Is it risky to eat mussels that do not open? D. Freund

Apparently in the first edition of Jane Grigson's Fish Book in 1973, Jane Grigson stated, "Throw away any mussels that refuse to open". I cannot corroborate this as I can't find a 1973 edition. This line does not appear in my 1994 edition. Anyway, this piece of information stuck. It is bollocks. What you should do with mussels is throw away those with broken shells or those with shells agape that don't close when tapped. They are probably dead. Shells that are really heavy may be filled with sand, unlikely with modern farmed mussels, and should be opened separately before cooking. Mussels that do not open when cooked can be prised open with a knife. Carefully. Mussels with orange flesh are female. Those with pale, creamy flesh are male. Those with green shells are from New Zealand, and they are cooked and frozen before they arrive here. Grigson's book does give an excellent recipe for eclade de moules, a mussel barbecue from the Ile d'Oleron in France in which mussels are laid out on a wet plank and covered in pine needles that are set alight to cook the shellfish.

Why do we call the peppery salad leaves "rocket"? P. Lane

A late friend once wrote a poem in which she postulated that you could plant a brassica on the Nullarbor Plain and a bloody cabbage moth would somehow find it. Cabbage moths love brassicas. Always have. The Romans noted this. They even identified a plant on which the cabbage moth eggs were laid. Caterpillar in Latin is eruca, so they named the plant eruca as well. Caterpillar plant. As the plant went over the Italian alps it became rocchetta. When it got to France it morphed into roquette. In England, this was anglicised to rocket. The Americans, as we are all too aware, have a different lexicon. They call it arugula. This came to America through another dialect, a part of Italy where the plant is known as rucola.

I have brought home two bags from the bulk foods shop. One is cream of tartar, the other is baking powder. How can I tell them apart now that they have been mixed up? L. Nelson

One is acidic, the other alkaline. Take a teaspoon of each and place them on separate plates. Add a teaspoon of vinegar to each. Vinegar is acidic and will react with the alkaline powder, the baking powder (sodium bicarbonate), by fizzing up. Cream of tartar (potassium bitartrate), being acidic, won't react. A word of warning: do be careful mixing up your white powders. It can lead to all sorts of embarrassing situations.

Correspondence

Recently a reader complained about a fishy smell to her eggs. We pointed the finger at fatty acids in vegetable oils. G. Buzza weighed in, writing "I think you will find that the real culprit is trimethylamine that gives the eggs the fishy smell. This is likely caused by feeding the hens canola meal (aka rapeseed meal), which contains sinapine. The sinapine is converted to trimethylamine by some breeds of chooks – which is sometimes correlated with the colour of the eggs." And, according to the research papers, trimethylamine smells like fish.

Send your vexing culinary conundrums to brainfood@richardcornish.com.au or tweet to @realbrainfood.