A Japanese chef told me that I should always chill tempura batter to ensure it remains light, crisp and fluffy after it is cooked. How does chilling achieve this?

Tom Dressler, Amarillo, Texas, US

If, after peeling an onion then topping and tailing it, I wait before chopping it, the middle segments push up and outwards (see photo, right). Why?

Alan Middleton, Weymouth, Dorset, UK

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About 30 years ago, I gave up drinking wine as I always ended with a blinding headache after an evening when wine was served.  It seemed to cure the problem and I was told that it was likely to have been the sulphides (preservatives) that had caused the effect.  It obviously saved me a lot of money.  Recently, however, my wife asked me why, when she uses wine in the cooking, I do not suffer the same effect ?  I confessed that I do not know.  Can you explain ?

I've recently been trying to lose weight and am rather pleased with the results. However, there is one instance every day when the craving for food becomes almost agonising.

I have to pass a small food stall in the morning which serves bacon sandwiches. The smell drives me crazy and I'm desperate to buy one, so much so that I've changed my route to work to avoid it.

A vegetarian friend also tells me that the one smell that could almost make her start eating meat again is that of bacon grilling.

So what has cooking bacon got in it that makes it so tempting?

Peter Hodge, Leicester, UK

My girlfriend and I were having an argument the other day. Sometimes when it is cold in the kitchen, I turn in the gas hob to warm the place up. The argument is that she claims that the room gets hotter if you put a pot of water on the hob to boil and let the room get steamy. I disagree and think that the room gets just as hot without boiling a pot of water.

Who is right? Does the room get hotter with the pot of water or does the room get just as hot without it?

Help me settle a long-running question in my house. My wife says that for cooking, water should always be boiled starting with cold water. Apparently professional cooks do this and the Martha Stewart, Julia Child, etc. types also say it. This is for things like boiling eggs, cooking pasta, etc. where the water is heated completely alone, not as part of the actual cooking process with other ingredients involved.

I say that if you already have warm water at the tap (for example if you were just washing dishes) you can just use that and it might even save a little energy. (If the warm water in the pipe is just going to sit there cooling off anyway, might as well use it. Plus hot tap water must be more efficient than heating a pot over an open flame, right? We have natural gas for both hot water and the stovetop.)

The end result will be boiling water, why would it matter if it started off cold or warm? It's all H20 just with varying amounts of energy.

I start with hot tap water (already a little over 1/2 way to boiling) and it boils much faster (obviously) than waiting for cold tap water to heat, especially since our water is well water, much colder than standard tap water.

I have been told that the substances in gravy react together and bind when they cool - it is not, apparenty just a case of a liquid turning to a solid. I would like to know why this happens, and even hopefully what molecules are involved. Thankyou xxx

Scaling up culinary recipes does not always follow a linear relationship, especially when using spices, salt or alcohol.

For example, for 1 litre of water you might be accustomed to adding 1 measure of salt, but for 4 litres you wouldn't add 4 measures of salt, but much less.

Does anyone know what the explanation for this is?

Cathy Fisch, Orsay, France