Drivers can still drink wine-laced dishes '˜as long as chef keeps the lid on'

Scientists have discovered that leaving the lid on while cooking is one of three key factors to control the amount of alcohol in the finished dish.

Health worries or fear of being over the limit often put mums-to-be, slimmers and drivers off menu items that include a red or white wine sauce or a meal laced with beer.

Doctor Pia Snitkjaer, of the Department of Food Science at the University of Copenhagen in Denmark, carried out a series of experiments to work out how to control the alcohol content during cooking for the benefit of large kitchens, the food industry, the gastronomy and restaurant sector as well as in the kitchen at home.

Dr Snitkjaer said: "In the experiments I used 900 mls of veal stock plus 150 ml beer or wine.

"At this mixing ratio, the alcohol concentration starts at around two per cent but drops to 0.2 per cent after half an hour of cooking."

She said precisely how much alcohol is left in, for example, a red wine sauce depends on three factors that need to be checked to control the alcohol content in a liquid dish or sauce.

They are: how much the dish is reduced, whether it is cooked with or without a lid, and how much alcohol is added from the start.

Dr Snitkjaer said: "One should remember that you typically eat only 1/2-1 decilitre of sauce.

"If we, for example, assume that you eat 100 ml sauce, with a concentration of two per cent volume it corresponds to an intake of 2ml of alcohol. There are 15 ml in a unit of alcohol, so a pregnant woman would also be able to handle it,"

All other factors the researchers studied - including the dimensions of the saucepan and the cooking temperature - proved to only be significant because they could affect how quickly the sauce was reduced.

Associate Professor Jens Risbo, also of Copenhagen University, has developed a model that shows how the alcohol behaves in liquid dishes.

That it is the volume of the dish that is the best parameter for determining the alcohol content - and not the cooking time - matters in relation to which techniques people can use if they want to reduce the alcohol content in the finished dish.

Dr Snitkjaer said: "You can reduce the alcohol content quickly by bringing a dish to a rolling boil, because by boiling hard, the volume will also decrease rapidly.

"But if you do not want the food to boil down too much, you can keep adding water as water evaporates, which will also lower the alcohol content both by dilution and evaporation.

"By placing a lid on the saucepan, there is a kind of reverse distillation where the alcohol disappears even more rapidly from the saucepan than the water. This is because alcohol is more volatile than water and thus can more readily evaporate.

"This is the same effect you use when you distill alcohol - you heat it up, so the alcohol evaporates more than the water, after which you can condense the vapours and obtain more concentrated alcohol."

She said the lid doesn't sit tightly on the saucepan, allowing the steam to escape under the lid so that the alcohol evaporates, while the water condenses more preferential on the colder lid and runs back into the pan.

As it cooks, more and more alcohol escapes under the lid, while the contents of the saucepan will contain a higher percentage of water.

Experiments show that the use of a lid has a dramatic effect on obtaining a low concentration of alcohol.

Dr Snitkjaer said booze contains a lot of calories, but will probably be listed in a recipe with the calorie content the alcohol has as an ingredient before it is actually added to the dish, which results in a "misleadingly high result."

She added: "How many fewer calories there are depends on how much alcohol is evaporated.

"One gram of alcohol gives about seven calories, so every time you evaporate one gram of alcohol, you have seven fewer calories in the saucepan.

"It would be nice to be able to say precisely what this means for a tomato soup, a meat dish, et cetera.

"There are many things that can vary the result, but you can get some ideas about what happens when some of the most important parameters are changed - for example, what happens if you have a lot of sugar or a lot of gelatine, such as in a veal stock."