Brain food: A lesson in limes

I made lime marmalade with yellow limes successfully but when I tried it with green limes the result was less than successful, with very tough skin. R. Henley

It has been a sensational year for Tahitian limes this year and from the rest of your letter it seems you have received, literally, a windfall from a neighbour. The dark green ones are simply unripe Tahitian limes. The yellow ones are ripe. When ripe, citrus skin is about 30 per cent pectin; this is a type of starch that forms a gel when cooked with sugar and acid. The rest is much tougher cellulose and hemicellulose. When limes are unripe there are proportionally a lot more of these compounds that don't break down when cooked. As an aside, it's interesting to note that when fruit, such as berries, refuses to set we add a squeeze of lemon juice. This lowers the pH and helps the pectin bond to create a gel. The addition of actual lemon peel, with all its white pith, increases the overall level of pectin.

I read Pigsticks and Harold and the Incredible Journey to my son at bedtime. The hamster is very keen on Battenburg cake. Can you tell me what it is? N. Russo

To help answer this vexing question I am going to refer to the seminal 1980s comedy Blackadder Goes Forth, set in World War I. In one episode the simpering and sycophantic Captain Darling exclaims, "I'm as British as Queen Victoria!", to which the sardonic Captain Blackadder, played by Rowan Atkinson, replies: "So your father's German, you're half German, and you married a German!" The Battenberg cake is made from plain and coloured sponge cake cut into four long, square fingers, arranged in a chequered pattern, held together with jam, and encased in almond paste. They are distinctly English and first appeared in the late 1800s after the marriage of Queen Victoria's granddaughter Princess Victoria of Hesse-Darmstadt to Prince Louis of Battenberg​. Prince Louis later took British nationality and anglicised his name to Mountbatten. The Battenberg cake is surprisingly easy to make and is delicious, especially if one makes one's own almond paste. An excellent recipe, tested by yours truly, can be found in Phillippa's Home Baking by Phillippa Grogan and Richard Cornish (Penguin Lantern).

Can I use cooking spray on non-stick frying pans? R. Vidler

Yes. But the lecithin in the spray may cook on and can cause build-up and hinder the non-stick properties of the surface. Also consider some manufacturers' warranties may become void if spray is used. Some retailers suggest spraying the food itself before adding it to the pan. The very idea, however, appals me. A smear of olive oil on a not-too-hot steel pan works just as well.

I want to recreate the famous salt-cod-stuffed piquillo peppers we devoured in Spain. Can you buy them here in Australia? Other than the jarred variety? J. Argall

Sorry to bore readers with stories of Spain but you will ask questions about Spanish cuisine. I was in a bar in Seville and had the most sensational piquillo peppers – they are like long red capsicums. Juicy and smoky, they were sensational. I asked the chef how he cooked them. He said: "I get my wife to open the tin." Spanish conserved foods are generally of exceptional quality. It comes from the tradition of poverty, when canning was comparatively expensive and therefore only the very best was put into cans. So I can recommend Spanish piquillo peppers. If you want to start from scratch, red bullhorn peppers are an acceptable substitute. Look for them in farmers' markets and greengrocers in suburbs with a large Mediterranean population.

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