Several machine types are marketed for treating food residues in professional kitchens. On a datasheet they look alike: stainless-steel units loaded from the top. In operation they do fundamentally different things, and the difference determines two things a brochure rarely states clearly: what leaves the machine, and what you are still left with at the end.
Three technologies, not two
The word "dehydrator" is used for two different machines. Add the aerobic digester and there are three approaches to compare.
1. Thermal dehydrator
Heating elements raise the chamber temperature and drive off water as vapour over a cycle of several hours. What remains is a dry, granular material, typically 10 to 20 % of the input mass.
The vapour is not pure water. Heating food residues releases volatile organic compounds (fatty acids, ammonia, sulphur compounds) and can carry fine droplets of fat. That is why these machines are fitted with a condenser, which turns the vapour back into a liquid discharged to the drain, and usually an activated-carbon or catalytic odour filter that needs periodic replacement. A thermal dehydrator also has a liquid discharge; it is simply less visible.
Evaporating water costs energy by physics, roughly 2.3 MJ per kilogram, so electricity is the dominant operating cost. Many models also pre-shred the input with cutting blades.
The dry output is still classified as food waste in most European jurisdictions. It has been reduced, not eliminated: it must be stored and collected or, where regulations allow, used as a soil amendment. Whether that route is available depends on the country and on whether animal-derived residues were processed.
2. Mechanical dehydrator (dewatering unit)
This machine does not heat. It grinds the residues and presses the liquid out, with a screw press or a centrifuge, sending it directly to the drain. A wet solid cake remains, typically 30 to 50 % of the input mass.
It is fast and uses little energy. Two consequences follow. The liquid entering the drain is unfiltered organic wastewater with a high organic load and fat content, which water operators examine more critically than a biologically treated effluent. And the cake, being wet, still requires regular collection and is prone to odour in storage.
3. Aerobic digester
Microorganisms, supported by enzymes and continuous aeration, decompose the material biologically into water, carbon dioxide and dissolved compounds. The liquid is filtered and discharged through the existing drain. No solid residue remains.
The process runs continuously at ambient temperature, with no heating phase and no batch cycle, so power draw is limited to mixing and aeration, and material can be added as it arises during service.
Two conditions apply. The machine needs a drain connection, and the discharge conditions should be confirmed with the local water operator, as with any equipment discharging to the sewer. And digesters have input limits: large bones, shells and very high fat loads are processed slowly or not at all; each manufacturer specifies what the microbial culture handles.
The fork that fell in
Every kitchen eventually drops cutlery, a bottle cap or a piece of crockery into the waste stream. In a machine with cutting blades, a screw press or a grinder, a steel fork is a mechanical failure: bent blades, a jammed press, an expensive repair and, more costly still, days without a working unit while the kitchen keeps producing residues.
The Griffon digester has no cutting or grinding elements. The material is mixed by a parallel-geared mechanism and aerated; a fork simply sits in the chamber until it is retrieved and, recovered promptly, goes back through the dishwasher. The machine is unaffected. When comparing units, ask specifically what happens when metal enters the chamber and what a repair costs.
The same question applies to longevity in general. Fat, salt, continuous loading and the occasional foreign object are the real operating conditions of a restaurant kitchen. A useful test of any supplier's claims is to ask for reference installations older than two years, and to call them. Griffon units have been in continuous operation since 2022 in hotels, hospitals and canteens in seven countries.
Measured, not claimed
Independent data is scarce. A 2022 study by the University of Zagreb's Faculty of Geotechnical Engineering compared the carbon footprint of food-waste management methods used in catering and measured, per tonne of residues treated, approximately 346 kg CO2e for thermal dehydration and 21.4 kg CO2e for on-site aerobic digestion with the Griffon unit. The difference is almost entirely heating energy and the transport of residue that still has to be collected.
How to decide
The choice follows from the site, not from the brochure. Is there a drain where the machine will stand? Without one, a thermal dehydrator is the realistic option, although it too produces a condensate that has to go somewhere. What do you want to eliminate: volume, or the collection contract? Dehydrators and dewaterers reduce volume and collection frequency; a digester removes the collection route, because nothing solid remains. And what is in your residue stream? Kitchens with large quantities of bones or shellfish should check a digester's input specification. Every kitchen should check what a dropped fork costs.
For most hotels, restaurants, canteens and hospital kitchens the answers are straightforward. Where a drain is available and the aim is to stop paying for collection, the energy figures, the residue question and the measured emissions point in the same direction. Griffon digesters are designed and manufactured in the European Union in five sizes from 70 to 1000 kg per day; the full technology comparison and the sizing calculator are available on this site.