For my mum’s birthday I got her a coffee machine with a difference- a coffee machine on steroids if you will. At £1600 it’s not for your everyday PhD student, but this is a special birthday (she’s 21 !) and I love her more than I love fancy handbags. The coffee machine is a cuboid of stainless steel glory: it’s classier than anything in our kitchen (we’ve already had two viewings from passing neighbours) and almost certainly makes better coffee than the high street vendors. Not only do you get to choose the coarse-ness of your grind (that’s totally a thing) but you get a free training session with a barista- A BARISTA! IN YOUR OWN HOME!
Well, actually, on the morning of the aforesaid training I was pretty annoyed about it all really. I was under the impression I was much too important to have a coffee lesson and that I hadn’t made quite enough graphs that day. Boy was I wrong. Josh, the pro-barista of Coffee Classic LTD, who provide the ‘white gloves’ service is everyone’s favourite grinder. He’s fitted two of these machines in ‘Heston’s properties’ and has more than one himself (‘incase one breaks’). He doesn’t endorse any other domestic appliance.
The perfect coffee has more science in it than a solar panel. And after making your perfect espresso; the discipline of milk texturing is like postgraduate study. To make the perfect coffee; everything has to be hot- the ‘porterfilter’, where you hold your ground (not too fine) tamped (not too squished) beans, the top of the cup that you hold to your mouth, the water pre- and post-infusing. The ‘crema’ has to be bold. The texture has to be like runny honey.
The milk can’t be too hot. The proteins in the milk have to be moving around pretty slowly, so that when the high-pressure jet of steam goes in the bubbles can effectively bind to the protein and froth the milk. It doesn’t matter if the milk is full-strength, low-fat or semi-skimmed- there’s still protein and the protein can still bind to the bubbles. The perfect ‘frother’ doesn’t waggle their hand about frantically, but gradually nudges the head of the jet hits the surface of the milk. The temperature of the milk is optimum when it’s between 55 – 65 °C. You create circular vortices in the milk: pointing the ‘wand’ diagonally away from the ‘edge’ of the jug, and keeping the wand just below the surface of the fluid. The circular vortex moves the big bubbles around the jug, turning them in to tiny velvety little balls of foam. After the milk reaches 38-40 °C you can’t keep adding volume, and you start to steam the milk itself. Finding the right position to achieve good increases in volume (think Russel Brand’s hair circa 2007) and minimal milk splash is tricky, but after you can pour crazy thick foamed milk. A brief tap on the counter will pop and rogue huge bubbles, and the milk can keep warm for 5 mins whilst you perfect your espresso.
I’m hoping we can arrange a proper coffee X science session at Imperial soon… Until then, I’ll just keep jittering around my office and staying up all night googling the science of the perfect espresso….