Over the years, cannabis packaging in legal or medical marijuana regions has become more sophisticated, with features designed to maintain freshness. The packaging on your marijuana products might have a harvest date on them, but flower doesn’t come with an expiration date. So even with producers upping their packaging games, you might find yourself wondering “does weed expire?”
About the two worst ways you can store your weed are on a tray, exposed to oxygen and light, and in a plastic baggie, just like your dealer’s baggies that are standard on the illicit market. You likely know that the environment around cannabis affects how the plant grows, but marijuana storage is also a key component of quality and freshness. Cannabis needs just the right balance of conditions to remain fresh, in-tact, and problem-free.
Cultivators go to great lengths to ensure your flower is packaged with the most optimal moisture content, usually in opaque packaging to keep the light away. You’re probably wondering why you still see transparent and clear containers lining your dispensary’s shelves. Well, old habits die hard and the practice of seeing and smelling the product on the shelf is still a key component for many people when it comes to deciding what to purchase. Some companies have even started replacing the oxygen in their packaged flowers with nitrogen to help maintain freshness.
Moisture and Mold in Marijuana
Moisture and water activity make a big difference when it comes to diminishing the shelf life of cannabis. Cultivators take extra care to ensure cannabis is packaged with the perfect moisture content.
While no two cultivators dry their flowers in the same way, all cultivators do dry their flowers and then undergo a process called “curing.”
Curing the cannabis allows the moisture that is trapped inside the bud to slowly dissipate from the flower without changing any of the cannabinoids or losing terpenes. Once the flower has the perfect moisture content, usually between 6 and 9 percent, it is placed into packaging where excess oxygen has been removed.
When you take it home, it’s important to try to maintain that balance.
If you lose too much moisture, it can change the integrity of your flower. Your flower will become brittle and it can lose essential terpenes that affect the potency and taste.
Too much moisture or water activity and the consequences are more serious. So serious, in fact, that the American Society for Testing and Materials (ASTM), which develops technical standards across many commercial industries, published the “Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower” in May 2018.
The ATSM defines water activity as “the (quantitative) capability of the cannabis flower in a sealed container to affect the humidity of the container’s headspace air.” Headspace is the air that surrounds the flower. Water activity measures vapor pressure against pure water. If water activity is at 0.55, it is 55 percent that of water.
During storage, cannabis should remain at a minimum of 0.55 water activity and a maximum of 0.65. Water activity increases with temperature, which is why light and temperature control go hand-in-hand as storage best practices.
The relationship between moisture content and water activity is complicated, but the international cannabis community is currently working to determine what the optimal moisture content is in packaged flower.
What we know now is that relative humidity above 65 percent can highly increase the likelihood that your weed will develop mold. According to the American Herbal Products Association, the drying process will dehydrate cannabis until it has a moisture content of less than 15 percent, and the curing process is where the remaining moisture is slowly removed to retain the volatile oils.
The Best Temperature to Store Your Cannabis
To extend the shelf life of marijuana, it should be kept in a cool, dark place at room temperature or slightly below. The ideal temperature to store your weed is below 70 degrees Fahrenheit, or 21 degrees Celsius.
High temperatures combined with high moisture activity and relative humidity can lead to mold and mildew. Mold thrives between 32 and 120 degrees Fahrenheit, or 0 to 49 degrees Celsius, and growth is most active between 70 and 90 degrees Fahrenheit, or 21 to 32 degrees Celsius.
High temperatures and arid environments dry out your flower and volatilize, or evaporate, sensitive terpenes, which will ultimately change the effects and taste of the flower. This is why some cultivators skip drying and make live resin extracts to preserve all the monoterpenes that are lost during the drying process.
Lower temperatures are not as problematic, but they can make it harder for THCA to decarboxylate into THC. Lower temperatures will reduce the potency of the flowers when they are smoked, or could make the trichomes brittle on the plant, causing them to break off when they are removed from the cold environment.
Light and Oxygen Change Cannabis Composition
Exposure to light is the biggest culprit when it comes to aging weed. This has been known as far back as 1976, when a study published in the journal Pharmacy and Pharmacology explored what happens to the stability of cannabis under different conditions. It concluded that light is the single largest contributor to loss and deterioration of cannabinoids and suggested that “carefully prepared herbal or resin cannabis or extracts are reasonably stable for 1 to 2 years if stored in the dark at room temperature.”
Ultraviolet (UV) light will always degrade your cannabis, and while the clear glass jars you see in the marketplace look nice, they won’t protect your purchase the way an opaque container would. If you really like to look at your marijuana, a brown container will filter out visible ultraviolet light — that’s why brewers use them to bottle beer. Meanwhile, green containers will block out roughly 30 percent of UV rays.
As time goes by, prolonged exposure to light, heat, and oxygen will gradually convert THCA into THC. At the same time this is occurring, existing THC is being converted into CBN, without the intense psychoactive properties that THC delivers. And it’s not just THC that’s affected. CBDA can transform into CBD with enough exposure and THCV will degrade into CBV. During this time, your weed could potentially become less potent.
In addition to playing a role in the conversion of cannabinoids, oxygen can also oxidize essential terpenes and change the overall aroma of the flower into a grassy, haylike smell.
To reduce exposure to oxygen, make sure there aren’t many air pockets in your container. Don’t use very large containers to store small quantities of weed. If you store your weed in sealed bags, remove as much air as possible before sealing. Vacuum sealing is a reliable way to store your marijuana long term, while a handheld vacuum pump is helpful for short-term storage.
It is inevitable to introduce fresh oxygen into a sealed package once it is open, but you can limit the amount of time that the jar is opened and the amount of times it is opened.
Extending the Shelf Life of Weed
To reduce exposure to the elements, when it’s time to open your container, pull out your flower and immediately close your package. Don’t just let it sit open, and avoid windy or highly ventilated areas.
To maintain the right level of moisture, use a salt-based control sachet to maintain the ideal relative humidity. According to the ASTM standards (D8197-18), “a salt-based control sachet designed to maintain a relative humidity of 0.55 to 0.65 in a sealed container can be used to maintain optimum storage conditions.”
In the past, to remedy dry weed, people would add an orange peel to their bags to keep the moisture content, but this highly increases the likelihood that mold will be introduced. In addition, the water activity of orange peels is unknown and the aroma of the peel could alter the flavor and aroma of your weed.
Nowadays, you can use the same humidity control packs to reintroduce moisture if it is too dehydrated. This will not reintroduce terpenes that were lost, but it will ensure that you don’t have a harsh smoking experience.
Like almost everything else, weed doesn’t last forever. Over time, changes to the molecular structure occur with exposure to heat, light, and moisture.
When cannabinoids and terpenes experience very high or very low temperatures, dry up, are exposed to too much moisture, or are left in the presence of light, chemical changes that will degrade the potency of the flower and could alter the taste and mouthfeel may occur.
As terpenes are exposed to environmental changes, they can oxidize or evaporate, creating a change in aroma and effects. And even though all weed degrades over time, the process can be slowed down if you control the temperature, moisture, and the amount of oxygen your flower is exposed to. To keep your weed in tip-top shape as long as possible, keep an eye on the harvest date on the packaging and take careful steps to avoid exposure to light, moisture, oxygen, and extreme temperatures.