Classical methods of extraction are mostly based on the extracting power of different extraction solvents and the application of heat and/or mixing.
Usually following extraction techniques are considered as classical extraction techniques:
- Maceration,
- Extraction by organic solvents with application of heat and/or mixing,
- Soxhlet extraction,
- Hydrodistillation.
Classical methods of extraction are usually used for hand-made production or in pharmaceutical industry for preparations of different tinctures and liquid extracts (as axample: Salvia officinalis extract, Cammomile extract, Thymus vulgaris extracts etc.). Here, as classical extraction technology maceration is mostly applied, while as extraction solvents water, aqueous ethanol, ammonia solution, and glycerol are mostly used. Maceration represents the most simple solid-liquid extraction technique without agitation or additional heating.
Classical extraction by orgnic solvents is used for isolation of certian compound or mixture of compounds, or for preparation of semi-products that further need to be purified and processed. In this classical extraction technology usually additional heating and agitation are applied. As extraction solvent following solvent are used: water and water ethnol solutions, methanol, hexane, methylene chloride, chloroform etc.
The Soxhlet extraction is usually used on laboratory level for extraction of lipid comopunds. RSC defined Soxhlet extraction as the process of transferring the partially soluble components of a solid to the liquid phase using a Soxhlet extractor. In the Soxhlet extractor solid is placed in a filter paper thimble which is then placed into the main chamber of the Soxhlet extractor. The solvent (heated to reflux) travels and circulates through the main chamber of extractor transferring the partially soluble components into the solvent.
Hydrodistillation is used for essential oil isolation and production.
Main drawbacks of these methods are:
- low yields of extraction,
- increased degradation of sensitive constituents,
- long extraction time,
- high energy consumption,
- trace of toxic organic solvents in obtained extracts/final products,
- high cost of following purification processes,
- negative impact on environment.