Della Callagher died and more than 30 other diners became seriously ill after eating Christmas lunch at Ember Inns pub the Railway Hotel in Hornchurch, Essex on Christmas Day 2012.
The pub's manager Anne-Marie McSweeney and chef Mehmet Kaya were found guilty of perverting the course of justice for falsifying food safety records after the outbreak.
M&B was found guilty of placing unsafe food, namely turkey meat, on the market by not ensuring food hygiene rules were followed. The pubco now faces a fine with sentencing adjourned to 8 January.
Prosecutors said the food was not allowed to cool when it was first cooked and then not properly reheated, creating a “perfect breeding ground” for clostridium bacteria.
McSweeney and Kaya disposed of all the waste food, preventing health inspectors from taking samples, and forged kitchen records after the outbreak, Snaresbrook Crown Court heard.
According to reports, checks on other Ember Inns pubs in the area showed that food safety standards were not enforced by the pubco.
In a statement, M&B said: “Mitchells & Butlers respects the court’s decision. We also note that Anne-Marie McSweeney and Mehmet Kaya were found guilty of perverting the course of justice.
“We have taken this matter extremely seriously, and have co-operated fully with the local authority throughout their investigations. Food safety is our highest priority and our employees are required to adhere to these stringent procedures at all times.
“Our thoughts remain with the Callagher family during this difficult time.”