Essential oil is the volatile aromatic fraction extracted from a herb or spice, typically by steam distillation, and serves as a key quality indicator because its composition and concentration directly determine flavour, aroma and commercial value.
In trade practice
Gas chromatography is the standard analytical method for verifying essential oil composition against reference profiles in ISO or European Pharmacopoeia monographs. QA teams check both total volatile oil content and the ratio of key marker compounds, such as linalool in coriander or thymol in thyme. Drying temperature and storage conditions are the most common causes of essential oil loss before testing. Buyers of flavouring-grade material typically request a certificate of analysis showing the full GC profile.
In a specification
A specification for herb or spice material states a minimum volatile oil content, expressed as millilitres per 100 grams on a dry basis, and may reference a named ISO monograph for the GC marker profile.