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Choosing the Right Screens
A sieve is a utensil that is comprised of a wire or plastic mesh held in a frame. A sieve can be used to strain solids from liquids, for reducing soft solids to a pulp, e.g., creating a puree and for grading, i.e., separating coarse particles from finer particles.
It is the ability to grade a product that attracts those who want to produce kief to use a sieve. Cannabis trim, i.e., the cannabis material left over after the removal of the buds from the cannabis plant, contains cannabinoids and terpenes, although less by weight than that contained in buds. Those in the cannabis industry have come to realize that if they just throw away or compost the trim instead of using it to make hash, edibles, etc., they are missing out on a huge amount of value.
The cannabinoids and terpenes (trichomes) that are located on the trim vary in size from 25 to 220 microns. However, it is generally agreed that any particle above 160 microns has a lot of plant matter, as well as anything below 38 microns. The reason anything above 160 micron in size is usually discarded is because plant matter is generally larger than trichome heads, while anything smaller than 38 microns is probably particulate matter or broken trichome pieces.
A screen having a micron size of 70+/- is usually produces the highest quality product. However, going from a 160 micron screen to a 70 micron screen does not product the highest quality product. Using a series of screens, e.g., 160 to 120 to 90 to 70 will result in a much cleaner final product in the 70 micron bag, and also in the other higher micron bags. In most cases excellent results can be obtained using a set of three screens.
Robert Clarke in his book Hashish grades screens, as follows:
150 microns – very large plant debris
130 microns – very large trichomes
110 microns – large trichomes
90 microns – medium size trichome
70 microns – small trichomes and debris
50 microns – very small debris and little trichomes
below 50 microns – vary small dust and debris
When making hash the screen sizes can vary from about 65 microns to 125 microns. If the particles are larger than 125 microns they are usually not very potent. Potency increases as the particle size decreases to 65 microns. At about 65 microns the trichome particles are considered to be optimal.
Although the above is a good general guideline, certain strains have plenty of smaller headed and larger headed trichomes, which can call for using a screen size as high as 120 microns and as low as 38 microns. Learning the specifics of the strain you are going to grade can help a person produce the highest quality product.