We prefer to age all glands indoors. It may take several years for good breakdown to occur. However, they are very consistent in age, odor and color. All of our glands are a gold like tan to beige color and the resulting odor is that musky natural gland odor of that animal species . Key is starting with clean cuts without feces and minimal hair as is reasonable.
Starting with poorly handled glands with feces, excess tissue, blood etc. will yield a sour sewer like odor when aged with all that bacteria. Some like that type of odor however I do not. Animal reactions are different with each process.
Grind everything as fine as is possible before aging as this will speed up the tissue breakdown. It also will make working the material after aging much easier. Stirring occasionally will ensure consistent breakdown throughout the material. Once the glands have reached the age and consistency you want, you can preserve them well , and they will last forever until such time they are needed for use.
Outdoor aging is all over the place with temperatures and can alter the final odor significantly, as well as risking exposure to flies and animal concerns getting into your products. Try different batches aged indoors and outdoors and see what smells most natural and has that subtle musky odor as glands should possess.
In formulation work consistency is desired and needed to keep product quality high and standardized as much as is possible.