If you look at the research tree, there are researches that gives + food and certain building unlocks will produce food. Try researching those trees first. Be careful of buildings that consume food. As if you have many towns, and build certain buildings like Markets, it will make your surplus food into negatives. Pro Tip: Read the little notes that tells you if it will consume or produce food.
[Edited by Ravenitrius, 3/16/2011 2:33:01 AM]
Its probably the markets then.. since my research for farming tech is done