Helen Barber, of Te Aro, asks :-

I have a number of old brass containers, a jug and some platters/trays that were fashionable about 60 years ago. I am scared they may contain lead or other metals that may contaminate the food. Are they safe to use with food?

Ian Shaw, a toxicologist at the University of Canterbury and author of "Is it Safe to Eat" and "Food Safety - the Science of Keeping Food Safe", responded.

Brass is an alloy of copper and zinc which might also contain very much lower concentrations of other metals including aluminium, iron, manganese, nickel, tin and lead. Since the latter metals are at much lower concentrations they are not as important in the context of toxicity, but they should not be forgotten because several of them – particularly lead and aluminium – are toxic following prolonged exposure.

Both copper and zinc are toxic (except at very low doses which are indeed beneficial). They are both pretty well insoluble in water, even boiling water, but are very much more soluble in acids and bases. This means, for example, that if you make chutney (with vinegar) in a brass pan you are likely to dissolve sufficient copper and zinc from the brass to make the resulting chutney toxic. Similarly, if you serve acid or basic food on a brass platter the zinc and copper will dissolve in the food and make the food toxic.

Therefore, to be sure that food cooked in or served from brass containers is safe you would need to know the pH of the food. I think it is unlikely that most of us would want to test the pH of food before we cooked it or served it from our nice antique brass vessels and so, on balance, it would be better not to use such vessels in contact with food.

You could try a very simple experiment to demonstrate this. Put a few drops of vinegar on one of your brass vessels and leave it to stand for an hour. When you return you will see that the vinegar has turned a blue-green colour because of the dissolved copper.

Interestingly, some cooking processes benefit from very low copper concentrations. For example, egg whites beaten in copper or brass bowls make very much better meringues that when glass, ceramic or stainless steel bowls are used. This is because copper ions bind to the protein molecules in the egg white joining them together to make a more stable, air trapping structure. So copper is not always bad in the kitchen!

Other alloys encountered in cookware and serving/drinking vessels also deserve our attention. For example, pewter – an alloy of tin, lead, antimony and copper – was used extensively to make plates and tankards in days gone by. Its components are all horribly toxic on their own, but when combined in the pewter alloy they are far less chemically available and so less problematic. Despite this, I would not eat off pewter plates, but I do drink my Sunday night pint of beer from an old pewter tankard.

Lead on its own in a culinary context is a very different matter. The Romans used lead cookware and frequently used verjuice – an acid ferment of unripe grapes – to cook with. This would mean that their food contained high levels of lead. This, in conjunction with lead in their water supply from lead pipes, led to sufficiently high lead intakes to cause brain damage which is thought to have been a contributing factor in the downfall of the Roman Empire.