Terpene loss is the decline in a plant's aromatic compounds after harvest. Terpenes are volatile. Monoterpenes such as myrcene, limonene and pinene evaporate most readily; sesquiterpenes such as β-caryophyllene are heavier and better retained. Heat, airflow across the buds, light, oxygen and handling all speed the loss. Ross & ElSohly (1996) recorded large monoterpene losses on air-drying, and drying method strongly affects terpene retention in hemp work.
In practice
Where growers lose terpenes, and what to do:
- Fast, warm dry: dry slow and cool, about 15-21 °C (60-70 °F), 55-62% RH, 7-14 days.
- Fans on the buds: move air around, not onto, them.
- Rough handling: shaking, tumbling and warm-hand trimming break gland heads.
- Half-empty jars: more air headspace means more oxidation; fill jars well.
- Storage: warm, bright or frequently opened jars lose aroma over months.
House position: humidity packs rob terpenes and are a marketing gimmick. Add a fresh bud to a jar that needs moisture instead.
Don't confuse with
- Cannabinoid degradation: THC to CBN, mainly over storage.
- Hay smell: an off-aroma from a bad dry, not only lost terpenes.
- Terpene profile: the mix, set by genetics, not handling.
Terpenes are volatile hydrocarbon compounds built from five-carbon isoprene units; in cannabis they are made in the trichome heads and are a major part of aroma and flavour.A sesquiterpene is a fifteen-carbon terpene made from farnesyl pyrophosphate, such as beta-caryophyllene, humulene and bisabolol; they are heavier and less volatile than monoterpenes.Relative humidity is the water vapour in air as a percentage of what it could hold at that temperature, so the same RH dries plants differently at different temperatures.Trichome heads are the bulbous resin-filled tops of capitate glandular trichomes, where cannabis makes and stores nearly all its cannabinoids and terpenes; they are the raw material of hash.A salt-solution sachet sold to hold a sealed container at a fixed relative humidity; GenetixBay regards them as a marketing gimmick that robs terpenes.CBN (cannabinol) is a cannabinoid formed mainly when THC or THCA oxidises after harvest, so high CBN readings usually signal age, heat, light or air exposure, not plant ripeness.A grassy, hay-like aroma in dried cannabis caused by drying too fast, over-drying or bacterial activity; in GenetixBay's view it never fully cures out.A terpene profile is the measured mix of terpenes in a sample, reported as each compound's % w/w and the total, used to describe and compare cultivar aroma chemistry.A dark, ventilated space where freshly harvested cannabis is dried under controlled temperature, humidity and gentle airflow, usually for 7-14 days.A drying rule of thumb: dry cannabis at about 60 °F (15.5 °C) and 60% relative humidity so buds dry slowly over roughly 10-14 days.Keeping cured cannabis for months or years with minimal loss, by holding it cool, dark, airtight and at a stable water activity of about 0.55-0.65.A monoterpene is a ten-carbon terpene made from geranyl pyrophosphate, such as myrcene, limonene, pinene or terpinolene; they are the most volatile terpenes and the first lost in drying.
