Simply put, decarboxylation is the removal of a chemical group (a carboxyl group) from a cannabinoid and thereby increasing the amount of the active form of that cannabinoid. The fact of the matter is that the raw hemp plant itself has relatively low levels of CBD—to “activate” the CBD, decarboxylation is a necessary first step, whether you buy it from a company (and THEY do the decarboxylation) or you make your own from raw high-CBD hemp plants.
A carboxyl group is an organic group where the carbon is double bonded to an oxygen, a hydroxyl (-OH) group and the rest of a molecule. In the process of decarboxylation, usually done by either heating raw high-CBD content hemp or raw cannabis or by simply aging the harvested plant, the process results in the conversion of the acidic and less active form of CBD (Cannabidiolic acid or CBDA) into the more active form, cannabidiol or CBD. CO2 gas is produced as a by-product.
In general, and up to a point, the longer you decarboxylate (decarb) high-CBD hemp or high-CBD cannabis, the more activated CBD will result. The process is not 100% efficient, so you will never completely convert all the CBDA to CBD, so most recommendations are to heat the plant product at 250o F for no more than 60 minutes.
The acidic forms of most cannabinoids, including CBD, are found at higher levels in the raw plant than the more active “neutral” forms.  Decarboxylation increases the amount of “activated” CBD and other cannabinoids. One of the most common reasons someone may decarboxylate is for preparing edibles.
Vaping uses heat—so if you use vaping as a delivery method, decarboxylating is likely an unnecessary extra step.
Buying CBD isolate means that the CBD has already been decarboxylated—the same is true for both full- and broad-spectrum CBD. The company has already decarboxylated or decarbed the raw plant and has already converted most of the CBDA to CBD.
If on the other hand, you make edibles from raw, unprocessed high-CBD hemp, decarboxylating is a very important first step in the process because it allows you to extract the most CBD from the raw flowers.
If you want to make your own topicals, oils or tinctures, the same is true—to get the most CBD from the raw plant/flowers, you will need to decarboxylate—and it all can be done in your own kitchen.
There are lots of variations and “recipes” for decarboxylating hemp flowers—they are essentially the same though. You need not worry about the “best” way either—because you will never convert 100% of the CBDA into CBD in your kitchen, but that is just fine because CBDA has its own benefits—and is more bioavailable!  CBDA is, for example, being investigated as an anti-inflammatory agentand as an anti-nausea agent.
The “neutral” CBD (the non-acidic form) has been shown to benefit anxiety, depression, insomnia (sleep issues) and painful conditions. It is used (often in synthetic form) in mainstream medicine to treat nausea and seizure disorders. 
One tip that can be very helpful is to get an oven thermometer to ensure your oven provides heat at the correct temperature—temperatures in ovens can vary over a wide range and the readings you get from an oven thermometer may be more accurate than the settings indicate.
Another tip is to spread your raw plant material (flowers, buds etc) evenly over the bakeware.
Finally, resist the urge to keep opening up the oven and checking—that will throw the temperature off considerably and you do want to keep the temperature consistent for the entire time.
You can grind the flowers or just separate the flowers by hand—if you grind the flowers, you won’t have to heat for quite as long. On the other hand, grinding can cause some loss of material—ultimately, it comes down to your preferences and the equipment you have available. If you choose to grind the flowers, you can use a mortar and pestle or a food grinder—again, your preference. However, grinding will also end up increasing the amount of chlorophyll in your final product—and lots of people have little appreciation for the taste of chlorophyll! But…chlorophyll, the green pigment responsible for photosynthesis and the conversion of sunlight into energy, also has benefits by absorbing various toxins and acting as an antioxidant.
You may also want to decarboxylate your flowers in a covered oven-safe container—because, be warned, the odor of baking flowers may “infuse” your entire home—and if you have young children or sensitive others around, it may not be very appreciated.
Finally—to do the actual decarboxylation, the most common approach is to bake the materials (ground or separated by hand) at 240o F for 80- 90 minutes. The decarboxylated material can be stored in a mason jar or other tightly lidded container in a cool, dark spot. You can also store in your freezer though it is not essential.
You can also combine decarboxylation and infusions by making CBD-infused oils and butters by cooking the oils and butter for a longer period of time—again, you should be aware that combining these can make the butters and oils have a stronger chlorophyll taste (and look a bit greener too!)
This easy recipe will make infused cannabutter or infused canna oil.
In a medium saucepan, melt the butter slowly over low heat or heat the oil (slowly, low heat). Slowly add the water and your decarboxylated hemp. Stir every 10-15 minutes and simmer for 4 hours. Use a thermometer to make sure the temperature stays below 180oF.
After cooking for 4 hours, cool and strain the mixture through a cheesecloth. Store in the refrigerator or freezer in a tightly sealed container. You can use the cannabutter or canna oil in any recipe calling for butter or oil.
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