Freezing 'could help food bugs'

Cook thoroughly: That's official advice

Meat that has been frozen then thawed is a far easier target for food poisoning bacteria, claims a scientist.

He says that consumers should be far more careful about eating frozen meat as soon as possible after defrosting it.

Some food freezing methods appear to be far safer than others, he adds.

Ashley Wilson, the director of the Centre for Cell and Tissue Research at the University of York, used an electron microscope to compare the internal texture of thawed meat with that of fresh meat.

Essentially you leave the ideal medium for the spread and reproduction of bacteria

Ashley Wilson, York University

He found that during the freezing process, the formation of ice crystals opens up an interconnecting network of tiny gaps.

When the food is thawed, these become microscopic canals throughout the flesh, filled with protein-rich liquid.

These, according to his theory, make it easier for bacteria to penetrate deep inside the meat.

In fresh meat, bacteria are principally confined to the surface.

Unscrupulous butchers

He told BBC News Online: "On fresh meat, you have infection in two dimensions, but after it is thawed, it's 3-D.

"Essentially you leave the ideal medium for the spread and reproduction of bacteria."

He said that it was likely that frozen-thawed food would go off much sooner - and that even if cooked thoroughly, there could still be a problem.

He said: "The problem is the toxins produced by the bacteria rather than the bacteria themselves, and these are harder to destroy."

Current UK legislation obliges food manufacturers to state clearly on packaging if the food has been previously frozen, even if sold in its thawed state.

However, Ashley Wilson told BBC News Online that he was aware of butchers who were "unscrupulous" when it came to correct labelling on this issue.

He said that he now intended to team up with a microbiologist to try to assess the extent of the extra risk - and to check whether freezing and thawing vegetables could have a similar effect.

A spokesman for the Food Standards Agency said that its advice would be to cook meat thoroughly, regardless of whether it had been defrosted or not.