The falling number test times, in seconds, how long a plunger takes to fall through a hot paste of flour or ground grain and water. It measures alpha-amylase activity: rain-damaged, sprouted grain gives a low number and sticky bread, while a very high number can mean weak fermentation.
How the test works
A weighed sample is mixed with water in a tube, heated in a boiling bath and stirred. The starch gelatinises and thickens the paste, while alpha-amylase breaks it down again. The plunger is then released, and the time it takes to fall is the result, including the mixing time. ISO 3093 (Hagberg-Perten) is the reference method, with a correction for altitude.
Why buyers care
Low values mean a lot of enzyme, usually from rain at harvest that started germination inside the kernel. Bread from such flour has a sticky, gummy crumb and slices badly. Low-falling-number wheat is often sold as feed.
High values mean little enzyme. Bakers then add malt flour or fungal amylase to support fermentation and crust colour.
As an indicative trade practice, bread flours are often specified at 250 seconds or more, and values below about 200 seconds cause trouble in bread. Rye bread needs its own band.
How to use it in a contract
Name ISO 3093, the moisture basis and the minimum (plus a maximum for bread flour). Test every lot. The wheat flour specification guide shows how falling number fits with protein, gluten and ash, and the glossary entry on falling number gives the short definition.