N2O (nitrous oxide) is often used to whip cream, so one of the most common questions we are asked is, does it also contribute to the crema? One can see the confusion: crema and cream can seem quite similar in consistency (and their spelling), even through they are made from very different substances. Also, it is well known that N2O has a sweet taste, so does it also make the shot taste sweet?
These are both good questions.
The short answer is that cream and crema are not the same. In a whipped cream dispenser the N2O is mixed with the fats in the cream under pressure, and allowed to expand creating “whipped” cream. In the TWIST the N2O doesn’t ever mix with the crema, which is produced during extraction, and actually gets its airiness from the CO2 trapped in the ground coffee.
Here’s the longer answer:
Gas isn’t absorbed into the water in the 20-30 seconds it takes to make a shot. Gasses absorb much more readily into cold liquids, but the brownian motion of the molecules in a hot liquid works against this and will even eject previously absorbed gases (more on this later). For example, CO2 will absorb into a cold liquid and make it fizzy. However, heat a bottle of soda water and it will almost immediately go flat.
While CO2 absorbs into cold water, N2O absorbs into fats much more readily than water. Cream must have a minimum fat content of 28% to produce whipped cream with a dispenser. A whipped cream siphon also needs to be shaken after the N2O is inserted so that the N2O can bind with the fats in the cream. While pressurized within the bottle the N2O remains bound within the fat. However once the cream is depressurized via the nozzle and the N2O expands within the fat molecule. There is no analogy to this process in the TWIST.
In the TWIST the gas sits on top of a piston of hot water that is then pushed through the ground coffee. Pull the trigger on the TWIST and after a brief pause the espresso with crema is immediately produced from the bottom of the basket by the water. The gas meanwhile sits far above the crema and the coffee, separated by a showerscreen, one-way valve, and a column of water.
Regarding the second question, nitrous oxide is used to prevent many different products from going stale (or oxidizing). It is used to preserve numerous packaged foods including potato chips and other fried goods, cookies, boxes of cereal and even coffee beans where many large scale roasting works will inject N2O into the bags of roast beans, expelling all oxygen until the bag is opened. It is also used as an in-bottle wine preserver where any taste transformation would be highly detrimental. In the TWIST, the N2O doesn’t reach the crema or the cup, and there are no fats into which it can absorb, so it cannot contribute any sweetness to the taste. The most likely reason an extraction from the TWIST may taste less bitter than many other espressos is that it operates at a slightly lower temperature. Therefore it avoids the mistake of an “over temperature” shot that can make the espresso taste bitter.
So why does the TWIST produce so much crema?
The TWIST simulates the soft pneumatic profile of a lever-pull espresso machine. This encourages a softer shot that is produced smoothly and without vibration. This may help crema production through a smooth extraction process. However the real answer is probably related to the start of this article. If you recall, brownian motion can cause a hot liquid to expel a previously absorbed gas. The slightly lower extraction temperature of the TWIST when compared to many commercial espresso machines means that less CO2 is expelled from the crema while the shot pours into the glass, ensuring more crema sits in the glass at the end of the shot.