Diners should be cautious of food premises which don't display their hygiene rating, say environmental health officers.
Officials in Lincoln carried out 634 inspections in 2012, leading to 12 hygiene improvement notices and 292 written warnings.
Three operations – Bowser Brothers hog roast at Lincoln Christmas Market, the Great Wall Chinese takeaway, St Giles, and Ye Olde Crowne, in Lincoln – were prosecuted over their failings.
The City of Lincoln Council adopts the Food Standards Agency's ratings scheme which measures businesses' compliance which food safety law.
There are six ratings ranging from 0/5, meaning urgent improvement is needed, to the generally satisfactory 3/5 through to the very good 5/5.
Nearly 600 of the city's 1,100 eateries have achieved the top ranking.
Yet businesses do not have to display their credentials.
Even those with a zero rating can stay open if an imminent public health risk – for example, rats or cockroaches in a kitchen – cannot be demonstrated.
Officers can ban the use of specific equipment in some cases, say at a butchers where cooked and uncooked meat have been put through the same slicer.
Louise Harding, environmental health officer, said: "We issue every business we visit with a sticker and certificate showing their rating but we cannot make them display it.
"I don't think you would see anyone in the city with ratings of zero, one or two displayed so the message is: if you don't see anything displayed you need to ask questions.
"You can check the rating of a food business online at food.gov.uk/ratings
"What we are finding is that in the current economic climate some businesses are cutting corners, for example, not buying the right sort of cleaning materials.
"Some places have had the electricity cut off and still been operating.
"We have seized food and removed stuff from sale where businesses have not been able to prove where it has come from.
"I recently took eggs from a business which had tiny cracks in them and were not Grade A, which posed a salmonella risk.
"Food hygiene training is an issue – people who know they should keep things clean and store raw meat at the bottom of a fridge and cooked stuff at the top but the understanding why is not there."
The FSA four Cs strategy – cooking, cleaning, cooling and avoiding cross-contamination – aims to prevent food poisoning from domestic and commercial kitchens.
There are about 120 cases of E. coli, salmonella and Campylobacter each year in Lincoln.
Sara Boothright, the council's food and health and safety manager, said: "In terms of 'Joe Public', what we know is there is still quite a high proportion of food poisoning in the home.
"We visit homes in these cases and try to identify if there's any specific source but it's not an exact science.
"It could be something from up to seven days before that makes you ill.
"There are people running businesses who don't appreciate what they should be doing.
"There are those who blatantly disregard rules and others who are lazy.
"About three per cent of the registered food premises in Lincoln are non-compliant, down from five per cent pre-2011.
"We now work with those non-compliant businesses for longer to raise standards – we have made members of the public our customers, not the businesses."
Des Anastasiou, owner of Burton Road Chippy, in Lincoln, proudly displays his 5/5 rating at the premises.
"It is not difficult to obtain 5/5 providing that the premises are clean, you keep a cleaning rota and log the temperatures of food," he said.
"Every morning we check that equipment is running correctly – for example, if fridges are at the right temperature, and if anything is wrong we solve the problem.
"We also do closing checks at the end of day. We keep a record of all the names of our suppliers. If someone bought fish here that was not very good we can trace the source.
"It's good for business if your establishment is clean and people have the confidence to come in and eat.
"We display our 5/5 rating and it should be made the law for all premises to display theirs. It's unfair to businesses that do try to get it right."