Why do my curing jars smell like ammonia?

Short answer

An ammonia or musty smell in a curing jar means the buds went in too wet and microbes have started working on them. It is the step before visible mould. Tip the buds out now, check the cores, and dry them until a sealed sample reads a stable 58–65% RH. Burping more often won't fix it. Grower practice.

Why

Wet buds feed microbes. Above water activity 0.65, dried flower is outside the ASTM range that guards against mould, and above 0.68 it needs further drying ^[1]^[2]. A sealed jar holds that moisture against the buds.

The smell is a warning. Growers report ammonia, sour or musty notes in over-wet jars before any fuzz appears, which fits microbes breaking down plant tissue. There is no cannabis study of the chemistry, so read the smell as a moisture alarm.

The safety risk is mould. Mouldy flower can carry spores and mycotoxin-producing fungi, which is why regulated markets test for yeast and mould ^[3].

The numbers

Sign	Meaning	Action
Faint ammonia or sour smell	Too wet	Tip the buds out and dry them
Equilibrated jar above 65–68% RH	Too wet ^[2]	Dry the buds further
75%+ RH overnight	Jarred far too wet	Dry them now
Fuzz, grey dust, brown core	Mould	Throw it away
Stable 58–65% RH, clean smell	Ready	Re-jar and cure

What to do

Empty the jar onto a clean screen or tray. Break open the biggest buds.
Throw out any bud with fuzz, dust, a brown core or a strong musty smell.
Dry the rest in the dark at 15–21 °C (60–70 °F) and 55–62% RH, usually 12–48 hours.
When the stems snap, re-jar loosely to about ¾ full in a clean jar.
Leave it sealed 12–24 hours, then read the hygrometer. Re-dry if it is above 65%.
Burp once or twice a day for the first week and sniff every time.

Common mistakes

Burping more often instead of drying the buds.
Jarring by feel without a sealed hygrometer test.
Packing jars tight.
Over-correcting into crispy, hay-smelling buds.

Full article: Curing and burping
Answers: mould in jars · how full to fill jars · how soon can I smoke?
Article: drying
Terms: burping · water activity

Follow-up questions

Is ammonia-smelling weed safe to smoke?

Ammonia-smelling cannabis is a warning sign, not proof of mould, but treat it with suspicion. Break open the buds: any fuzz, grey dust, brown core or lasting musty smell means discard them. Buds that dry out clean and lose the smell are usually usable, though some aroma may be lost. When in doubt, throw it out, especially for anyone with a weak immune system.

Will the ammonia smell go away?

A mild ammonia smell usually fades once over-wet cannabis buds are dried back to water activity 0.55–0.65 and cured properly, according to grower practice. A strong, lasting sour or musty smell, or a hay smell after an over-correction, rarely clears fully. Act on the first whiff: tip the jar out and dry the buds, rather than just burping more often.

How do I stop jars smelling of ammonia next time?

Stop curing jars smelling of ammonia by jarring only properly dried buds: small stems snap and a sample sealed for 12–24 hours reads a stable 58–65% RH. Fill jars loosely to about three-quarters, burp once or twice a day in the first week and sniff each time. A jar that jumps to 75% RH or more overnight needs emptying and drying.

Sources

ASTM D8197. Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower. store.astm.org/d8197-22.html

ASTM International, Standardization News. Two cannabis standards you should know about (salt-based humidity control sachets for aw below 0.68). sn.astm.org/node/2445/printable/print

Punja ZK, Collyer D, Scott C, et al., 2019. Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in Plant Science 10:1120. frontiersin.org/articles/10.3389/fpls.2019.01120/full