Written by:

Simon Leake | Agronomy | 0439 999 173

There has been substantial late season rainfall around the state this year leading to grain quality issues including sprouting in wheat and barley which is measured through the ‘falling number’ test. This article is a refresher on this quality issue and the test specifically.

Falling numbers refers to the test that is used to check the quality of sprouted or rain affected grains. When rain falls on a mature crop it induces germination which lowers the quality of the grain. It lowers the quality of the grain because when germination is induced it stimulates the synthesis of alpha-amylase which is an enzyme that breaks down starch (as used as energy to get a seedling out of the ground). Low starch correlates with higher alpha-amylase and grains with higher levels of alpha-amylase produce lower quality flour. It’s called the falling number test because of the way it is conducted.

Basically, the grains are crushed and mixed with warm water to make slurry, a plunger is then dropped into the solution and then timed for how long it takes for it to reach the bottom of the solution, this gives the falling number reading in seconds. The higher the falling number the better because the longer it takes to fall correlates with how much starch (or lack thereof) is contained in the grain, when there is less starch this decreases the falling number/quality of the grain. As you can imagine the more starch there is in the grain the more viscous the solution will be and the longer it will take for the plunger to make it the bottom. In essence the falling number test replicates the baking process because lower levels of starch will produce lower quality flour and therefore a lower quality final product. Ideally, we want to keep our falling numbers above 300 seconds. CBH standards can be seen below in Table 1.

Table 1. CBH receival standards for falling numbers and sprouted grains (CBH, 2022).

So, we now know what falling numbers means but what causes the underlying issue? It’s caused by a combination of variety susceptibility, rainfall (obviously) and the level of maturity of the crop. Rainfall leading up to maturity can also increase the susceptibility to more rain later. The more rainfall and rainfall events closer to harvest the worse the impact on falling numbers depending on the variety. DPIRD has also come up with a rating system for the susceptibility of different varieties to falling number issues, this can be seen in Table 2 below. Use this table for variety selection and for planning around harvest. If you’re in higher rainfall areas or high harvest rain risk areas, it would make sense to avoid varieties with low falling number rating. Trouble is, sometimes the best yielding variety in an area might be one with a low rating, like Rockstar in Kojonup. If that were the case, it would still be worth considering for a percentage of your wheat program. If you harvest that low falling number variety first or even switch to wheat before finishing the barley this would considerably reduce your chances of getting rain exposure and still realise your higher yield potential from that variety.

Table 2. Falling number index rating for common wheat varieties grown in Western Australia, the higher the number the less susceptible to low falling numbers on a 1-9 scale, p indicates provisional (DPIRD, 2022).

If you’re exposed to rain during harvest and are at risk of having falling number issues, there are a few things worth considering:

• Falling number tests aren’t that accurate – given the variability of samples and testing conditions results of a test on the same sample won’t always be the same. Estimates suggest there could be around 30 second’s range above or below a given result. So, if your sample is only slightly under 300 seconds it would be worth getting it retested to save it getting downgraded and gain a few dollars.
• Blending can get you out of trouble – blending low falling numbered grain with higher falling numbered grain can give you a sample that is acceptable however adding say half low falling number grain and half acceptable falling number grain won’t always average out the way you expect it so will have to run with guess and check to see what works, maybe start less low falling numbers percentage and work back from there.
• Falling numbers isn’t tested at all CBH sites – only higher risk areas are tested and not all samples are tested – only when sprouted grains are observed.
• Variety choice – as mentioned above, if situated in a high-risk environment it’s better to allocate a larger portion of a wheat program to a variety with a higher falling numbers rating.
• Harvest plan – aim to harvest lower falling number rated varieties as a priority, like Vixen and Rockstar.
• Harvest output – greater harvest efficiency will reduce your risk of exposure to rain – think longer shifts on the header, bigger headers and reducing bottlenecks etc

If you’re exposed to rain during harvest and are at risk of having falling number issues, there are a few things worth considering:

• Falling number tests aren’t that accurate – given the variability of samples and testing conditions results of a test on the same sample won’t always be the same. Estimates suggest there could be around 30 second’s range above or below a given result. So, if your sample is only slightly under 300 seconds it would be worth getting it retested to save it getting downgraded and gain a few dollars.
• Blending can get you out of trouble – blending low falling numbered grain with higher falling numbered grain can give you a sample that is acceptable however adding say half low falling number grain and half acceptable falling number grain won’t always average out the way you expect it so will have to run with guess and check to see what works, maybe start less low falling numbers percentageand work back from there.
• Falling numbers isn’t tested at all CBH sites – only higher risk areas are tested and not all samples are tested – only when sprouted grains are observed.
• Variety choice – as mentioned above, if situated in a high-risk environment it’s better to allocate a larger portion of a wheat program to a variety with a higher falling numbers rating.
• Harvest plan – aim to harvest lower falling number rated varieties as a priority, like Vixen and Rockstar.
• Harvest output – greater harvest efficiency will reduce your risk of exposure to rain – think longer shifts on the header, bigger headers and reducing bottlenecks etc