Terpenes are natural compounds found in many plants, responsible for a wide array of distinctive aromas. When a plant or plant-derived product emits an ammonia-like smell, it often raises questions. This article explores ammonia’s odor, typical terpene profiles, and other compounds that might be responsible for such a scent in plant materials.
Understanding Ammonia’s Distinct Odor
Ammonia is a colorless gas with a pungent, irritating smell. This sharp odor is widely recognized from cleaning products, fertilizers, and even urine.
Ammonia is highly volatile, readily evaporating into the air, and is also highly soluble in water. The human nose is sensitive to ammonia, capable of detecting its presence at concentrations as low as 5 parts per million (ppm). Even at low levels, exposure can cause irritation to the eyes, nose, and throat.
Common Terpene Aromas
Terpenes are diverse organic compounds found throughout the plant kingdom. These volatile organic compounds (VOCs) contribute significantly to plant scents.
For example, limonene provides a bright citrus aroma, often found in lemons and oranges. Pinene contributes a fresh, pine-like scent, while myrcene is known for its earthy, musky, and sometimes fruity notes. Other common terpenes include linalool, which offers floral and spicy undertones, and caryophyllene, recognized for its spicy, peppery, or woody aroma.
The vast majority of known terpenes do not produce an ammonia-like scent. Therefore, if a plant emits an ammonia smell, it is likely due to other compounds.
Compounds Mimicking Ammonia’s Scent
While terpenes typically do not smell like ammonia, other volatile organic compounds (VOCs) found in plants or generated during their decomposition can produce such a scent. The perception of an ammonia-like odor in plant material is often due to the presence of nitrogenous compounds, particularly amines and, in some cases, indoles. Amines are organic derivatives of ammonia that frequently form during the breakdown of proteins and amino acids in organic matter. Smaller amines can have an ammonia-like smell, while others, like methylamine, ethylamine, and trimethylamine, are associated with a fishy odor. Foul-smelling amines such as putrescine and cadaverine also arise from the degradation of amino acids in decaying biological material.
Amines can occur naturally in some plants as alkaloids, which are basic organic nitrogen compounds. Indoles, another group of nitrogenous compounds, can also contribute to distinct odors. Skatole, or 3-methylindole, is notable for its strong fecal odor at high concentrations, as it is a primary contributor to the smell of mammalian feces. At very low concentrations, skatole presents a pleasant, flowery aroma, found in flowers like jasmine and orange blossoms. Skatole is formed from the decomposition of the amino acid tryptophan. The formation of these ammonia-mimicking compounds in plant material is often linked to microbial activity, such as bacteria thriving in anaerobic conditions, or the natural degradation of plant tissue.
Decoding Ammonia Notes in Plant Aromas
When a plant or plant-derived product, such as cannabis, exhibits an ammonia-like smell, it typically signals an issue rather than a natural characteristic of its terpene profile. This scent can arise from the decomposition of plant material, where chlorophyll breaks down into ammonia. Improper curing or storage conditions are frequent culprits, as excess moisture and inadequate airflow can foster the growth of bacteria and molds, including species like Botrytis cinerea and Aspergillus. These microorganisms produce ammonia as a byproduct of their metabolic processes.
A high nitrogen content in the plant during its growth phase can also lead to an accumulation of compounds that result in an ammonia-like smell. While some plant cultivars may have subtle ammonia undertones, a strong ammonia scent usually indicates degradation or improper processing. Differentiating a true ammonia smell from other pungent plant notes involves recognizing its sharp, chemical quality. Visual inspection for mold or an overly damp texture, along with an acrid or chemical taste, can further confirm that the perceived ammonia odor is a sign of compromised quality.