In 2003, the European Union imposed strict regulations on the import of nuts from Brazil harvested in Brazil in shell, since the shells are considered to contain dangerous levels of aflatoxins, a possible cause of liver cancer.
In July 2003, it was very difficult to find unshelled Brazil nutsin the UK. The reason is that certain molds, called Aspergillus flavus and Aspergillus parasiticus, can form in shipments of nuts (molds can also form in peanuts and sweet corn). In order to be sold in shell, walnuts must be tested to comply with new EU rules, and supermarkets cannot cover the cost of testing and continue to sell nuts at a price that they believe consumers will be able to continue to pay.
You can still buy shelled Brazil nuts in the UK, as the cost of trying shelled walnuts is minimal. Because the cultivation of trees on plantations is still in a very tentative stage, most of Brazil's nuts are still harvested in nature. Regardless of the method you use, you'll still need a serious nutcracker, hammer, or mallet to open them. The Food Standards Agency said that aflatoxins were formed by certain molds in foods, in particular nuts grown in warm, humid conditions.
Progress is being made by planting other types of flowering plants around and between Brazil's walnut trees to keep bees in the general area throughout the year. Once out of the pod and hidden somewhere by the agouti (and forgotten by the aguti), the nut shell can take a year to open on its own and finally allow the nut (or “seed”) it contains to sprout and grow. The size of the pods varies from that of a grapefruit to that of a coconut, weighing up to 5 pounds (2 kg). Tesco, Sainsbury's, Asda and WM Morrison do not stock nuts with shells, but continue to offer packaged grains.
Bees don't live near trees, because trees only bloom, of course, for a small period each year, and there's nothing that interests them in Brazil's walnut forests the rest of the year. The cost of this operation has forced most retailers to switch to introducing only grains, the edible part of the nut. The European Commission has classified Brazil nuts in shells as a health risk, after traces of a toxin related to liver cancer were found in the shells. While walnuts can still be imported in shell, the EU ruling means that they must be inspected and tested for aflatoxins.