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Maceration, or infused oils have been used since antiquity and was most likely the first process used to capture scent. Not only the aromatics are recovered in this process, but other plant constituents useful in herbalism. In this process, plant material is chopped or crushed to open up the cell walls, placed firmly (but not too tight) into a vessel, and covered with vegetable oil to infuse plant constituents into the fixed oil. The oil can be 'cold infused' and left at room temperature for several weeks (up to a month or so), or heated to a very low temperature (not to exceed 100-105 degrees F) for a shorter duration, sometimes in a crock pot, 5-7 days. Many different fixed oils are used, including fractionated coconut oil which will not go rancid and greatly extends the shelf life of your finished product. Olive oil is probably the best oil for maceration, is relatively stable and, if refrigerated, has a reasonable shelf life. After the maceration period, remove all plant material. You may want to use a tincture press when infusing with dried plant material. Some plants are infused fresh, producing the most efficacious product, such as Calendula flowers, Chickweed, St. Johns Wort and Arnica. Fresh plants contain water, so care must be used to insure all water is removed from the finished product or it will mold and go rancid. One should 'rest' or partially dry fresh plant material for 24-48 hours prior to infusing. After the maceration is complete, remove fresh plant material without squeezing or pressing so as to not leave any more water behind than necessary. Leave the infused oil open for a day or two to evaporate off some water. It is best to siphon the oil off the top and leave a half inch or so of oil in the bottom, which will contain the water that settles. Do not agitate your vessel during evaporation period as you want all water to remain at the bottom. Dried plants can be infused in the same manner and the oil will not contain water.
(See also alcohol extractions)