Most organic food doesn't actually taste better than food produced with the use of pesticides, cookery writer Darina Allen told the meeting.
"I wouldn't say organic food always tastes better. Freshness is hugely important, and very often doesn't taste better when it has been sitting on the shelves of a supermarket for long periods."
About 85 per cent of organic food is sold in supermarkets, at markups of up to 200 per cent, the meeting heard, with the remainder sold independently through farmers' markets or direct to the customer.
Ms Allen said the price of organic food depended on where it was bought, and usually the most expensive place to buy it was the supermarket.
She expressed alarm at the "steep decline" in the level of nutrients found in intensively produced foods.