Glan Clwyd Hospital in Bodelwyddan had a two-star "improvement is necessary" rating in May in a report warning of major non-compliance with regulations.
Denbigh Infirmary's rating of one star was called "abysmal" by Clwyd West AM Darren Millar.
Both have now achieved four-star grades.
Control measures to combat clostridium difficile (C.diff) have also been stepped up at Glan Clwyd and Wrexham Maelor Hospital.
Three deaths between April and June in north Wales were said to be directly attributable to the infection, while it played a part in two others.
The number of cases of C.diff per 100,000 people was 51 in the Betsi Cadwaladr health board area, compared to 36 in Wales and 25 in England.
Tracey Cooper, the board's assistant director of nursing with responsibility for infection prevention, said in a report that the food-hygiene issue had been addressed immediately and a programme of unannounced kitchen inspections had started.
The board will discuss the report and C.diff and MRSA infection rates during a meeting on Tuesday.

The 46-year-old succeeds Ronnie Moore, who parted company with the club by mutual consent earlier on Wednesday.
This is a first managerial role for Hignett, who had a spell as Hartlepool assistant manager under Colin Cooper in 2013-14.
Hartlepool are one place above the relegation zone having lost three of their past four league matches.
Hignett, whose 19-year playing career began at Crewe and ended at Hartlepool, will take charge of the team for the first time when Pools host Yeovil on Saturday.
"We immediately identified Craig as our number one target and we believe he has all the right qualities to help instil confidence back in to the players and help us move up the table," said chairman Gary Coxall.
"He has a wealth of experience in football and has been looking for an opportunity to move in to management so we're delighted to give him that chance here at Victoria Park."
Sam Collins, who worked alongside Moore, will remain at the club but in a new role focusing on the club's under-21 players.
Two Denbighshire hospitals which had serious food safety standard failings uncovered by an inspection have now been given improved ratings.
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Former Middlesbrough player Craig Hignett has been named as the new manager of League Two side Hartlepool.