God gives the nuts, but he does not crack them.
Brazil nuts grow near the tops of 150-foot-tall trees in hard casings similar to coconuts, but they are never imported in this form. Inside the case, 20 to 30 nuts fit together like the sections of an orange. The case and its contents can weigh anything up to 4.5kg, and individual trees can produce as many as 450kg of nuts.
Botanically the Brazil is actually a seed, rather than a nut – the nut is the coconut-sized thing. The cases fall off the trees when ripe, and are easily heavy enough to kill a person. Fatal accidents are not uncommon among collectors – they stop work at once if the wind suddenly strengthens, because this can cause a bombardment.
The Brazil trees only grow wild, not cultivated, and their pollination depends on the presence of a particular bee. The presence of the bee, in turn, depends on the presence of a particular orchid...which doesn’t grow on the Brazil trees. As a result, trees which are removed from the forest simply stop fruiting.
People who are allergic to Brazil nuts have a unique problem: it’s the only allergic reaction known to be sexually transmissible. In other words, the semen of a man who has eaten brazils can trigger an allergic response if a sexual partner of his has an allergy.
In Portuguese, Brazil nut pods are called ouricos, or 'hedgehogs'.
Anybody who has bought a bag of mixed nuts or a packet of muesli will be aware that the brazils rise to the top of the packet. It used to be assumed that this effect was trivial and easily explained: whenever you shake the pack, smaller particles fall into cavities under the larger bodies, gradually pushing the brazils to the top.
But it has now been shown that there are actually at least ten different mechanisms at work. One of them is the 'void-filling' already referred to, but there are also effects called inertia and convection – and sometimes a startling outcome called the 'Reverse Brazil Nut Effect', too. The experiment is conducted on a mechanical vibrating surface, and it turns out that the larger particles initially rise to the top, but then, if you carry on vibrating them, they sink to the bottom – i.e. you can cause the effect to go into reverse simply by waiting long enough. This outcome is only observed under certain conditions (things like the cleanliness of the container, and how full it is, seem to be key), but to be honest nobody knows in detail how the effect works.
The Brazil Nut effect is worth studying for lots of reasons: engineers don’t want mixed-up granular materials to separate out, geologists want to predict the behaviour of rubble and soil during earthquakes, and farmers have been mystified for years by the fact that flints keep coming to the surface in their fields, however many they remove.
The 'Cheerios Effect' is the tendency for small floating objects to attract one another, e.g. when breakfast cereal pieces (or bubbles in a fizzy drink) clump together or cling to the side of the container. It is caused by surface tension and buoyancy.
Not everything round is a nut, not everything long is a banana.
The Brazil nut is the only internationally traded seed crop which has to be collected from the wild.
The full Portuguese title for Brazil nuts is castanhas-do-Para, 'chestnuts from the vast ocean'.
Brazil isn't the world's biggest producer of Brazil nuts – that's Bolivia, which produces about 50% of the world’s supply.