Falling Number

A sample of ground grain is mixed with water in a viscometer tube and placed in a boiling-water bath. The mixture is stirred mechanically as it heats, which gelatinises the starch and forms a paste. At a defined point the stirrer is released and allowed to fall under its own weight through the paste; the falling number is the total elapsed time, from the start of stirring, for the stirrer to fall a fixed distance. A thinner paste offers less resistance and the stirrer falls faster; a thicker, more intact starch paste offers more resistance and the stirrer falls slower.

Alpha-amylase is the enzyme responsible for thinning the paste. Sound, undamaged grain has relatively little active alpha-amylase and forms a stiff paste. Grain in which alpha-amylase has become active — most commonly because the grain sprouted before or shortly after harvest, or matured late under wet conditions — forms a paste that thins rapidly as the enzyme breaks down starch molecules during the heating step itself.

The practical stake is bread and noodle quality. Alpha-amylase activity from pre-harvest sprouting or late-maturity conditions degrades starch within the dough during baking or processing, producing sticky, poorly structured bread crumb or gummy noodles, even when the grain looks visually sound. The falling number test exists specifically to catch this invisible starch damage before the grain reaches a mill or bakery.

The falling number is an inference from paste viscosity, not a direct enzyme assay. Anything else that changes how the starch paste behaves under heat will also move the number, whether or not alpha-amylase activity has actually changed. Starch that has been mechanically damaged — by harsh milling, dehulling, or over-aggressive drying — pastes differently than intact starch. The fineness to which the sample was ground before testing also affects how quickly and evenly the paste forms.

• Falling number is not a direct alpha-amylase assay; it infers enzyme activity from paste viscosity and can be moved by non-enzymatic factors.
• It is not a general soundness or quality index and does not substitute for testing protein, moisture, or foreign material separately.
• It is not a protein or gluten strength measure, even on wheat destined for baking.
• It is typically a contract or specification factor negotiated between buyer and seller, not a numbered factor in every commodity grading schedule.

Because the falling number test relies on precise timing of a physical event in a heated liquid, it is sensitive to details of execution. Sample grinding fineness, sample moisture, and instrument calibration all influence the result and must be controlled for results to be comparable between laboratories or over time. Altitude introduces a further, less obvious effect: the test runs the sample at the boiling point of water, and boiling point falls as elevation rises, so a test run at high elevation reaches a lower temperature than the same test at sea level under otherwise identical conditions. Laboratories operating at altitude apply a documented correction for this effect; results from different elevations should not be compared without accounting for it.