We all probably take bread for granted. In buying a loaf we’re not thinking much about its shelf-life, so it’s interesting to consider the keeping qualities of bread. These break down into flavour and texture changes, and spoilage.
Freshly-baked flavours are lost within the first few hours of storage. The texture changes more slowly due to firming and drying out caused by moisture movement from crumb to crust, loss through the packaging, and the process of staling (changes in the starch). All of these affect how attractive the product is to eat, whereas spoilage, due to the growth of visible mould, is a clear "don’t eat me" sign.
Generally, loss of quality is the main problem. A traditional French baguette (remember those?) had a thick, heavy crust with an open, low-moisture crumb. In two to three hours, the water moves outwards to the crust, making it chewy, while the crumb becomes dry.
UK plant bread has an ultra-thin crust and an even, finely bubbled crumb, containing quite high levels of moisture. This design means there is little movement of water, or staling, and the product stays fresh for up to a week.
The most extreme types of bread I have seen are in the USA, where high levels of sugar and fat give a 21-day life, and the Middle East, where flat breads must be eaten within an hour of baking, otherwise they dry out and crack.
So we can design our products to deliver the shelf-life needed by consumers. And preservatives? That’s for another day.