INTRODUCTION: Trichomes (fine outgrowths on plants) play several important functions for plants, primarily protecting the next generation of genetic material, the seeds, as dictated by natural selection and survival. Most trichomes do this in any or all of the follow ways:
(1) Production of odors (via terpenes and flavonoids) that attract bees and other insects that help pollinate the plant. Cannabis is air-pollinated (wind), however, so this is not part of the trichomes duty in cannabis.
(2) Production of odors that attract predators so herbivores stay away from the plant and don’t eat it.
(3) Production of psychoactive chemicals that get the herbivore ‘high’ (and/or chemicals that cause an upset stomach), so as to distract the herbivore from eating the plant (opium poppies, some mushrooms, jimsom weed, etc).
(4) Creation of physical barriers (such as cotton fibers, also trichomes), making it difficult for beetles and other pests to get to the seeds.
Once seeds begin to form, the plant no longer needs as much of these odorous and/or psychoactive compounds, and instead diverts resources to nurture seed formation instead. This is why, in an opium poppy pod, as the seeds begin to form the amount of opiates begin to decrease and become nearly nonexistent by the time the seeds are fully developed and ready to be released from the plant to start the next generation.
The total cannabinoid concentration in cannabis plants historically averaged between 1%-5% in a mature harvested plant. However, once it was discovered that cannabinoid concentrations could be increased by preventing pollination, total cannabinoid concentrations have increased dramatically in recent years, pushing these averages to 12%-16%. This was the beginning of sinsemilla (cannabis with high concentrations of psychoactive compounds) growing techniques in cannabis (which were already being applied to opiate cultivation and other medicinal plants).
YELLOW TRICHOMES: A very common belief is that yellow colored trichomes are a sign that the cannabis flower is old and that the trichomes are decomposing into unwanted material, such as CBN. This is a common misconception that is not necessarily true.
Firstly, not all cannabinoids are colorless. One of the most brightly yellow-colored cannabinoids is CBD, a VERY valuable cannabinoid. For example, when observing Harlequin strains under a microscope (regardless of how immature or old the flowers are), the yellow coloration of high CBD containing trichomes is immediately apparent, the flowers having a very different look than those of a classic high THC-A strain. Trichome head size is also usually smaller, and many CBD trichomes are sessile, meaning the trichomes are stalkless, the heads forming on the surface of the petals of the flower.
Secondly, all breakdown products (such as CBN) are not necessarily undesirable. CBN is currently documented for having the strongest medicinal sedative effect among all the cannabinoids. A patient having trouble sleeping will find CBN to be of high value in their treatment. The well known ‘couch-lock’ effect is most evident in cannabis containing high levels of CBN.
TRICHOME SIZE: At maturity, the stalks of trichomes will reach a maximum diameter of about 40 microns. The trichome heads will reach a diameter of about 120 microns (triple the stalk diameter), with a maximum upwards of 135 microns.
This is why, in the process of making kief, mesh sizes above 120 (125 micron pass through) are not commonly used. A finer mesh does not allow the largest trichome heads to pass through the mesh. Using a 170 mesh (88 micron pass through) retains most of the trichome heads, snapping off the trichome stalks, which do pass through finer mesh sizes. If the intention is to deliberately separate the heads from the stalks, a 200 mesh screen (74 micron) is used.
In practice, classic Afghani pressed hash contains a large amount of debris because large, 50-60 mesh screens are used.
TRICHOMES AND CANNABIS EXTRACTIONS: As to predicting cannabinoid concentrations in cannabis concentrates after extracting, the same general rules apply for both sinsemilla and non-sensimilla plants. Leaf matter in cannabis contains a very small amount of cannabinoids (around 0.5%) while the trichomes contain the majority of cannabinoids.
If you separate the trichomes from the plant matter in the flowers, kief will normally constitute about 1/3 of that total mass – ergo 30 grams of flowers will yield about 10 grams of trichomes. Those trichomes will be about 2.5 times as concentrated in total cannabinoids as the original flower (remember that a small amount was left behind in the plant matter itself).
Of those 10 grams of trichomes, approximately half the weight is made up of cannabinoids/terpenoids, while the other half is structural matter of the trichome itself. Thus, in 30 grams of flowers/buds, one can expect to extract a maximum of about 5 grams of terpenoids (cannabinoids included).
In a some cases, when trichomes are ‘overloaded,’ the ratio of total cannabinoids goes up, such as in a bud containing 30% THC-A, which would then yield a maximum (with ideal heating/decarboxylation) of 19% THC. Kiefing this flower would yield a maximum of about 47% THC. Further extraction/clean-up into a full melt concentration could concentrate this material to approximately 85% THC.