Dear Xanthe: How can I keep the colour on purple beans? 

Our expert is on hand to handle your culinary conundrums. Email your questions to [email protected]

Purple reign: These beans lose their colour all too soon, but there are ways to prolong it
Purple reign: These beans lose their colour all too soon, but there are ways to prolong it Credit: Getty images

Dear Xanthe 

How do you keep the colour on purple beans?

Sophie, Lincolnshire

Dear Sophie 

It’s so frustrating: long purple beans, their violet skins hiding bright-green innards, look enticingly exotic in the greengrocer’s but as soon as they are plunged into boiling water the maroon washes away, leaving you with blue water and boring green beans.

They’ll still taste great, but you may as well have bought green ones in the first place. That colour is water-soluble, so if you want to maintain it you need to keep the beans away from hot water or steam.

Try tossing them in olive oil and cooking them on a griddle until patched with brown and tender. You’ll still lose a bit of the colour, but as it is from anthocyanin, the same compound that gives red cabbage its burgundy hue, acid will turn the purple to pink, so a little lemon juice will brighten the colour that remains. Season well and tip over some sliced garlic, cooked in olive oil until just turning gold.

Dear Xanthe 

What exactly is a pinch of salt?

Sevda, via Twitter

Dear Sevda 

A pinch of salt is as much salt as you can hold between one finger and thumb: less than 1g. A large pinch is what you can hold between your thumb, forefinger and middle finger all together, which for me is about 3g (it makes little difference whether it is sea salt flakes or fine salt).

Of course, one person’s pinch may hold a little more than another’s (chefs often seem to have huge pinching skills) but since salt is almost always added as a matter of taste, any concerns about this should be taken with a pinch of salt.

Dear Xanthe 

Why do we need to know our onions?

Iqbal, London

Dear Iqbal 

This is a hard one. The phrase seems to have become common in the United States in the early 20th century. There are various theories, including that it refers to Charles Talbut Onions, editor of the Oxford English Dictionary for the first half of the 20th century, or to S G Onions, who created toy coins that were used to teach shillings and pence to children in the 19th century.

Another possibility is that it relates to the French phrase “S’occuper de ses oignons” meaning “mind your own business”, and in translation became “know your own business” or “know what you are talking about”. For cooks, the important point to know about your (sliced or chopped) onions is that it takes at least 10 minutes of gentle frying to soften them properly: no shortcuts, alas.

Recent technical issues relating to the [email protected] email address have now been resolved; if your email bounced back, please try again!

READ MORE:  Dear Xanthe: 'How can I achieve consistently good cakes using American cups?'

READ MORE:  Dear Xanthe: 'What are the white patches that have appeared on my pickled peppers?' ​