Extraction Equipment

Subcritical Water Extraction (SWE)

Subcritical Water Extraction (SWE), also known as pressurised hot water extraction, uses liquid water heated above its normal boiling point but held below its critical point, with sufficient pressure applied to keep it in the liquid state. In this range the dielectric constant of water falls sharply, so the medium behaves progressively like a mid-polarity organic solvent and dissolves a wide spectrum of phenolics, flavonoids, polysaccharides and aroma compounds from botanicals. Because water is the only solvent, the extraction stage has no flammable organic solvent and no organic-solvent recovery step. Mechotech engineers turnkey SWE Extraction systems tailored to each feedstock and target compound.

Subcritical Water Extraction works by tuning temperature (typically in the sub-critical band up to around 374 degrees C) and pressure so that ordinary water gains organic-like solvating power without vaporising. Raising temperature lowers water polarity, viscosity and surface tension while improving mass transfer, which gives adjustable selectivity by changing the operating temperature rather than switching solvents. Because the medium is water, the extraction stage carries no organic-solvent recovery burden, and the thermal profile is controlled through the heating and cooling duty. Mechotech fabricates the extraction vessels, heat exchangers and high-pressure circuit in SS 304 and product-contact SS 316L to hygienic, GMP-oriented standards, with PLC/SCADA control of temperature, pressure and flow. Capacity is configured from pilot to commercial scale to suit each process requirement.

Process Flow

Technical Specifications

Technology	Subcritical Water Extraction (SWE) / Pressurised Hot Water Extraction
Working Principle	Pressurised liquid water heated below its critical point; falling dielectric constant makes water act as a tunable organic-like solvent
Operating Temperature	Configurable within the subcritical range up to approx. 374 degrees C
Operating Pressure	Configurable, set to keep water liquid at the chosen temperature
Solvent	Water (deionised / process water); no organic solvent in the extraction stage
Operating Modes	Static soak and dynamic flow-through (configurable)
Product-contact Material	SS 304 / SS 316L
Automation	PLC/SCADA (configurable) with recipe management and batch data logging
Capacity	Configured to process requirement - pilot to commercial
Utilities	Steam / thermic fluid or electric heating, cooling water, chilled water, power, compressed air
Compliance	GMP / cGMP hygienic design
Final Output	Aqueous extract; optional concentrate or dried powder via downstream evaporation and drying

Plant Capacities

Scale	Typical Use	Vessel Configuration	Operating Mode
Pilot / R&D	Process validation, parameter screening	Single extraction vessel	Static soak or dynamic flow-through
Small commercial	Standardised extract production	Sized extraction vessel with heat exchanger	Static soak or dynamic flow-through
Mid-to-large commercial	High-volume botanical or phytochemical production	Larger vessel, upgraded high-pressure pump and heat exchanger	Dynamic flow-through (typical for throughput)

Extraction vessel volume, heating/cooling duty, and pressure rating are engineered to the specified feedstock, throughput, and finished-extract specification; exact capacity is confirmed during process design.

Manufacturing Process

Feed preparation & loading

Milled or sized botanical material is loaded into the extraction vessel and the system is sealed. Correct particle size improves contact area and mass transfer during extraction.

Filling & pressurisation

Deionised or process water fills the vessel and a high-pressure pump raises system pressure. Pressure is set high enough to keep water liquid at the chosen operating temperature.

Heating to subcritical range

The water is heated through a heat exchanger or jacket into the subcritical band. As temperature rises the dielectric constant drops, turning water into a tunable, organic-like solvent.

Static or dynamic extraction

The hot pressurised water contacts the matrix in static soak or continuous flow-through mode. Target compounds dissolve into the water phase as mass transfer proceeds.

Cooling & pressure let-down

The loaded extract stream is cooled through a heat exchanger and the pressure is reduced in a controlled manner. Rapid, controlled cooling helps protect thermally sensitive actives.

Separation & collection

The aqueous extract is separated from spent solids and routed to collection. Fines are removed by filtration to yield a clean liquid extract.

Concentration & drying

The clarified extract can be concentrated by evaporation and converted to powder by spray or freeze drying downstream. This delivers a shelf-stable finished extract.

Cleaning & batch turnaround

Water flushing and CIP prepare the system for the next batch. Because only water is used, changeover and cleaning are simplified.

Major Plant Equipment

Extraction vessel (SS 316L product-contact)
High-pressure pump
Heat exchanger / heating jacket
Cooling / pressure let-down heat exchanger
Filtration / separation stage
Downstream evaporator and spray or freeze dryer (optional, separate Mechotech pages)
CIP connections
PLC/SCADA automation

Plant Output

Aqueous extractConcentrate or dried powder (optional, via downstream evaporation and drying)

Applications

Nutraceutical and dietary-supplement actives
Phytochemicals such as polyphenols, flavonoids and antioxidants
Essential oils, oleoresins and natural aroma compounds
Pharmaceutical botanical actives and standardised extracts
Food, beverage and natural flavour ingredients
Pectin, polysaccharides and functional carbohydrates
Cosmetic and personal-care botanical extracts
R&D, pilot studies and process scale-up

Key Features

Water as the Only Solvent
Water is the only solvent, which removes flammable organic solvents and organic-solvent recovery from the extraction stage; any residual-solvent testing for a product is set by its specification.
Tunable selectivity by temperature
Lowering the dielectric constant of water with temperature lets a single medium target different compound classes, so selectivity is adjusted without changing solvents.
Fast Mass Transfer
Reduced viscosity and surface tension of subcritical water improve penetration into the matrix, which can shorten extraction times; the yield for a feed is established in trials.
Controlled thermal profile
Integrated heat exchangers and rapid, regulated cooling help protect heat-sensitive natural products while still exploiting elevated-temperature kinetics.
Hygienic, GMP-oriented build
Product-contact parts in SS 316L with smooth finishes and CIP-friendly design support pharmaceutical, nutraceutical and food-grade production.
Full automation & data logging
PLC/SCADA control of temperature, pressure and flow with recipe management and batch records supports repeatable, traceable operation.

Frequently Asked Questions

What is Subcritical Water Extraction (SWE)?

Subcritical Water Extraction, also called pressurised hot water extraction, is an extraction method that uses liquid water heated above its normal boiling point but kept below its critical point. Enough pressure is applied to keep the water liquid, and in this state it can dissolve a broad range of botanical compounds using water alone as the solvent.

How does subcritical water extraction work?

As water is heated toward the subcritical region, its dielectric constant, viscosity and surface tension drop while its solvating power rises. The heated, pressurised water therefore behaves more like a mid-polarity organic solvent, penetrating the plant matrix and dissolving target compounds. Adjusting the temperature changes which compound classes are extracted, then the loaded stream is cooled, depressurised and collected.

What are the advantages of SWE compared with conventional solvent extraction?

SWE uses only water, so the extraction stage has no flammable organic solvent and no organic-solvent recovery step. Selectivity can be tuned simply by changing temperature, mass transfer is fast, and the process suits heat-sensitive natural products when cooling is well controlled.

What can a subcritical water extraction plant process?

It is well suited to phenolics, flavonoids and antioxidants, polysaccharides such as pectin, essential oils and aroma compounds, and standardised botanical actives for nutraceutical, pharmaceutical, food, beverage and cosmetic use. It is also valuable for R&D and pilot studies where a water-only, tunable method is preferred.

How does SWE differ from Mechotech's Aqueous Extraction?

Both use water as the sole solvent, but Aqueous-Based Extraction contacts feed with water at ambient or moderately elevated temperature, while SWE heats pressurised water well above its normal boiling point but keeps it below its critical point. That subcritical heating sharply lowers water's dielectric constant, giving it organic-solvent-like solvating power that plain aqueous extraction at lower temperature does not reach.

What capacity is available?

Mechotech configures capacity to the process requirement, from pilot and R&D systems through to commercial-scale plants. The extraction volume, heating and cooling duty, pressure rating and cycle time are all sized around the target feedstock, throughput and finished-product specification, and we recommend validating parameters on a pilot system before scaling.

What material of construction and compliance does Mechotech use?

Product-contact parts are built in SS 316L with SS 304 used for structural and non-contact areas, finished to smooth, CIP-friendly, hygienic standards. Systems are engineered following GMP and cGMP hygienic design principles so they suit pharmaceutical, nutraceutical and food-grade production, with documentation to support qualification.

Does Mechotech provide turnkey design, manufacture, installation and commissioning?

Yes. Mechotech designs, engineers and fabricates the complete subcritical water extraction system, including the pressure vessels, heat exchangers, high-pressure circuit and PLC/SCADA automation, and then installs and commissions it as a single integrated turnkey plant. We support the project through scale-up, training and process validation.

What information is needed to specify an SWE plant?

To configure the plant Mechotech needs the raw material and its particle size and moisture, the target compounds and their heat sensitivity, the temperature and pressure range wanted, whether static or flow-through operation is preferred, the throughput or vessel size, and the hygiene and documentation requirements. Temperature, pressure and cycle time are then set during process development on a pilot run.

Which related pages does Mechotech list?

Related extraction pages include Aqueous-Based Extraction, Pressurised Liquid Extraction, Ultrasound-Assisted Extraction and Microwave-Assisted Extraction, and the aqueous extract can be concentrated on the Falling Film Evaporator and dried on the Spray Dryer or Freeze Dryer / Lyophiliser. The hub is Extraction Equipment Plants.

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Subcritical Water Extraction (SWE)