Scientists have found that almost half of the orange juice served in cafés and restaurants could be contaminated with dangerous bacteria such as salmonella.
Researchers at the University of Valencia analysed 190 batches of juice from a number of cafés, restaurants and bars in Spain.
Under EU regulations, 43% contained 'unacceptable' levels of enterobacteriaceae, the bacteria family, which includes salmonella and E. Coli.
One in 10 samples contained unacceptable levels of mesophilic bacteria, which thrive in room temperature.
Salmonella was found in 0.5% of the samples, and Staphylococcus aureas – which can cause skin infections – was found in 1% of them.
More than 80% of juice kept in metal jugs contained unacceptable levels of enterobacteriaceae, compared to just a fifth of juice samples served freshly squeezed into a glass.
Researchers believe dirty juicers and serving jugs are responsible for the levels of bacteria. They warned caterers to ensure machines are thoroughly cleaned and to serve the drink immediately after squeezing.
The problem is thought to stem from a large amount of juice being squeezed in one go and then left in stainless steel jugs where it heats up, allowing bacteria to thrive.
Study author Isabel Sospedra, whose findings were published in the journal, Food Control, said: "Some orange juice is consumed immediately after squeezing but many cases it is kept unprotected in stainless steel jugs.
"We found that some juices that were kept in metal jugs presented unacceptable levels of enterobacteriaceae in 81 per cent of cases and in 13 per cent of cases with regards to mesophilic aerobic bacteria.
"However, when the freshly squeezed juice is served in a glass, these percentages fall to 22 per cent and two per cent respectively."
She added: "Juicers and juicing machines have a large surface area and lots of holes and cavities. This promotes microbial contamination, which is picked up by the juice as it is being prepared.
"To ensure consumer health, we recommend that juicers are cleaned and disinfected properly. The same goes for the jugs in which the juice is stored, although its consumption is better as and when it is squeezed."