Good to know that you are keen to be a food critic. The most important prerequisite for this would be a passion for food, good taste buds, creativity and exuberance. It takes some time to understand the job and be a fair critic. One needs to know the relevant historical facts and interesting data related to the raw ingredients and the food product itself.Being a critic is not only for the dish, but for the hotel's ambience, staff courtesy, pricing, way food is served and the whole experience, if you are too harsh and curt, industry will not like you, if you are too generous and not accurate people won't like you, so it's a balance of both.
Pizza is popular with youngsters and teenagers, you are writing a blog or commenting or doing a live food show, the quality of your presentation will enhance if you knew that it was invented in Italy in 1880's for Queen Margherita, or the nutritional value etc. Similarly knowledge of ethnicity and the evolution of their food habits are also very useful.
Some of the preferred or useful qualifications or knowledge for a food critic is a background or a bachelors degree in journalism, English (or regional language or writing) and communication skills. If you are serious and contemplating a career change then you can think of these correspondence courses which would take you in the higher ranks of the industry
MBA in hotel management (covers food and beverages)
MBA in hospitality management by IGNOU
Diploma in Food & Beverages
If you are new to this, then the easiest way to start is flipping through the supplements of the common newspapers that you get. Most of them carry a food and kitchen section once a week, wherein dishes, recipes, hotels etc are reviewed as a short write up.
You can watch videos and food shows to observe how the show anchor performs. Then focus on one sub-set i.e Chinese, European or offbeat cuisine or traditional but unusual Indian recipes. Then gradually think of starting your own food blog and keep writing, once time and content increases, your traffic will increase. write clearly and concisely with impressive good pictures. In your blog or website add on favourite foods, healthy food, food health tips, festival foods etc to make it interesting.
Meanwhile use your contacts to get you to critic small restaurants and present in regional tv channels, paper supplements etc. You can also explore street food or small but hugely popular mobile food vendors in your area and be using your creativity make it an attractive short presentation. With your network or persistence try to meet some popular chefs and food critics in your region or a 3-5 star hotel to get an inside peek into the food industry. Once you are a couple of months into this, you'll realise your potential and then you can decide to be a part-time food blogger or a full time professional in the food industry.