Winterization is a core step in producing commercially viable cannabis extracts . After decarboxylation and extraction, winterization purifies crude extract to increase its quality and value. The process removes lipids, which are fatty acids that cause an extract to be waxier, softer, and cloudier. The melting point of lipids is higher than the extract, which can cause a harsh and diminished flavor; without removal, the product is less pure.
So what is winterization? In a nutshell, winterization dissolves extract oil (non-polar) into ethanol or another solvent (polar) and places the solution in extreme sub-zero temperatures. Since lipids have lower solubility in the sub-zero solvent (e.g., ethanol), they will float to the top of the solution like oil in an oil and vinegar salad dressing . Once they’ve separated and floated to the top, they can be filtered out.
The process consists of two major steps:
- Winterization: Dissolve crude extract (e.g, BHO) in a solvent such as isopropanol or ethanol, and chill in a sub-zero freezer. The amount of time and precise temperature are variable depending on the solvent and procedure. Manufacturers may implement patented and secretive techniques . Temperatures of -20 to -80°Celsius for 24-48 hours are normal [2,3].
- Filtration: When the lipids have precipitated to the surface of the solution (like floating wax), filtration can commence. Tools in this process include vacuums and pumps that send the solution through several layers of filters. Metal micro-filters can be used [2,3], but paper filters are also used.
The solvent will then be evaporated, and voila! The manufacturer is left with an extract that is virtually free of lipids. The final product is more stable and pure. It can therefore be stored for longer periods of time and is more pleasing to the consumer.
- Puri, Pushpinder S. “Winterization of Oils and Fats.” Journal of the American Oil Chemists Society. 1980,Volume 57(11): A848–A850. doi:10.1007/bf02687675.[Times cited = 8. Journal impact factor=1.541]
- Bjorncrantz, W.“Winterized Crude Cannabis Extracts and Methods of Preparation and Use.” United States Patent 20150105455. 2015.
- Aggarwal, Sunil. “Cannabis: A Commonwealth Medicinal Plant, Long Suppressed, Now at Risk of Monopolization.”Denver University Law Review. 2010, 88.Times cited = 8.