Sprouting grain puts a dampener on quality

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Australian Export Grains Innovation Centre grain quality specialist Dr Ken Quail examines the importance of grain soundness and how it affects the quality of end products

Close-up photo of sprouted wheat
Sprouted wheat. Photo: Evan Collis

‘Sound’ is a term used to describe grain that is free of sprout damage. The falling number test is used to determine whether grain is sprout-damaged or not.

Wet conditions just prior to or at harvest can result in grain that has sprouted (also known as ‘shot or ‘sprung’ grain). This is also referred to as pre-harvest sprouting. The degree of sprouting depends on the duration and number of rain events and the conditions immediately after the rain.

Sprout-damaged grain has a severe impact on end-product quality, which is why it is so important to test at grain-receival depots. Nonetheless, Australia has an excellent reputation for the supply of sound grain that meets customer requirements for bread, noodles and malting.

What is the impact on end-product quality?

Bread

Sprout-damaged flour makes it almost impossible to bake good bread. Sprouting results in high levels of an enzyme called alpha-amylase, which converts starch to sugars. This results in bread dough becoming sticky and difficult to process. During baking, wheat starch gelatinises which, in combination with protein, forms the bread ‘crumb’. If too much of the starch has been converted to sugars, a sticky gel forms an unacceptable crumb that will stick to the slicer blades in a bread production line. In addition, sprout damage can reduce the quality of protein, which affects dough strength and extensibility (stretchiness). All of this results in poor-quality, sticky and low-volume bread.

Noodles and pasta

At least one-third of all Australian wheat exports are used in the production of Asian noodles. Noodle consumers can be very demanding in their expectations, so it is critical to ensure Asian flour millers have access to the highest-quality Australian grain.

Noodles are highly sensitive to the impact of sprout-damaged wheat. During sprouting, a range of enzymes other than alpha-amylase are also released and these contribute to darkening reactions when making noodles. This results in dull noodles with brown to green colours that Asian consumers find highly undesirable. Asian customers typically prefer bright noodles with a white to yellow appearance (depending on the specific market and noodle type).

Severe sprout damage also affects noodle texture, resulting in undesirable ‘mushy’ noodles. Other effects such as increased cooking loss are also undesirable. The impact of sprout damage on durum wheat used to produce pasta is similar to the effects observed in Asian noodles.

Malting barley

Malted barley is produced using a controlled sprouting process to release the sugars required for beer brewing and other products.

Barley that has already started sprouting due to rain at harvest is not suitable for processing because it negatively affects malt consistency and yield. When rain events cause pre-harvest sprouting, the impact is highly variable between individual grains, depending on their exposure in the crop canopy. This results in inconsistent and unacceptable malting performance.

Canola oil

Sprouted canola seeds return lower oil yields during processing.

Feed grain

Severely sprouted grain is typically graded as stockfeed. If the grain is not severely affected by fungi and mould, and is free of mycotoxins, the sprout damage can actually be considered an advantage. The release of enzymes due to sprouting has been shown to raise the metabolisable energy for poultry and pigs.

What is the Falling Number test?

The falling number test has been in use for more than 50 years and is the international trading standard for measurement of sprout damage.

The test imitates how flour might behave in a bakery. It measures the amount of time, in seconds, it takes for a plunger to fall to the bottom of a glass tube that is filled with a heated paste of wheat meal and water. The time taken for the plunger to fall is known as the falling number. High-quality wheat makes a thick paste that slows the passage of the plunger resulting in falling number values of more than 300 seconds.

When sprouting has occurred, even if it is not visible in the grain, the release of alpha-amylase will break the starch into sugars, resulting in a sweet liquid that does not resist the fall of the plunger, which results in falling numbers below 200 seconds.

What can I do about it?

Multiple rain events close to harvest, accompanied by slow drying conditions, are likely to result in sprout damage. When this occurs, there is little that can be done. If there is a risk of rain events, harvesting before the rain is possibly the only way to avoid sprouting. This may require harvesting at high moisture levels, which must be supported by a strategy to dry the grain below 12.5 per cent for safe storage.

Blending is not recommended as a method of reducing the impact of sprout damage when grain is to be graded. Blending sprouted grain is generally a good way to spoil good-quality grain. If you are producing grain in a region with a higher risk of rain at harvest, harvest and store any grain that might be at risk of sprouting separately from sound grain, and consult your seed supplier to identify varieties that are less susceptible to sprouting.

GRDC research projects UA00130, UA00150, CFF00003 have delivered pre-harvest sprouting control options to breeders.  o

GRDC Research Code AEG00006

More information:

Dr Ken Quail
02 8025 3200