With so much competition out there in the Cafe market, a bad coffee experience repeated can be devastating for the business. The good news is that the quality of the coffee you serve in your shop or drink at home is completely within your control.
Things you can control
- coarseness of the grind
- temperature of the extraction
- extraction time
- the all-important coffee-to-water ratio.
- The person making it!
Things you can't control
- The quality of coffee bean itself
I've experienced this more times that I can remember where I have gone to 2 different shops and getting 2 different tasting coffees when the shops were using the same beans. This is a result of the 'Things you can control' being different from shop to shop and machine to machine.
The coarseness of the grind and the extraction time are inextricably linked. The finer a coffee is ground, the more surface area there is. Conversely, the larger the grind, the smaller the surface area.
Let’s consider the two ends of the extreme. If we grind coffee as fine as talcum powder we have maximised the surface area available for extraction. Therefore, we can very quickly extract the target compounds – but perhaps too quickly for some people’s tastes.
Turkish coffee is very finely ground and boiled. This produces a coffee which is very strong and bitter and because of the fineness of the grind often contains a lot of suspended solids (muddy). The finely ground material may block filters too, causing the extraction to go on for too long – or not allow the water to pass through at all.
At the other end of the spectrum, let’s consider whole coffee beans. Of course, given enough time, we can extract unground coffee. This is quite wasteful of the coffee beans because the hot water may not penetrate all the way to the interior of the bean, so we throw away unextracted material.
Obviously, the optimum grind (coarseness) is somewhere between these two extremes, where we match the residence time of the hot water (flow rate) across the ground coffee beans with our ideal caffeine/ volatile oil/ organic acid ratio.
If you get a cup of coffee produced from a quality bean but it is too weak and insipid, the coffee may have been ground too coarsely. If the coffee is unacceptably bitter, perhaps the grind is too fine, with too-high levels of organic acids being extracted.
Let’s hold all of our variables except temperature constant and see what happens. As with our coarseness experiment let’s consider the two ends of the extremes.
Temperature strongly influences solubility and rates of extraction. Yes, you can extract coffee with ice water. Cold Brew Coffee – ground beans are placed in cold water and allowed to “brew” in the fridge for up to a day
The solubility of caffeine is slightly affected by temperature and the solubility of the organic acids is heavily affected by temperature. We would expect that a coffee brewed using this method would be lower in caffeine and much lower in bitterness than a coffee brewed using hot water.
Using boiling water everything gets extracted much quicker and the margin for error becomes much smaller if we try to limit bitter organic acid content. There are also the oils to consider which are volatile. If we boil coffee, our flavour and aroma compounds get carried away in the steam. This can produce a coffee that is weak in taste, yet high in caffeine and organic acids.
In part 2 we will continue to go further into what makes the perfect cup of coffee