The shelf life of bakery products is often shortened by micro-organisms (mainly yeasts and moulds) that grow on the surface of the product.
This happens faster in products that have a high moisture content, such as bread, than in lower-moisture products, such as cakes, but shelf life can vary within each category.
The term ‘water activity’ (aw) is used to describe the level of available water in a product and is measured on a scale of 0 to 1. Products with a lower aw value have a longer shelf life.
Baked products like cakes and bread usually have an aw value between 0.70 and 0.98. Some products may contain fairly high levels of water, but still have a low water activity because the water is bound osmotically by the soluble constituents of the food so it’s not available for micro-organisms to use. You can reduce the water activity of a product by adding more sugar and salt, so recipes which contain more sugar generally have a longer mould-free shelf life.
Andrew Hughes, senior bakery specialist, Campden BRI
Campden BRI provides technical support to the food, drinks and allied industries worldwide. Its activities are built on a programme of industrial relevant research and innovation steered by industry. See campdenbri.co.uk or telephone 01386 842000