Between the numerous species of linaceous plants, the linus usitatissimum or linseed is the most industrially used.
Next to its importance for the production of textiles, used since so many centuries, linseed is also an oil seed with specific uses.

We may distinct winter linseeds and summer ones. The producing countries are the USA, India, Russia, Canada, Mexico, Belgium and Holland. The most used varieties for the production of oil seeds are different from those used for textiles (which have a lower oil content).

Flax is an annual and fibrous plant with a single straight stem, with branches supporting flat leaves of elongated (3 to 6 cm) and narrow (1 cm) shape, and without petioles.

The textile type of flax may reach a height of 1.5 m while the species for oil production normally reach only 0.3 m.

The flowers are usually blue but you may find pink or white types, giving to linseed fields a nice coloured aspect.

The fruits are spherical or ovoid capsules and are located at the extremity of the branches; they contain usually about ten seeds. The seeds are flat, oval and pointed on one side; as an average, the are 5 mm long, 2 mm width and 1.5 mm thick; the weight is 4 to 8 mg. and the colour of the seed is brown.
The epidermis or external husk is covered with mucilage composed of carbohydrates that disperse in water to form a thick and gelatinous deposit (starch). When mature, the mucilage layer hardens and looses its gelatinous aspect.

The husk has a thickness of 0.2 to 0.4 mm and contains a certain amount of oil (7%) and of proteins (20%); the seeds are not decorticated.

The harvesting of linseeds is done in the same way as many other cereals.

The seeds have to be cleaned as usually a big amount of herbs (5 to 50%) are collected with the seeds. To store the seeds in safe conditions, it is necessary to dry them to a 10% maximum moisture and the ambient air moisture should be below 75%. Thus harvested seeds will be either directly processed or dried for storage.
Linseeds contain about 38 to 45% of oil and about 25% of proteins.
The seeds are first cracked on corrugated rolls, flaked and cooked before pre-pressing, and then after a new preparation by cracker (discs and corrugated), cooker and flaker, the cake is solvent extracted.

The oil from cold press is of light yellow colour and may be used theoretically as food . The ones from hot pressing and from solvent extraction are of dark brown colour and are used in industries of varnishes, paints, linoleum and soap.
The refining comprises degumming, bleaching, and fatty acid stripping steps.

• 45-58% of linolenic acid
  
• 13-16% of linoleic acid
  
• 17-26% of oleic acid
  
• 0.1-0.3% of palmitoleic acid
  
• 6-7% of palmitic acid
  
• 4.5-6.5% of stearic acid
  
• Iodine Value : 170-204
  
• saponification value : 188-196
  
• melting point : -20°C
  
• titer : 19-21°C
  
• unsaponifiables : 1.5%
  
• viscosity at 20°C : 46-50 cps
  

Linseed oil is the most well known siccative oil due to its very high percentage of linolenic acid. It has the property of absorbing the oxygen from ambient air and to form a solid but elastic material known as linoxyne. This property is of course used to prepare varnishes, paints and oxidised oils (see under rapeseed).

Linseeds contain a small percentage of a cyano-genous carbohydrate called LINAMARIN and one enzyme called LINASIS. At a temperature of 40-50°C and with moisture, the enzyme acts on the linamarin to release cyanhydric acid (HCN).
When the oil is cold press extracted, the linasis and the linamarin are not eliminated and may kill animals fed by this type of cakes.

The heat treatment in the cooker and in the press permits the elimination of toxic elements and thus cakes or meals are no longer dangerous for livestock feed; it is even an excellent feed as it contains 30-40% proteins and is easily digested.
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