When it comes to solventless extraction, trichome head size can play in role in the end product and the overall experience of the consumer. Trichomes are external extensions that appear on the leaves, stems, bracts, and blooms of many plants and not just cannabis. These extensions often look like hairs, glands, or bulbs covering different parts of the plant. They develop into the treasured resin-producing-and-excreting components of cannabis that hold a plethora of desirable cannabinoids.
The three different types of trichomes that secrete cannabinoids are capitate-sessile, capitate-stalked, and bulbous.  Desirable cannabinoids and terpenes accumulate in the trichome heads of the capitate-stalked and capitate-sessile trichomes.  The process of collecting these trichome heads has existed since cannabis was first cultivated and can be done without solvents via dry sieving or through ice water agitation, commonly known as bubble hash.
Common collection methods of trichome heads use a series of micron filters to sieve the different-sized heads away from other plant matter according to size. This extracts a high-grade accumulation of resin glands to develop into hashish, which can be inhaled or included in the production of other cannabis-infused products. Frenchy Cannoli, a well-respected hashishin, recommends a sieving set up that includes bags of 220, 190, 160, and 45 microns.
Capitate-stalked trichomes are the most highly sought-after type in cannabis and are found in the flowers and leaves of the plant during its flowering cycle. These are also the largest trichomes, ranging in height from 150-500 microns, and accumulate the greatest quantity of THCA/CBDA.  These heads are the most desirable for top quality hash.
[Graphic 2: Andre C.M. et al (2016). D is a capitate stalked trichome; C is a capitate sessile trichome; E is a bulbous trichome.]
Capitate-sessile trichomes range from 25-100 microns in diameter (with a single-cell stalk) and secrete fewer cannabinoids overall than capitate-stalked trichomes. These smaller capitate-sessile trichomes may be more suitable for edibles and other products intended for cannabis infusion.
Bulbous trichomes are the smallest type found on the cannabis plant and are usually too small to collect (about 20 microns in diameter), although they do secrete small amounts of cannabinoids and are found on nearly the entire plant surface.
- Andre, Christelle M., et al. “Cannabis sativa: The Plant of the Thousand and One Molecules.” Front Plant Sci, vol.7, no.19, 2016. Times Cited = 56 (PubMed) Journal Impact Factor = 4.298.
- Mahlberg P. G. & Eun Soo Kim. “Accumulation of Cannabinoids in the Secretory Cavity of Cannabis.” Industr. Hemp, vol.9, 2004, pp. 15–36. Times Cited = 27 (CrossRef)
Image Source: [Graphic 1]