Coffee is a peculiar material. We attach such ritual to its consumption as a beverage from choice of bean supplier to how it is roasted, how finely it is ground, the method for making a drink from it and whether or not one adds milk, cream, sugar, something else, or nothing at all. And, then of course, there's "instant coffee".
Whether one is a fan of espresso (definitely no "x", although the etymology is Latin "exprimere" meaning to press so no reason for it not to have that extraneous letter), a typically larger Americano, a latte (the one which Italian waiters delight in serving as a glass of milk to unaware British tourists) or one of those decaff skinnyfrappalattamochabambiniccino things with syrup and sprinkles, there is fundamentally at the heart, the desiccated and roasted berries of the Coffea plant.
Having mentioned decaff, there was a time when the decaffeination process was carried out using a volatile organic solvent, namely benzene, now known to be a rather noxious and carcinogenic material. Today, however, it is the slightly less worrying dichloromethane or ethyl acetate that are used. Although supercritical carbon dioxide can also be used to extract the stimulant alkaloid caffeine so many crave but so many also wish to avoid.
There are lots of video clips on the internet showing you how you should make coffee to get the best taste and many of these refer to the "bloom" of coffee grounds as just-off boiling water (87 Celsius is optimal, apparently) is poured over them on a filter paper . The bloom occurs as carbon dioxide gas trapped within the grounds present from the roasting process is released by the hot water and bubbles and froths up through the mixture of wet and dry grounds. There are techniques for getting the grounds soaked before making any volume of coffee and so degassing them and avoiding the metallic soda water taste of which some coffee drinker complain. Did I mention the rituals...?
I am not convinced by these references to carbon dioxide, although I had originally thought the how-to video makers and ebullient baristas on those video clips were somehow being bamboozled by the use of the supercritical gas for decaffeination process. But, apparently not. Writing quite some time ago in the Journal of Food Engineering, Theodore Labuza of the Department of Food Science and Nutrition, at the University of Minnesota, in St Paul, and colleagues explain how carbon dioxide is generated by various reactions that occur during the roasting process. They point out that some is released during the roasting and grinding but some is trapped and only slowly released, which creates an expanding package problem for coffee sellers, but presumably not for hobbyist home roasters.
As something of an entirely amateurish domestic barista I have done various only vaguely scientific tests to see what approach would give me the nicest cup of coffee (from shop-bought, packaged roasted, ground coffee) whether I'm using a paper filter or a cafetière (that's a French press to American readers). To be honest, I'm either simply not an aficionado or none of the variations in pouring rate, press rate, water temperature, degassing bloom phase or anything else seem to make the slightest bit of difference. I strongly suspect that it is very much about the ritual. And, speaking of which it's just after 3pm, so must be time for a nice cup of tea and a slice of cake...
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".