Recent summer rainfall has stalled harvest and germinated more weeds but it has brought some positivity by providing an opportunity to capture and store soil moisture for the 2018 season. Unharvested wheat and barley grain quality may begin to germinate, or sprout, in the head.
Germination causes an increase in alpha-amylase, an enzyme that breaks down starch. The longer the grain sprouts, the greater the amount of alpha-amylase formed.
Grain with high levels of alpha-amylase produces lower quality flour and products made from the flour. Examples include sticky, doughy bread which won’t slice in mechanical slicers, or noodles which are too stretchy, and slip from the wooden rods where they are draped to dry. The level and impact of damage due to germination is not fully realised until it is processed into bread or pasta.
The most effective way of measuring the amount of alpha-amylase present is to use the ‘falling number’ method. The falling number test often causes frustration and confusion for growers because it does not directly measure amylase enzyme activity, but measures changes in the physical properties of the starch portion of the wheat kernel caused by these enzymes.
The test uses an instrument measuring the time for a plunger to fall to the bottom of a glass tube filled with a heated paste of wheat-meal and water. The time taken in seconds is known as the falling number. Wheat that is unaffected by germination makes a thicker paste increasing the amount of time for the plunger to fall, giving a larger falling number. A smaller falling number is associated with greater sprout damage ie. the quicker the plunger falls because the paste is less viscous (or sticky). A value of 300 seconds is a critical value for both wheat and barley (Table 1).
Table 1. Minimum falling number required for Australian wheat grades.
| Grade | Falling Number Minimum (seconds) |
| APH1 and HPH2 | 350 |
| H1, H2, APW1, APW2, ASW1, ANW1, ANW2, ASWS, APWN, DR1, DR2, SFE1, SFT1, SFE2 and SFT2 | 300 |
| AUH2, AUW1, HPS1, AUN1, SGP1 and SGP2 | 250 |
| AGP1 and DR3 | 200 |
Source: GrainCorp, wheat standards 2017-2018.
For malting barley, the minimum falling number required is 300 seconds while there is no minimum for feed barley.
It is not recommended to blend falling number qualities and storing such grain. If there is no other option to store, growers need to be mindful of the increased risk of insect and fungal damage and mould growth.
BCG is not providing this information as a recommendation to store grain but to enable more informed decisions. Grain markets are volatile and can fluctuate significantly and the decision to store grain could impact on grain quality.
Disclaimer: This publication is provided to you by way of general information only. Birchip Cropping Group Inc. (“BCG”) does not warrant the accuracy of the contents of this publication or of the applicability of the information to your circumstances. BCG excludes all liability (including liability in negligence) in relation to the information contained in this publication and for any consequences arising from its use.
