Although, qualitatively, the specific aromatic profiles remain recognisable and within acceptable limits, a quantitative variation is often observed between different crops and batches of the same plant material and also between the several parts of the plant which may be used. Because of this variation it is difficult to be precise in describing the aromatic effects of plant materials and assessment is generally a matter of judgement of acceptability for a particular use. Thymol-like Ocimun spp. Examples are fruits, fruit juices, spices, herbs, cheese and vinegar. Examples are essential oils, oleoresins, extracts and distillates.
Examples are citral, geraniol, and menthol.
The ingredients with major industrial use are in the form of essential oils and extracts. Most essential oils are used directly as starting materials in the production of flavour and fragrance compositions. However, some essential oils are fractionated or concentrated by distillation, partitioning, or adsorption. Substances that are important for the desired characteristic odour and taste are thus concentrated, and other components, which possess either an unpleasant or very faint odour or are unsuitable for the application in question, are removed. Individual compounds can be isolated from essential oils containing one or only a few major components by distillation or crystallisation.