Some of us defrost meat in the microwave to save time when we’re busy, or because we forgot to get the joint out of the freezer in time for it to defrost before cooking, but is this practice actually safe? Not according to Professor Costas Stathopoulos of Abertay University in Dundee.

Our microwaves have a defrost setting on them, but Prof Stathopoulos says it’s not wise to use it to defrost meat. The standard advice for defrosting meat has always been to do it in the fridge, because the cold temperature slows down bacterial growth.

Prof Stathopoulos says that microwaves are not great for defrosting frozen meat because some areas of the food become warm and start to cook before the other parts are thawed. That means you end up with overcooked parts in the meat. The USDA says that defrosting in the microwave is safe, but because it can bring meat temperatures into the danger zone where bacteria multiply quickly, it must be cooked as soon as it’s defrosted.

You should never defrost meat in hot water either

You should never defrost meat in hot water either, say both the USDA and Prof Stathopoulos.

Only one in 10 people actually feel confident that they know how to safely freeze and defrost food, the Prof reveals on Inside the Factory, a food program on BBC 2.

On the show, Prof Stathopoulos shows his co-presenter Cherry Healey how much bacteria grows when meat is thawed after being frozen. He compares two samples of turkey meat in petri dishes – one thawed in the fridge, and the other defrosted at room temperature by being left out on the counter. The turkey left at room temperature is shown to have twice the amount of bacteria than the meat left to thaw in the fridge. These bacteria included dangerous E.coli organisms.

Prof Stathopoulos also says that re-freezing food that was previously frozen will cause bacteria to multiply and make the food unsafe to eat, as you are re-freezing more bacteria. However, the Prof reveals that you can re-freeze cooked food, even if it was previously frozen when raw.

How long can you keep food in the refrigerator?

Prof Stathopoulos says you can keep food in the freezer for up to six months, but after that it will start to lose its quality.

Professor Keith Warriner at the University of Guelph in Ontario disagrees with part of the Scottish university study. He says that the best way to defrost foods is in a sink full of cold water, as the heat transfer is faster and more even.

Whichever way you defrost your meat, it’s important that it reaches a safe internal temperature while cooking, in order to kill the bacteria. Invest in a good meat thermometer and keep your cooking area clean.