These cannabinoid acids readily decarboxylate to form their corresponding cannabinoid on storage, in light, or on heating. Although, the principal psychologically active component of marihuana is the neutral cannabinoid, delta-9-tetrahydrocannabinol, its pharmacologically inactive acid forms, delta-9-tetrahydrocannabinolic acids (THCA) â??Aâ? and â??Bâ? contribute significantly to the psychoactivity of cannabis products when smoked. This occurs when the inactive THCA is decarboxylated to pharmacologically active THC when heated, as in smoking. The optimal temperature for conversion was reported to be 200 to 210 C at which 100% conversion to the neutral phenolic form of THC occurred. However, even at room temperature THCA slowly becomes converted to THC. For example, fifty percent of the THCA in marihuana stored for 1 year had been converted to neutral THC. Thus, fresh hemp ingredients, such as freshly pressed hemp oil or fresh hemp seeds could contain inactive THCA that would be readily converted into active neutral THC during baking and food processing or would be gradually converted over the shelf-life period.

One study was identified that measured the percentage of pharmacologically inactive THC-acids in 25 hemp oils (10 commercially available in Switzerland and 15 prepared from drug-type- and non drug-type- cannabis). It was reported that THCA in the hemp oil samples constituted <10% of the total THC content. This finding implies that the ratio of THCA:THC in hemp oil would be less than 1:10, versus a ratio of 10:1 for THCA:THC in fresh plant material. An explanation for this difference in ratios may be that the majority of THCA in plant material is converted to THC in the mature plant seeds, or during seed storage and processing (seed drying, cleaning and pressing).

Conversely, THC is rather unstable and is degraded by light, heat, acids and atmospheric oxygen; factors that contributed to the loss of potency of cannabis products on storage. Prolonged storage was reported to result in a decrease in the total THC content, as THC becomes oxidized to neutral CBN. The decrease in total THC was reported to be greater in the presence of light than dark; in light a 46% decrease in THC occurred after 47 weeks storage of marihuana vs a 23% decrease in THC in the dark.

Therefore, the cannabinoid content, including the active THC content, of hemp ingredients (i.e. hemp oil, hemp seed, hemp meal, hemp nut) and hemp products made with these may change with the processing and storage temperature, and age of the product. Since the reported rate of loss of THC (23- 46 %) over storage (approx. 1 year) was similar to the reported rate of THCA decarboxylation to THC (50%) during storage for 1 year, it is possible that these opposing chemical transformation processes would have a minimal effect on the overall active THC content in a finished product. Hence, the total THC content would be expected to remain relatively constant over the period of a year. One manufacturerâ??s observations concurred that over a 1 year period (the product shelf-life) measured total THC concentrations in industrial hemp oil were relatively constant. A study of the stability of cannabis and its preparations showed that a low THC content corresponded to a high CBN content and vice versa in drug-type cannabis resin.
http://www.hc-sc.gc.ca/cps-spc/alt_f...aluation_e.pdf

So after one year of storage, about 50% of the THCA has decarboxylated to THC. That's 25% conversion at 6 months, and 12% at 3 months. Conversely, conversion via heat is 100% on application.

So yes, if you wait long enough, you can munch on some bud directly. Practically speaking, heating is the assumed catalyst.