“Full-melt” is one of the cannabis concentrate market’s most specific-sounding terms and one of its least formal. It refers to solventless hash that liquefies under heat and leaves little visible residue. The familiar five- or six-star designation is a trade convention, not a government grade.
Weedmaps’ current technical explainer says no universal star system exists, though a six-star scale is widely used by hash makers. Its scale places food-grade material at one or two stars, partial-melt material in the middle and full-melt material at five or six. A separate July 2026 explainer is more direct: six-star is not a regulated classification.
That boundary matters for buyers and manufacturers. A full-melt claim communicates expected physical performance. It does not certify cannabinoid concentration, residual pesticide status, microbial results, heavy metals or any other regulatory panel. Those questions belong to the certificate of analysis and the rules of the state where the batch is sold.
What is supposed to melt
The raw material is cannabis resin held in glandular trichomes. Peer-reviewed microscopy and proteomics research describes capitate-stalked trichomes as a head-and-stalk structure. Secretory cells at the base of the head produce cannabinoids and terpenoids, which accumulate in a cavity beneath the outer cuticle. The head is therefore both the target and a useful visual marker for mechanical separation.
Ice-water hash production uses cold water and agitation to detach trichome heads, then passes the mixture through fine screens that separate material largely by size. Dry sift uses screens without the water step. Neither process guarantees full-melt output. The separation can also collect stalks, leaf fragments and other plant material, while aggressive handling can rupture or deform the resin structures being sought.
Research on five cannabis genotypes found that glandular-head size, maturity and post-harvest condition vary. Head diameters in that study ranged across a broad span, and drying altered trichome morphology. That helps explain a rule hash makers learn quickly: a screen size is a collection fraction, not a quality grade. The most desirable fraction can change with cultivar, maturity and handling.
What the star system is measuring
The star system is built around melt behavior. Cleaner fractions dominated by resin heads tend to liquefy more completely; fractions carrying more nonresin plant material leave more residue. In practice, graders also look at the fraction under magnification, examine visible contamination and evaluate how a small sample behaves under controlled heat.
That makes the grade a process-control language. A manufacturer can use it to decide which fractions are released as loose full-melt hash, which are pressed into rosin and which are routed into other products. It can also support lot separation: combining a high-melt fraction with a lower one may increase total packaged weight while erasing the attribute that supports the higher grade.
But the system becomes misleading when a subjective star count is presented like an analytical result. Different graders can use different heat, surfaces, sample amounts and residue tolerances. Color can reflect cultivar and maturity as well as processing. A light fraction is not automatically clean, and a darker fraction is not automatically poor. Without a written house method, stars are difficult to compare across producers.
A credible internal standard can make the informal grade more repeatable. It should identify the sampled fraction and screen range, define storage and sample preparation, use the same heating surface and conditions, document the residue threshold, and record who graded the lot. Photomicrographs and post-melt images can preserve evidence for later review. None of that turns the scale into a regulated standard; it turns an undocumented opinion into a controlled manufacturer specification.