{"id":3101,"date":"2016-08-10T07:00:34","date_gmt":"2016-08-10T07:00:34","guid":{"rendered":"http:\/\/www.beanthinking.org\/?p=3101"},"modified":"2016-08-10T07:05:43","modified_gmt":"2016-08-10T07:05:43","slug":"super-cold-brew","status":"publish","type":"post","link":"https:\/\/www.beanthinking.org\/?p=3101","title":{"rendered":"Super cold brew"},"content":{"rendered":"
\"Cold<\/a>
Cold brew coffee served with ice. Image from pixabay.com<\/figcaption><\/figure>\n

How cold do you drink your cold brew? Poured over ice? As an experimental physicist who works with liquid nitrogen (& helium), I was initially quite intrigued to learn of nitro cold brew coffee. Could it be coffee that somehow uses liquid nitrogen to fast-cool it, what would that do to the taste? You would expect liquid nitrogen (at -196\u00baC) to\u00a0rapidly cool the coffee below its freezing point, after all, it is how Heston Blumenthal makes ice cream.<\/span><\/a>\u00a0To make a drink-able cold-brew with liquid nitrogen would require great skill, especially given the potential health risks<\/span><\/a>. It would be another situation where you may well ask yourself, “what’s the point?”<\/p>\n

However, it turned out that the reality was far more mundane<\/span><\/a>, gaseous nitrogen is passed through cold brew coffee<\/span><\/a> to create a drink with a silky mouthfeel. A smooth drink that comes straight from the tap just like stout. Such a drink is going to behave as an ordinary liquid and chilled only to the point that it is kept in the vat. The novelty would presumably come from the mouthfeel introduced by the many tiny bubbles distributed through the drink. Just as with water, if you cooled the nitro-brew below its freezing point it would solidify and form coffee cubes. No real difference to get excited about. But what if there was a very different sort of liquid, a “super liquid”, that didn’t behave like water, coffee or even liquid nitrogen but one that could leak through solid cups?<\/p>\n

Superfluid helium is such a liquid. Like water, oil or even liquid nitrogen, when you cool helium (the same gas that is in party balloons)\u2217, it becomes an ordinary (but very cold) liquid at -269\u00baC. But unlike those liquids, when you cool it further, below -271\u00baC, it does something very odd indeed. It becomes a superfluid in which the liquid moves with zero friction or equivalently,\u00a0zero viscosity<\/span><\/a> (honey is very viscous, water is very much less so). \u00a0And it is because of these properties that it can do some astonishing things such as stream through cracks in containers that were thought impermeable (see the video at 0:52m), or even climb the walls of the container it is in (1:13m)!<\/p>\n