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Hamburgers Need to be Cooked Properly

13 December 2013

© Nofima (formerly Fiskeriforskning)

To be safe to eat, products made from ground beef must be cooked until they are at least 71°C in the centre.

However, beef that has been in contact with oxygen before cooking becomes brown at a lower temperature and this his is risky from the food safety point of view, according to the Norwegian food agency Nofima.

Consumers should be aware of the risk of eating undercooked products made of ground beef, whether at home or in a restaurant.

Meat comes into contact with oxygen when you ground it in your own kitchen, but also when you buy ground beef packaged in oxygen-rich atmosphere, containing approximately 75 per cent oxygen and 25 per cent carbon dioxide.

This method is used in several European countries.

The advantage of an oxygen-rich atmosphere is that the first few days after packaging, the meat has a more red colour than with most other packaging methods.

A disadvantage is that the colour in the centre of a hamburger cannot be used to measure whether it is thoroughly cooked or not.

Many People Judge Whether Meat is Cooked by Colour

cooking hamburgers properly
When ground beef has been packaged in an oxygen-rich atmosphere, it becomes brownish grey and looks cooked through when it reaches 60°C, while beef packaged with oxygen-free gas mixtures or in vacuum needs temperatures above 71°C to achieve the same colour.

In a research project led by the food research institute Nofima, Norwegian consumers were asked whether they make hamburgers at home from ground beef or whole muscle meat and how they judge whether a hamburger is thoroughly cooked.

The answers showed that making hamburgers at home is common and that many people use colour as a guide to whether the meat is properly cooked.

Laboratory tests were also carried out, to look at the connection between killing dangerous E. colibacteria and colour change during cooking.

"Hamburgers should be cooked until they are at least 71°C in the centre so as to kill bacteria; then they are cooked through and safe to eat," said Solveig Langsrud, Research Scientist at Nofima.

The results showed that, for vacuum packaged ground beef, a change in colour from red or pink to brown is a good indication of whether the hamburger has been cooked enough to kill bacteria. This was not the case for oxygen packaged meat.

"Beef that has been packaged in an oxygen-rich atmosphere already looks cooked through when it reaches 60°C," said Oddvin Sørheim, scientist at Nofima.

E. coli Can Cause Serious Illness

Most bacteria on meat are completely harmless, and with good hygiene and routines at butchers and in shops the level of bacteria on meat will be low.

But regardless of the routines, meat is a biological material that can occasionally contain dangerous bacteria.

One example of a bacterium that can cause serious illness, even in low numbers, is Shiga toxin-producing E. coli.

Children are particularly vulnerable to these bacteria.

To be completely safe, it is important, in addition to maintaining good kitchen hygiene, to cook hamburgers and other minced meat products long enough to kill these bacteria.

It is important that the consumers themselves take responsibility, especially when preparing home-made hamburgers to children.

Because consumers make and cook their hamburgers in different ways, it is difficult to give concrete advice about how to ensure that hamburgers made from ground beef packaged in an oxygen-rich atmosphere are thoroughly cooked.

The laboratory tests showed that it is difficult to measure temperatures during frying or grilling, and neither is there any suitable thermometer probes for this on sale.

This work has been carried out by Nofima as part of a four-year research project that is intended to increase food safety for consumers.

The research project is financed by the Foundation for Research Levy on Agricultural Products and the Research Council of Norway.

November 2013

© Nofima(formerly Fiskeriforskning)

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