A major precursor of monochloropropanediols (MCPDs) in leavened cereal products is glycerol, which is formed as a natural by-product of yeast fermentation. However, yeast metabolism is affected by stresses such as low osmotic pressure from e.g. the incorporation of sugar or salt in the dough recipe. Tests with cooked model doughs have shown that glycerol production was proportional to yeast level and limited by available sugars, but high levels of yeast inhibited MCPD formation. Added glucose did not increase the production of glycerol but did promote the generation of MCPDs. This effect was attributed to the thermal generation of organic acids from added glucose, so the effect of pH and short-chain organic acids on MCPD generation was measured. There was a good correlation between initial dough pH and the level of MCPDs generated. The effect was weaker than that predicted by simple kinetic modelling, suggesting that the involvement of H+ and/or the organic acid was catalytic or not rate-determining.