Rain, rain, go away. Come again next Anzac Day…..
Well, rain is still falling across most of the growing regions in SA as crops mature and we begin the 2022 harvest. And unfortunately, when mature cereal crops receive enough rain before harvest, sprouting becomes a severe threat to grain quality. Germination of grains increases the enzyme that breaks down starch, which is essential for end products such as millers producing good-quality flour. (See image below). Sprouted malt barley grains are also rendered useless because the malting process at breweries requires grain germination to form malt.
Falling numbers is a standard grain test conducted at receival sites to determine whether grain has sprouted and how it will affect the malting or milling ability. It is an internationally recognised quality indicator accepted by both buyers and their customers. The test measures the amount of time a plunger takes to fall through a mix of heated-up ground-up grains and water. (See below)
When starch is mixed with water and heated up, it forms a thick paste, so the plunger takes time to fall. When sprouted grains are in the sample, more of the starch has already been broken down by enzymes and turned into sugar, so when sugar is mixed with water and heated up, it forms a sweet, thinner liquid which the plunger falls through faster. Hence, when sprouted grains are present in the sample, the falling number test will be lower, meaning a possible downgrade. The acceptable limit for hard wheat and malt barley is 300 seconds for the plunger to fall to the bottom.
However, there are some criticisms. And the test often causes frustration and confusion for growers because different samples have very different results. It’s important to remember the falling number test was designed to be conducted in a laboratory and isn’t very accurate in the field where high volumes of samples are tested under time constraints. A few things can cause variables at receival sites, such as the cleanliness of the glass tubes and plungers and possible cross-contamination. Also, technically the weight of the sample used for the test should be adjusted according to the sample moisture content – but it isn’t because, again, there are time constraints. Distilled water at a constant temperature of 20˚C should be used, which isn’t viable at receival sites. And finally, sampling errors are significant – the inclusion or exclusion of a few individual sprouted grains in the test sample can hugely affect the result. The accuracy for a value of 300 seconds is +/- 30 seconds. Meaning for the same sample, you may get a result of 330 or 270 seconds – a massive difference in terms of grain receival standards.
It’s crucially important to understand you can request a second test if the first falls below 300 seconds.
If a crop is weather damaged and you are downgraded on falling numbers, there is also the option to try and blend good and bad grain. However, this is risky, as you could downgrade the whole lot. It’s tricky. When blending grain for falling numbers, equal loads that had results of 400 and 200 seconds would give a best possible falling number of 260 seconds – not 300 seconds. Due to this, getting blending right will often take a lot of trial and error. But in a year like this, when the price difference between high and low-quality grain is significant, it can certainly pay off.
There’s a lot of great information on Grain Growers Falling Numbers Fact sheet, which you can find here: https://www.graingrowers.com.au/news/falling-numbers-guide-2021