Early gas production in Cheddar cheese is a sporadic and recurrent problem. In this article the major causal agents of unwanted gas production are discussed and potential gas producing organisms in Cheddar cheese are identified. Many of these agents will also cause problems in other cheese varieties. Early gas production in Cheddar cheese results from a number of interacting factors including lactose and citrate levels in the curd, the temperature of curd/cheese during pressing and curing, the salt in moisture level in the cheese and the levels of gas-producing, non-starter lactic acid bacteria in the cheese.