IF EGGS could be pasteurised as easily as milk, thousands of people could be spared salmonella poisoning every year. But until now, efforts to make eggs bug-free have met with a mixed reception. What鈥檚 OK in the US, for instance, is banned in Europe.
There鈥檚 a clear need for a way of pasteuri-sing eggs. According to Britain鈥檚 Public Health Laboratory Service, there were nearly 11,000 cases of Salmonella enteritidis poisoning last year, and eggs are a frequent culprit.
Salmonella mainly gets into eggs inside the hen鈥檚 ovary or oviduct, before the shell forms around the yolk and white. It can also get in after the egg鈥檚 laid, from external sources like muck on the farm.
Advertisement
While pasteurising milk is a simple matter of heating it to kill any bacteria, doing the same thing to an egg by bathing it in hot water isn鈥檛 allowed in Europe. That鈥檚 because the water removes the thin coating around the shell, called the cuticle. European Union regulators fear that with the cuticle removed, bacteria will enter the treated egg through pores in the shell.
Now Leda Technologies of Antwerp in Belgium reckons it has the answer. Instead of using a water bath to heat up the egg, it鈥檚 developed a system that uses steam and ultrasound to do the job. Leda says that it can pasteurise an egg without destroying the cuticle, leaving it raw, soft-boiled or hard-boiled. It hopes the system will soon be in restaurant kitchens across the continent.
First, a small ultrasound device produces low-temperature water vapour in a trough below a tray of eggs. This coats them in an ultrathin layer of water. The chamber is then flooded with steam to warm the eggs to around 60 掳C. Leda has found that having the eggs already moist makes them warm up faster鈥攕o there鈥檚 less risk of the egg cooking.
Crucially, water is not being washed past the eggs, so the cuticle layer stays put. Leda says it takes 40 minutes to pasteurise an egg so it remains beatable (rather than 2 hours without moistening it). Additional blasts of ultrasound are then directed at each egg to ensure each gets hot enough at its core to destroy bugs鈥攁gain, without cooking it.
In the US, they don鈥檛 think that removing the cuticle adds to the risk of food poisoning, as the salmonella鈥檚 already inside the egg. Four years ago, the Department of Agriculture approved a simpler pasteurisation technique (快猫短视频, 16 May 1998, p 17). This warms eggs in a series of water baths to a temperature that kills the bacteria.