Aug 03 2007
Harvesting rapeseed: black seeds for golden oil
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Early August and the harvest of the winter sown oilseed rape (Brassica napus, its edible varieties also known as canola) is well underway in the UK. The spring-sown crop ripens later and will be ready for harvest in late August and September.
From Spring Yellow to Harvest Brown
Rapeseed ready for harvest is a drab brown, a far cry from the bright yellow fields of the crop in flower, and often has a distinct cabbage smell, a reminder that it’s a member of the Brassica family.
Spring-sown rape ripens unevenly and must generally be dessicated or swathed a week or two before harvesting to ensure ripeness of all the seedpods. Both methods kill the plants to allow ripening to continue without further growth or maturation - dessication is achieved by chemical means (generally Diquat spray), swathing is a mechanical alternative.
Rape is combine harvested to yield its tiny black seeds, destined to be crushed to produce oil for food, industrial uses and, increasingly, biofuels. A growing number of farmers are cold pressing the seeds themselves to produce extra-virgin rapeseed oil. The meal left after crushing is high in protein and used for animal feed.
(The increasing use of rapeseed for biofuels is worrying in the context of now rising food prices. Rapeseed biofuel is certainly not the green panacea it’s sometimes claimed to be - Peak Energy calculates that even if all the world’s arable land were used to produce rapeseed for biofuels, it would only provide enough to replace a third of our current oil requirements.)
A New Crop
Oilseed rape is a relatively new crop and has been grown on a commercial scale in the UK for only 30 years. It’s increasingly popular with farmers, fitting in well with cereal production. As a brassica it doesn’t share pests and diseases with cereals so makes an ideal break crop in cereal rotations, while it can be grown with the same machinery. According to the DEFRA annual farm survey, just over 220,000 hectares of rapeseed were grown in 1983, rising to over 500,000 in 2005.
Edible Varieties
Edible varieties (without the toxic erucic acid) were developed in the 1970s through conventional breeding, not genetic modification. GM varieties are now available though not grown in the UK and unlikely to be so until at least 2009 (according to DEFRA). Edible rapeseed is sometimes referred to as LEAR (Low Erucic Acid Rapeseed) or Canola (Canadian Oil Low Acid).
We’re used to seeing extensive fields of yellow rape in flower in the spring, but the previously obscure uses of this crop are suddenly coming into the public eye. From debate about the merits of rapeseed biofuels to cold-pressed rapeseed oil on the supermarket shelves, we’ll be seeing a lot more of it.
A Rapeseed Reading List
