Cannabis Curing – Jar, Humidity, Duration and Storage

In curing, dried cannabis flowers mature for a few weeks in closed jars. Growers do it because the smoke is smoother and rounder afterwards and the aroma comes through better. In the jar the moisture still inside the flowers evens out: what is already too dry on the outside takes up water, what is still moist inside gives it off. In one trial, very dry flowers went from 6.1 to 11.5 % water this way, damper ones came down from 16.5 to 13.6 %. To keep mould from growing, the humidity in the jar has to be right, and a hygrometer, a small humidity meter, shows it.

Preparation

Only flowers that are dry enough go into the jar: thin stems snap when bent, and a test with a hygrometer in a closed jar shows no more than 65 %. Above that it is damp enough for frugal mould species to grow. Fill the jars loosely to about three quarters without pressing; the space at the top lets air get between the flowers. Keep them dark and cool. There are two ways to control the humidity from here: regular airing or a humidity pack.

Curing with airing

The classic way is to open the jars regularly. This airing is called burping. Why it is needed: water from the inside of the flowers moves outwards and collects in the air of the jar. Opening lets that damp air out and drier air in. The usual practice: during the first two weeks, open once a day for 10–15 minutes and turn the jar gently so the flowers move. From the third week every two to three days, after a month once a week. The goal is a reading that stays steady at 58–62 %. If it climbs above 65 %, leave the lid off longer. If it smells of ammonia or musty, the flowers are too wet and need a day spread out to dry.

The price of airing is aroma. In jars opened twice a week for a month, terpene content fell; terpenes are the plant’s aroma compounds. In practice: air regularly at first, while the flowers are still giving off moisture, and only rarely once the reading holds steady.

Curing with a humidity pack

The second way is a humidity pack, a pouch of salt solution that holds the air in the jar at a fixed level, usually 58 % or 62 %. Why it works: a saturated salt solution always sets the same humidity above it as long as undissolved salt remains in the pouch. If the air is damper, the pack takes up water; if it is drier, the pack releases some. The advantage over airing: the jar needs opening less often, and the value fluctuates less. The drawback: the pack has a limit. Once it has taken up so much water that all the salt has dissolved, it no longer regulates, and the air gets damper than printed, even though the pouch feels normal. Drying out, by contrast, shows as the pouch turning hard. One manufacturer recommends ten days at 50–55 % for its curing product and assumes fully dried flowers.

In practice: a hygrometer belongs in the jar even with a pack. If it shows more than 65 %, put in a fresh pack and give the flowers some air again.

Duration

Curing should last at least two weeks; many growers leave their flowers in the jar for four to eight weeks. What has been measured is that three weeks do the active compounds no harm: in a trial with industrial hemp the content of cannabinoids, active compounds such as THC and CBD, stayed the same over that time, and the microbe load did not rise. Longer mainly helps if the reading in the jar has not settled yet. The hygrometer decides, not the calendar.

What changes in the jar

The flowers turn paler because the green pigment, chlorophyll, is broken down; drying already does most of that. The smoke becomes smoother after curing, which is the consistent experience of growers. A small share of the cannabinoids turns from its precursor, the acid form, into the active form in the jar, mostly under 2 % in three weeks. Many also experience a stronger or rounder effect after curing. That hardly comes from the THC content of the smoke: the heat converts the acid form when smoking anyway, and in a trial THC acid delivered about as much THC in the smoke as ready-made THC. The aroma compounds keep evaporating in the jar, which is another reason it stays closed once the reading is stable.

Storage after curing

Store cured flowers whole, not ground, dark and cool in a tightly closed jar. Why: in a storage study ground flowers lost more aroma compounds than whole ones, and cannabinoids kept best at 4 °C. At 25 °C the THC acid dropped by about a third within a year. In a closed brown glass bottle the aroma lasted longer than in a plastic box or open. The freezer is no improvement; there even more terpenes were lost than at 4 °C. The loss of aroma cannot be stopped completely: even cool and dark, terpene content fell by more than half within four months. In practice: store in the fridge, and the best months are the first ones after curing.