Linseed oil can be produced in different ways. For pharmaceutical purposes, the flaxseeds are pressed purely mechanically in a cold-press process (cold pressing). For this, the mature and (depending upon the type of press) crushed or whole flax seeds are de-oiled using a press. The oil yield depends on the throughput and on the temperature. In the type of pressing, the oil reaches a maximum temperature of 40°C. Before usage, however, the solids must be removed. This is achieved through various purification levels, depending upon the oil mill. First of all, the unpurified oil is roughly purified and then finely filtered. A safety filtration concludes the purification process. All of these purification levels are carried out efficiently. As an alternative purification system, the solids are left in storage long enough for them to settle, and then are removed through decantation. For technical purposes, on the other hand, a hot pressing is used. To this end, the flaxseeds are first pre-warmed or pre-heated, then while warm, pressed in a screw press. This allows the seeds to be pressed to the highest degree. The press cakes can also increase the oil yield by undergoing extraction with a solvent. Since linseed oil obtained in this way still contains mucilaginous and sulphuric substances, the oil must subsequently be refined.
There are two additional types of linseed oil: the sun-thickened type and the blown type. The former is placed in a long, flat vat, which is important to achieve the largest possible area for oxidation, and then placed in the sun, whereby it must be stirred regularly to prevent film from forming. For the latter, an aerator is used; constant circulation prevents the formation of film. The advantages of these two production methods is that the oil consistency becomes thicker and the volume hardly increases while drying (which reduces the risk of wrinkles and cracks); and that the linseed oil becomes lighter (through bleaching) and the drying time shorter. These two special types of linseed oil are used in painting, especially in Flemish baroque painting, as well as in violin making.
Characteristics and shelf life
Depending upon the method of production, cold-pressed linseed oil is a gold-yellow color, while warm-pressed linseed oil is more of a yellowish brown. A light to golden yellow color, however, characterizes refined linseed oil. The oil has the scent of pyrazine, and smells slightly roasted and tangy, like hay, while being described as herbaceous to musty, and possibly giving off fishy notes. Taste-wise it is reminiscent of freshly cut grass, tasting freshly and faintly nutty and hay-like, yet after being stored, it tastes increasingly bitter and prickly. Owing to its high degree of atomization, linseed oil tends toward spontaneous combustion at room temperature, yet nevertheless has a flash point around 315°C and a boiling point of over 350°C, making it rather difficult to ignite. The melting point lies around-16 to -20°C. Linseed oil contains more than 90% unsaturated fatty acids, of which the portion of omega-3 fatty acids, those of α-linoleic acid, is about 45 to 71%. Additionally present in the oil are oleic acid (around 17-23.5%) and omega-6 linoleic acid (around 12-24%), as well as many vitamins and a relatively high mineral and Vitamin E content.
Since linseed oil is very sensitive to air, it develops a bitter taste after even a short time and becomes rancid quickly. After being opened, it should be stored in a cool place. Yet even in the refrigerator (around 4°C), it starts to develop a somewhat bitter taste and stays fresh a maximum of two months. However, due to linseed oil’s low melting point, it can also be stored in the freezer without turning solid. Here it stays fresh and its flavor unchanged for a number of weeks. All linseed products should be stored in dark, airtight containers.
Pharmaceutical and medical uses
According to the Lexikon der pflanzlichen Fette und Öle (lexicon of plant fats and oils) and Markus Hartmann’s Öle – natürlich kaltgepresst (oils – naturally cold-pressed), linseed oil possesses several beneficial characteristics. Because of its high linoleic content, linseed oil helps lower lipid levels. It can also lower elevated cholesterol levels and decrease blood pressure, thereby reducing the excretion of sodium in the urine. Additionally it has an anti-bacterial effect; can strengthen the vascular system, avert harmful plaque deposits, and prevent blood clots from forming. Linseed oil is also used in the production of ointments, wound powder, natural soaps, and viscous liniments.
Linseed oil is used in technical chemistry, where it is used as a raw material in the manufacture of oil paints, oil lacquers, and linoleum; and, on a smaller scale, also in the preparation of soft soaps, cement, printer’s ink, and liniments. Beyond this, it can also be used as a paint binder since it has a polymerizing quality. A further area of application for this oil is waterproofing. Linseed oil possesses water-resistant characteristics, yet at the same time also diffuses moisture, which makes it suitable for outdoor use in inclement weather. It forms a wax-like coating and is thereby ideal for waterproofing wood, plaster, masonry, and external facades. Furthermore, linseed oil serves as an additive, finding application in the manufacture of liners, packaging, polishes, lubricants, oilcloths, and pyrotechnical products. It is also mixed into latex paints to increase its adhesiveness. In addition, epoxy-enhanced linseed oil is also used as a stabilizer and/or in the shaping of vinyl-based plastics.
In the kitchen
Because of its particular flavor and since it is not very resistant to oxidation, linseed oil is not widely used in the kitchen. In India, however, it is commonly used for cooking and frying. Otherwise it is used in combination with mustard seed oil, peanut oil, or coconut oil. In Lusatia especially and in Silesia, this oil is used in foods containing milk, such as quark with potatoes, cucumber salad or sour herring in cream sauce. The layer of oil keeps the foods with dairy from becoming sour too quickly, which is especially practical during the summertime. Beyond this, linseed oil can also be used in vegetable dishes and with crudités.
In folk medicine
Because linseed oil supports cell regeneration, compresses with linseed oil have a softening and pain-relieving effect, and also help with painful, cracked skin, burns, and damaged skin.
In veterinary medicine
Animal food containing linseed oil not only has a beneficial effect on the digestion of dogs and horses, but also can cause their coats to shine. Because of its digestion-promoting effect, linseed oil is often used as a laxative for sheep and horses.
The press cakes (flax cakes) residual from the pressing are fed to livestock or used in fertilizer.
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In addition to their own knowledge acquired through press trials, the following sources were used to create the article:
- Öle, natürlich kaltgepresst, Basiswissen & Rezepte, Marcus Hartmann, Hädecke, 2008
- Heilende Öle, Pflanzenöle als Nahrungs- und Heilmittel, Neue Erkenntnisse, Günter Albert Ulmer Verlag Tuningen
- Lexikon der pflanzlichen Fette und Öle, Krist, Buchbauer, Klausberger, SpringerWienNewYork, 2008