The world’s most expensive coffee is made from poop. And if you want a latte without the milk, you should be making it with poop, too. From bacteria, that is.
Regular lattes use milk to soften the taste of espresso and make the drink a little thicker, with creamy foam forming the latte’s classic top. But millions of people don’t or can’t drink milk, leaving them sadly without a morning latte. Except for xanthan gum.
Our friends at ChefSteps let us in on a little secret: You can use xanthan gum to make a latte without milk. How? Well, it is the purified waste of the bacterium Xanthomonas campestris, which infects leafy plants and gives them brown spots. The bacteria ferment a sugar like corn syrup and leave behind a slimy paste that gets purified into a dusty powder. In the 60 years since its discovery, the stuff has found its way into a huge array of food products, from salad dressings to yogurts to egg substitutes. (If you’re concerned about ingesting the purified waste of a plant pathogen, relax and remember that you are not a plant.)
The powder is remarkably great at thickening liquids and helping to suspend solids in place. And it works in just about any liquid: It can be hot or cold, acidic or basic, petroleum or whipped cream–or coffee. A tiny amount of xanthan gum blended in with coffee thickens the coffee up just like a latte, even with the classic foamy cap.
But xanthan gum doesn’t stop at industrial-scale biology and early-morning chemistry. It also makes for some interesting physics. Xanthan gum makes liquids like ketchup into what are called shear-thinning fluids, and it’s why ketchup only pours when you hit the bottle. Normal fluids flow whether they’re under pressure or not: No matter how angry you are at Poseidon, punching a river won’t change its flow. Shear-thinning fluids, on the other hand, only really act like liquids when they’re under some sort of pressure. Otherwise, they’re more like wobbly solids.
In an upside-down bottle, ketchup sits immobile at the bottom like a sticky solid. Striking the bottle sends a shockwave through the ketchup and switches it into momentarily acting like a thick liquid that can then flow out of the bottle. Once it’s on your plate, the ketchup is no longer under any pressure, and it returns to acting like a sticky solid–even staying there if you briefly turn your plate upside down. (Don’t try this wearing nice pants.)
So once you’re good and energized from your xanthan gum latte, try using some of the rest of the powder for physics experiments on the wonders of shear-thinning liquids.