Stale bread is usually described as dry. Moisture does move within a loaf as it ages, but research on staling places the central cause in how the starch in the crumb changes over time. Understanding that change is the starting point for keeping bread soft for longer.
It matters commercially too. A review of staling research in Comprehensive Reviews in Food Science and Food Safety opens by describing staling as a cause of significant bread waste around the world.
What happens to starch after baking
Starch does not dissolve in cold water. As water is heated, a review of thickening agents in the Journal of Food Science and Technology explains, it penetrates the starch granules and they swell. In a baking loaf, that swelling is part of how the crumb sets.
Once the bread cools, the starch molecules gradually re-associate into more ordered structures, a process called retrogradation. The staling review confirms the central role of amylopectin retrogradation, together with the redistribution of water between the polymers in the crumb. It also points to proteins and non-starch polysaccharides as contributors.
The flour matters as well. In a 2024 study on steamed bread, the authors linked wheat varieties with longer amylopectin chains to faster retrogradation.
Why the fridge is no friend to softness
The same steamed bread study stored bread at room temperature (25 °C), chilled (4 °C) and frozen (−18 °C). Storage at 4 °C, and cycling between 4 °C and room temperature, produced more ordered starch structures than the other conditions, and the authors note that this kind of temperature cycling is used deliberately to increase retrogradation.
Steamed bread is a different product from a baked loaf, so treat this as an indication rather than a rule. For a product sold on softness, it is a good reason to test shelf life at the temperature the bread will really be kept at.
Ingredients that slow staling
The staling review groups the ingredients most studied for retarding staling into three types: hydrocolloids, waxy wheat flours and enzymes.
How maltogenic amylase works
Maltogenic amylase is one of the enzymes used for this. A 2023 review in Carbohydrate Polymers describes it as widely used to extend the shelf life of bread: it softens bread, improves its elasticity and preserves its flavour without affecting dough processing. It mainly produces maltose.
A 2026 study in the Journal of Agricultural and Food Chemistry summarises the mechanism: the enzyme hydrolyses starch and, in doing so, retards staling by inhibiting starch retrogradation.
Both papers point to the same limitation. The enzyme's thermal stability does not always meet the demands of high-temperature baking, which is why work continues on more heat-stable versions. In the 2026 study's baking trials, the more heat-stable variants were better than the original enzyme at maintaining bread elasticity and delaying hardening.
Enzymes slow firming. They do not stop mould. Staling and microbial spoilage are separate problems. A loaf can stay soft and still spoil, so a shelf-life target needs both addressed.
Running an anti-staling trial
- Define shelf life as the customer experiences it: the storage conditions, and the day the last slice is eaten.
- Measure crumb firmness on fixed days, against a control baked the same day.
- Compare enzyme preparations on performance in your bread. Activity is often expressed in units specific to each supplier, so labels and unit counts do not compare directly.
- Hold the bake profile constant during the trial, since heat affects how long an enzyme stays active.
- Assess eating quality alongside instrument firmness. Softness that turns gummy is not the goal.