Jacobs, who was honoured by the Queen in 2009 for services to the food industry, goes on to say that restaurants put themselves on the line daily.
"I know many think that such sites [as Zomato] are the way of the future but endorsing them is not what I choose to do."
The email was sent in reply to an invitation to attend a black tie Zomato Restaurant Summit event at Shed 10, in central Auckland, tomorrow.
Zomato spokeswoman Yatchi Yan hit back at the perceived food snobbery, saying the website was a positive service enabling "anyone and everyone to comment on their experiences".
The site states its goal is to "ensure that every meal, for all our users, is a great experience. Share your gastronomic journey with your friends."
Yan said systems were in place to protect restaurants from unwarranted attacks from anyone with a grudge. But an unrepentant Jacobs told the Herald on Sunday online review forums gave a voice to people who may offer their thoughts on food when "in a bad mood that day" or who might be in an "alcoholic haze".
"The average punter is entitled to an opinion, but when it comes to restaurant and food reviews, the ability to eat is not enough," she said.
She questioned how online review sites moderated feedback, including negative reviews that might be written by "an enemy of the restaurant" or a "glowing report" that could be written by a staff member.
"I've heard of people that are posting 20 reviews a week, it's impossible to eat that much, or afford it," she added.
Top chef Ben Bayly of The Grove, told the Herald on Sunday he was all for patrons sharing their thoughts on dining experiences.
"The public has a right to express their opinion, absolutely, I'm 100 per cent behind that," he said.
But he was also aware of the risk of some forums being hijacked by people with agendas.
"Online reviews are often not made with the person's actual name or contact details, in which cases we, as the service provider, have no way of responding - to discuss and resolve something or thank them for their feedback," he said.
"Whenever we get an email through to say a new review has been posted for our restaurants, I investigate it."
Herald on Sunday columnist and restaurant critic Peter Calder said information on the internet, including reviews from amateur foodies, shouldn't always be taken on face value.
"Ninety-nine per cent of what is on the internet is crap and you can't really help anyone who doesn't already know that," Calder said.