Serious concerns have been raised about food standards in more than half the wards at Kent and Canterbury Hospital.
Environmental health bosses say patients are being served up meals from kitchens that are not up to scratch since Serco took over the food contract there last year.
Officers from Canterbury City Council gave the hospital a food hygiene rating of two out of five after an inspection and demanded improvements are made.
Breaches include nurses storing their own food in patient fridges and non-catering staff entering kitchens – some without using handwash first.
The officers found standards were worst in kitchens serving Treble, Marlowe, Taylor, Harbledown, Mount and McMaster and Harvey wards and said major improvements were needed.
"They managed to get some ward kitchens up to speed, but there were problems in others with things like ventilation..." - inspector Sarah Maloney
Meanwhile, Taylor and Invicta wards were branded satisfactory and Brabourne, Clarke and Kent wards, the Clinical Decision Unit and the Emergency Care Centre were deemed good.
But the Food Standards Agency said departments could not be given separate ratings and ruled the lowest score had to apply to all wards.
In her report, the city council's team leader for environmental health, Sarah Maloney, said some facilities were excellent - but raised fears about a lack of equipment and ventilation in others.
She uncovered significant hygiene issues, including finding out-of-date personal patient food in fridges and said despite training there was still confusion and inconsistency.
Ms Maloney also said safety systems were not always being followed and - while cleaning was generally good - there were terrible ventilation issues in some of the kitchens.
Problems crept in after Serco was hired to introduce a more flexible way of serving meals, by moving food preparation from one big kitchen to 13 ward kitchens.
Ms Maloney said: "It is more of a 'meals on wheels'-type service where meals are stored and reheated in individual wards. However, their kitchens vary hugely in terms of size and facilities.
"They managed to get some ward kitchens up to speed, but there were problems in others with things like ventilation.
"Some of them are brilliant, lovely and clean, with separate facilities for staff, but others are not.
"It’s been a roll out of something quite complicated. It's taken a while to bed in, and perhaps should have been done slower. But where it's working, the new service is good."
She added: "There are no immediate risks to health. None of the problems will give imminent risk to patients, but improvement is necessary."
Ms Maloney plans to inspect the hospital again in September, when a different score may be given.
Hospital bosses say changes have already been made since March - and that they expect to receive a higher rating after the next inspection.
Matron for nutrition and quality improvement Wendy Ling Relph said: "We introduced our ward kitchens to provide excellent, consistent food for our patients from a significantly wider menu.
"At the time of the environmental heath officer visit they found that ward staff were using the ward kitchens for water, washing up and refrigeration and that is why they were marked down.
"Since the visit in March we have reminded staff not to enter ward kitchens, provided staff welfare facilities on two wards and agreed locations for a further five wards.
"We have also already provided additional fridges in wards for storage of staff or personal patient food. Following these changes we anticipate a return to a higher rating when re-assessed in the autumn and a '5 star' rating in 2015.
"Our food continues to get excellent feedback from our patients, with our May survey on catering showing overall satisfaction of 97.78%."
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