Via Winchell Chung​, important matters!

Via Winchell Chung​, important matters!

Originally shared by Don Pettit

The crema; it does not float to the top of your espresso when in weightlessness. The signature trait of an espresso is the layer of crema. It consists of stabilized foam created from a complex array of organic surfactants liberated in the brewing process. Carbon dioxide, liberated from the coffee grounds when subjected to hot water, fills the bubbles, which is perhaps one acceptable use for this greenhouse gas. The brewing takes place under pressure, up to 8 atmospheres (over 100 PSI), and when released into your cup, the sudden drop in pressure coupled with all the organic complexities creates this wonderful foam. The crema has a lower density than coffee so it floats on the surface as a cohesive mass. The bubbles slowly pop, releasing olfactory essence that greets our nose and contributes to the whole culinary effect.

In space the olfactory sensations will be different. If sipped through a straw from a bag (the normal engineered way to drink in space), none of the aromatics will find passage to your nose and the coffee will taste, well, like coffee would if you had a clothespin on your nose. If sipped from the space cup, your nose will find its way below the curvilinear entrance where the aromatics can tickle your olfactory sensation while sipping this orbital delight.

So what will happen to the fate of the crema in weightlessness? Before Samantha Cristoforetti did the experiment, the answer seemed obvious: the crema will not form a top layer but instead will remain mixed, forming a turbid brew of coffee and bubbles. Quite unexpectedly, something new was observed. A spontaneous structure formed throughout the espresso-crema mixture where larger bubbles formed centers surrounded by circular clouds of finer ones. When I saw the downlinked photo I couldn’t help but think of a Hubble photo of a nebular cloud forming solar systems, all in your space cup of coffee.

photo captions:
Crema on Earth (left) forms a floating foam layer consisting of mostly fine bubbles with a few larger ones. Notice how capillary forces driven by the two-angled walls are attempting to lift the crema “up”. Crema in space (right) remains suspended within the bulk espresso forming a turbid suspension that climbs the angled walls via capillary forces parking itself at the winged-lip ready to be sipped. An unexpected structure formed where larger bubbles become surrounded by a circular cloud of finer ones.


  1. Ooh, and that is the zero gee cup. Heston was playing with one to see if it could be used for tea in his latest shenanigans.


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