A Glimpse into Tradition
Known as 'chekku' or 'kolhu' in different parts of India, the wooden ghani is a testament to timeless engineering. It consists of a large, fixed wooden mortar and a revolving wooden pestle that crushes oilseeds. For centuries, this pestle was turned by
bullocks walking in a slow, steady circle; today, a slow-speed motor often performs the same task. The process is deliberately unhurried, focusing on gentle pressure rather than speed. This isn't just about nostalgia; it’s a method designed to extract oil in its purest form, without introducing the stressors of modern industrial processing.
The Science of Spoilage: Oxidation
To appreciate the ghani's genius, we first need to understand the enemy: oxidation. When edible oils are exposed to heat and oxygen, their chemical structure begins to break down. This process, known as lipid oxidation, creates harmful free radicals and causes the oil to become rancid. Not only does this spoil the taste and aroma, but it also destroys the valuable nutrients that make sesame oil so beneficial, such as its natural antioxidants and healthy fatty acids. High heat, a common feature of industrial oil extraction, dramatically accelerates this damaging process.
Wood: The Natural Heat Shield
This is where the 'wooden' part of the wooden ghani becomes critical. Unlike metal presses that conduct and retain heat from friction, wood is a poor conductor of heat. As the pestle rotates and crushes the sesame seeds, the friction generates a small amount of heat. However, the wooden mortar naturally absorbs and disperses this warmth, preventing it from building up and 'cooking' the oil. This keeps the temperature during extraction remarkably low, often staying below 45-50°C. This simple material choice is a key factor in what makes this method a true cold-pressing technique.
The Virtue of a Slow Pace
The second safeguard is speed, or rather, the lack of it. The wooden ghani operates at a very low RPM (revolutions per minute). This slow, grinding action minimizes friction, which is the primary source of heat in any mechanical press. Industrial expellers, which are designed for maximum yield and speed, can generate temperatures exceeding 100°C, essentially frying the oil as it's extracted. By keeping the process slow and cool, the ghani method significantly reduces the risk of thermal degradation and oxidation, ensuring the oil remains as close to its natural state as possible.
Preserving Nature's Goodness
The result of this low-heat, low-oxidation process is an oil that is nutritionally superior. Sesame oil is naturally rich in antioxidants like sesamol, sesamin, and Vitamin E, which have powerful anti-inflammatory properties. These delicate compounds are thermolabile, meaning they are easily destroyed by heat. The gentle nature of wooden-ghani extraction protects these nutrients, along with the oil's polyunsaturated fatty acids. The final product is not just an oil but a wholesome food, retaining the authentic flavour, rich aroma, and the full spectrum of health benefits that nature intended.
