together. What does the resultant coffee mixture taste like?
For the tea drinkers, a further ‘tea extraction experiment’, blank results tables and the risk assessment can be located in the additional PDFs found at the bottom of the section. Remember to upload your results to our open Padlet (we have included some examples from a previous course to help inspire you) and/or on Twitter or Instagram hashtag #FLchemistry – alternatively, you might like to explain your results using the comments section below – we are eager to see what you have been able to come up with!
There will be a prize for the best photo/description posted on our on Padlet site and/or on Twitter or Instagram by 9am on Monday 20 July (week 4). The prize will be given to the person whose photo/description, in the opinion of Andy, is the most striking, detailed, informative and well presented. We will advertise the name of the winner in week 4 (in the Comments below) who will be sent a paperback copy of Keynotes in Organic Chemistry and a Chemistry@York fidget spinner. (This competition is being run by Andy / University of York and is not affiliated with FutureLearn and any personal details submitted by the learner will only be used for the purpose of sending the prize.)
We hope to get lots of interaction and that your extraction gives you satisfaction, and a positive reaction! Why not give it a go?
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