The percentage of flax grading Canada #1 is frequently very high, but dockage is often up to 10%. Dockage can be reduced by controlling broadleaf weeds as well as grassy weeds - including volunteer cereals. If green weed seeds are present, they may raise the moisture of the flax seeds enough to cause heating and moulding. Removing this dockage before putting the flax into long-term storage is advisable.

Storage of Flax Seed

Sample of No. 1 Canada flaxseed (magnified)

Sample of No. 2 Canada flaxseed with rime and scabbing from a wet harvest

Heated flax
Stored flax requires more attention than does stored wheat. Freshly harvested seed can maintain a high respiration rate for up to six weeks before becoming dormant. This, coupled with mould growth if the relative humidity of the air in the spaces between the seeds rises above 70%, can lead to heating. Once flax starts heating in a pocket, the heat will spread quickly - possibly throughout the entire bin. For this reason, flaxseed should be cooled down after it is put into storage.

Flaxseed can be safely stored at seed moisture levels of 10% or lower. Tough flaxseed contains from 10.1 to 13.5% moisture; damp flaxseed is over 13.5% moisture (Canadian Grain Commission, Official Grain Grading Guide, effective August 1990).

Each year some heated flaxseed shows up in the delivery system. A wet harvest or an early fall frost will increase the percentage of heated flax. If aeration equipment is not available, bins of flaxseed should be inspected frequently for problem spots until the seed has cooled down. Flaxseed has an airflow resistance very similar to Polish- type canola (B. campestris). Periodic checking is necessary to detect the development of hot spots.

As in other oilseeds and cereal grains, moisture migration will occur in stored flaxseed. Even though the seed is binned with uniform moisture, high moisture spots can develop by moisture migration. This usually happens in fall and early winter, although it can also occur in the spring.

Heated to binburnt flaxseed

Storage insects
Stored flaxseed is not troubled by storage insects as frequently as cereal grains. Insects that can occur in stored flax are: saw-toothed grain beetle, confused flour beetle, merchant grain beetle and red flour beetle. Various fungus beetles and numerous mites can be found in seed that remains tough to damp in storage. Research in Manitoba has revealed that flax varieties vary in their susceptibility to the saw-toothed grain beetle. The rusty grain beetle occurs occasionally in carlots of flax. However, it is suspected that this insect feeds on cereal admixtures in the flax.

The optimum temperature for rapid growth of insects is in the range of 30° to 35°C (86° to 95°F). Their activity is greatly retarded by temperature below 18°C (64°F). If the grain is cool and dry, insects will generally not thrive. However, flax may be put into storage at an acceptable moisture content and temperature, but pockets of high moisture and temperature can develop later through moisture movement on convection currents and heat production by mould respiration which would encourage insect activity.

Solin
The Canadian Grain Commission has established official grade tables for solin which are different than those for flax. It is important that admixtures of canola, mustard and especially flax are avoided during production, storage and transportation of solin. There are three main differences between flax grade tables and solin grade tables: For solin there are:

tighter limits on damaged seed;
more categories for inseparable seed;
slightly tighter limits for heated seed.

Adapted from Growing Flax published by the Flax Council of Canada The contents of this page are no longer available.

For more information about the content of this document, contact Murray Hartman.
This document is maintained by Stacey Tames.
This information published to the web on June 25, 2001.