Curing in Glass Jars
Controlled aging of dried flower in sealed glass at 58–65% RH to improve flavor and stability.
Growing, buying or possessing cannabis and seeds is legal only in some places. Check the law where you live before acting on this information.
Curing is real and worth doing, but it's not magic. It won't increase THC (that requires heat, not time). What it does: removes harsh taste, stabilizes cannabinoids against degradation, and prevents mold if you hit the humidity sweet spot. The main variable is discipline—especially during the first week. Get burping right, and most flower tastes noticeably better by week 2-4. Skip the burping, and you're inviting mold.
What It Is
Curing is the controlled aging of already-dried cannabis flower in a sealed glass container at a stable relative humidity (RH), typically 58–65%, with periodic air exchange ('burping'). Over days to weeks, residual compounds break down, harsh volatiles dissipate, and cannabinoids stabilize in a low-oxygen, temperature-stable environment.
Curing is distinct from drying. Drying brings flower from ~75% moisture to ~10–12% moisture over 7–14 days. Curing takes that already-dry flower and lets it finish equilibrating slowly. Drying is necessary; curing is optional but strongly rewarded.
Why Growers Cure
Growers cure for three reasons:
1. Flavor and smoothness. Uncured flower tastes 'green,' hay-like, or harsh. Cured flower is smoother and more aromatic. This is consistent across decades of documented grower experience and is easy to verify yourself with a side-by-side comparison Anecdote.
2. Potency preservation. THCA is relatively stable in cool, dark, sealed glass. Heat, light, and oxygen degrade cannabinoids over weeks and months; a proper cure environment minimizes all three Strong evidence [1][2]. Uncured flower loses cannabinoid potency faster in storage.
3. Microbial safety. Flower stored above 65% RH supports mold growth, particularly Aspergillus and Penicillium. Flower stored below 55% RH is brittle and loses terpenes rapidly. The 58–62% RH window is the practical sweet spot for both safety and quality Strong evidence [3].
What curing does not do: it does not increase cannabinoid content. Decarboxylation (THCA → THC) requires heat, not time at room temperature in a jar. Claims that curing 'raises THC' are folklore No data.
When to Start
Start curing when the flower has finished its primary dry. Practical indicators:
- Small stems snap with a clean sound; larger main stems still bend slightly (not brittle).
- Outer flower feels dry to the touch; interior is no longer cool or damp.
- A digital hygrometer placed in a sealed jar with a sample reads 60–65% RH after 1–2 hours.
If your flower reads 70%+ RH when jarred, you are incubating mold, not curing. Pull it back out and dry further. If it reads under 55%, you've over-dried; rehydration with a two-way humidity pack is possible, but the cure will be slower and less effective.
How to Do It: Step by Step
1. Trim and prepare. Remove all obviously moldy, diseased, or damaged buds and discard them. Do not jar them next to clean flower.
2. Choose jars. Wide-mouth glass canning jars (Mason or Ball, quart or half-gallon size) are the standard. Glass is inert, seals reliably, and is easy to inspect. Avoid plastic for curing—it can off-gas over time and is harder to seal consistently.
3. Fill jars to about 75% capacity. Leave headroom so buds are not crushed and air can exchange during burping. Pack loosely; avoid compression.
4. Add a digital hygrometer. Small hygrometers designed for humidors or cannabis jars cost $5–15 and are essential. Eyeballing humidity does not work and leads to mold or over-drying.
5. First week—burp 2–4 times daily. Open the jar fully for 5–15 minutes to vent accumulated moisture and ammonia (from chlorophyll breakdown) and bring in fresh air. If RH stays above 65% after burping, the flower needs more dry time: leave the jar open longer or remove the flower and air-dry for a few hours.
6. Week 2—burp once daily. RH should stabilize around 60–62%.
7. Weeks 3–4—burp every few days. The aroma should shift from 'grassy' to the strain's true terpene profile.
8. Weeks 4–8+—long cure. Burp weekly, or add a two-way humidity pack and leave sealed. Store jars in a cool (15–20°C / 60–68°F), dark place.
Most growers consider flower 'cured' at 2–4 weeks and 'well-cured' at 6–8 weeks. There are diminishing returns past about 2 months for most cultivars.
Common Mistakes
- Jarring too wet. The most common failure. If you smell ammonia when you open the jar, your flower is too moist and anaerobic breakdown is occurring. Unjar immediately, spread out, and dry further. Do not leave it sealed.
- Not burping consistently. Sealed jars at 62% RH with damp flower will mold within days. Burp on schedule, especially in week one.
- Storing in direct sunlight or heat. UV radiation and high temperature degrade THC and terpenes. A dark closet or cupboard is appropriate; a windowsill or warm room is not Strong evidence [1].
- Mixing different strains in one jar. Terpene profiles will cross-contaminate. Use one jar per strain per harvest.
- Vacuum-sealing during the active cure. Vacuum sealing is fine for long-term storage after the cure is complete, but during active curing flower needs periodic air exchange to burp off moisture and ammonia.
- Using a humidity pack to rescue flower jarred too wet. Two-way humidity packs stabilize moisture in already-correct flower. They cannot dry out flower that was jarred at 70%+ RH fast enough to prevent mold.
Related Techniques
- Water curing: Soaking flower in water for several days to leach soluble compounds. Produces nearly odorless, very smooth smoke at the cost of significant terpene loss. Uncommon.
- Freeze drying: Removes moisture under vacuum at low temperature. Faster than air drying and preserves terpenes well, but still benefits from a short jar cure afterward.
- Curing in CVaults: Stainless-steel containers paired with humidity packs. Functionally equivalent to glass jars for the cure itself; preferred by some commercial operations for stacking and durability.
- Long-term storage: After a full cure is complete, flower can be vacuum-sealed or kept in sealed jars with humidity packs in a cool dark place for 1–2 years with modest cannabinoid loss Strong evidence [1][2].
Sources
- Peer-reviewed Trofin, I. G., Dabija, G., Vaireanu, D. I., & Filipescu, L. (2012). The influence of long-term storage conditions on the stability of cannabinoids derived from cannabis resin. Revista de Chimie, 63(4), 422–427.
- Peer-reviewed Lindholst, C. (2010). Long-term stability of cannabis resin and cannabis extracts. Australian Journal of Forensic Sciences, 42(3), 181–190.
- Peer-reviewed McPartland, J. M., & McKernan, K. J. (2017). Contaminants of concern in cannabis: microbes, heavy metals and pesticides. In Cannabis sativa L. – Botany and Biotechnology (pp. 457–474). Springer.
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