You're so right about some plants just bursting with scent. All you have to do is brush up against a rosemary bush, or rub a few mint leaves together to release their scent. But other plants are not so generous with their scented oil. It takes 2000-5000 pounds of rose petals to yield one pound of rose essential oil. It takes 1000 pounds of jasmine (about 3 million flowers) to yield a pound of jasmine essential oil. Compared to these, lavender seems like a bargain! Only 200 pounds of flowers to make a pound of lavender essential oil.
The majority of essential oils are obtained through two methods: distillation and expression.
Expression works for citrus oils like orange, lemon and lime (the rind is pressed, squeezing the oil out), but the majority of the rest of the essential oils come from some sort of distillation either water or steam.
There are also some rarer plants that need to have their essential oils solvent extracted - these are usually referred to as concretes, resinoids or absolutes.
But steam is the key to most of the essential oils that we work with as candle and soap makers. Here's more information about water and steam distillation of essential oils.
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