This calculator works out how much ground coffee you should use when brewing, either with a cafetiere or drip coffee maker.
How to use
Enter the volume of water, with which you are brewing with, in the first box (i.e. how much coffee you want to make). Then select which unit of measurement you have used (either millilitres of fluid ounces). Press the 'calculate' button and the weight of ground coffee you will need appears in the second box. If you do not own accurate scales: one tablespoon holds approximately 5 grams of coffee; and a coffee scoop holds approximately 7 grams.
How the Calculator Works
The calculator is based on the brewing ration: 60 grams of coffee to 1 litre of water. Using the correct amount of coffee to water is the key to a good extraction. All the desirable flavours pass into the cup while the undesirable ones are left behind.
Different flavours found in coffee beans have different levels of solubility. Some flavours dissolve quickly into the cup, whereas others take much longer. Ted Lingle identified four main groups of solubility, which we have adapted below:
If you imagine that these different groups of flavour form an orderly and patient queue, waiting to be dissolved by water. Only after the previous group has been fully dissolved can the next group start. So the first flavours that enter the cup are 'delicate', then 'mid-tone', followed by 'sweet' and finally 'bitter'.
The bitter group is full of undesirable flavours and unsurprisingly leaves a overwhelming taste of bitterness in the cup. Hence, bitter tasting coffee is called over-extracted. Surprisingly enough, the cause of over-extraction is often using too little coffee. The higher the ratio of water to coffee, the quicker the first three groups of flavours dissolve. This then leaves an opportunity for the bitter flavours to dissolve to. By using more coffee you effectively minimise the opportunity the bitter group has to dissolve, as it is now stuck at the back of a longer queue.
You might think that this is too much ground coffee and that it is going to taste too strong. If this is a concern, still use the calculator, but brew a smaller volume of coffee. Then once you have finished brewing, simply top up your cup with more hot water. By not adding more water until after the brewing process, you keep the correct coffee to water ratio and therefore avoid over-extraction.
Of course the opposite of over-extracted is under-extracted. This is when only the first two groups of flavours have dissolved. Under-extracted coffee lacks depth of flavour and can taste sour or astringent as it lacks sweet flavours. Under-extraction is often caused by too much coffee.
Research behind the Brew Ratio
The brew ratio was arrived upon from a taste study conducted by the National Coffee Organisation (USA) in the 1950s. Over the years, other institutes: such as the Speciality Coffee Association of Europe, have conducted similar studies which have all agreed with this ratio.
The original study by the National Coffee Organisation investigated what happens during the brewing process. They conducted a series of consumer preference studies, to discover how to brew the best tasting coffee. The studies found that the majority of consumers favoured coffee within a certain level of extraction (between 18-22%). From these results they were then able to develop this brewing ratio.