Tuesday, September 9, 2014

Are Automatic Grease Removal Devices the Answer?

I regularly get asked to talk about Automatic Grease Removal Devices (AGRD), you know, the pro's and con's.

I fully realize that blogging about this topic is risky.

By risky, of course, I mean like when a woman says, "does this dress make me look fat?" and you are stupid enough to say, "it's not the dress!"

It may be true, but that won't save your life.

It doesn't matter what the AGRD looks like or how it works, the underlying concept is flawed.

Okay, before you hit the send button on that you-should-die-a-horrible-death-because-you-suck-you-ignorant-jerk email, let me explain.

The devices are not flawed - its the concept behind them that is flawed.

I don't have reason to doubt manufacturer's claims of performance, because many of them have been tested to ASME A112.14.3 and A112.14.4.

So what is the flawed concept behind them?

While specific design elements vary by manufacturer there are several general design elements that most AGRDs share.
  • Heating element - most manufacturer's require a heating element that keeps the contents of the AGRD liquified, which makes transporting the FOG easier.
  • Motorized skimming device - a means of removing the accumulating FOG from the AGRD.
  • Attached exterior collection container - where the accumulated FOG is deposited by the skimming device.
Nearly all manufacturer's instruct the restaurant to maintain their interceptor on a daily basis.  As the collection container fills with FOG it must be emptied.

The nature of the collection container being attached to the side of the unit requires it to be readily accessible for removal and replacement.  Normally this restricts the installation of these devices to above the floor where they are limited to the number of fixtures that can be effectively routed to them.  That is why they are usually sold as a point-source interceptor.

Okay so here's the conceptual flaw - restaurants do not discharge 100% of there FOG through just one fixture in the kitchen, i.e. three-compartment sink. 

Yes, I have heard the argument that 90% of the grease in a commercial kitchen is handled through the multi-compartment sink.

No, I have not seen any credible independent studies that conclusively prove this hypothesis. In fact the most experienced FOG inspectors in the industry dispute this claim with passion.

Also, I have been in actual kitchens in the field, you know, where real people are busy cooking and cleaning.  I've seen the grease that runs down the front of the fryers, and the greasy spills on the kitchen floors.  I've noticed the grease build-up on the walls.  I've seen kitchen staff scraping food scraps from dishware into the food grinder sink, that isn't routed to a grease interceptor.  I've seen people dump residual soup down the hand sink because it was the closest fixture.

There is a very basic scientific principle which explains this phenomena.

Harvard Law states, "under the most rigorously controlled conditions of pressure, temperature, volume, humidity, and other variables, an organism will do as it damn well pleases."

That pretty much describes a working commercial kitchen.

The only assurance that a restaurant won't discharge FOG to the collection system is to route all fixtures in the kitchen to a properly sized, installed and maintained grease interceptor.  By all fixtures of course I mean ALL FIXTURES.  Floor drains, floor sinks, three-compartment sinks, vegetable sinks, prep sinks, food grinders, dishwashers, mop sinks, woks, soup kettles, trench drain, bar sinks and even washing machines.

If the fixture is in the kitchen or bar area it needs to be routed to a grease interceptor.

It is possible to install an AGRD inside of a vault so that more fixtures can be routed to it, but then you have to make sure the device is certified to handle the extra flow rate; not all are.

Also, once the device is buried in a vault, the vault must remain unobstructed so that it may be opened at anytime by staff to maintain the collection container.

There is one other teeny, weeny, itsy, bitsy little problem to consider.


One of the most common complaints regarding AGRDs is odor.  Apparently heating up the contents to keep the FOG liquified also enhances its pungent smell - creating a kitchen atmosphere of loathing and disdain for the device creating the odor. 

The universal solution to this problem appears to be to unplug it.  Jurisdictions across the country report finding AGRDs unplugged in local restaurants.  When asked why the device is unplugged, kitchen staff invariably cite the raunchy odor.

You don't have to believe me, feel free to go into any kitchen that has one of these devices installed and smell for yourself.  That is if the thing is plugged in.

If it is not plugged in, feel free to plug it in for them while pointing out, "hey you know this is supposed to be plugged in to work properly, right?!"

Then run.

Does this mean that there isn't any good application for an AGRD?


In fact I am a believer in their application for rotisserie chicken oven's, for example.  These ovens can crank out hundreds of pounds of liquified chicken fat in a week - way too much volume for a typical passive grease interceptor. 

There are probably many other industrial cooking applications that these devices would be perfect for.

But, as a primary grease interceptor for a restaurant receiving the discharge from all the fixtures in the kitchen, I'm dubious to say the least.


  1. We have around 80 of these GRD units in our city and they are a headache for me as an inspector. The main problem is the human factor. I find units not being maintained properly or as you stated "unplugged". I feel like a baby sitter. I have even held training classes for each brand allowed and made it mandatory for a represenative of each restaurant to be present. The training helped but it is still a nightmare.

  2. All restaurant equipment including stoves, sinks, microwaves, refrigerators, and ovens not maintained will not work properly. AGRUs, passive grease traps and interceptors are no different. The odors from a passive grease trap do not compare with an AGRU. The passive traps win the rancid odor contest by a mile.

  3. I operate 50 restaurants in the North East. If you think AGRUs are high stinkage how do you rate a conventional grease interceptor. We are still trying to come up with an appropriate word.

  4. Great comments, thank you. Of course a passive grease trap will take on a very rancid odor due to the decay of its contents over time and of course the longer you go the worse the smell gets. Exacerbating the problem is metal interceptors with failing gaskets (rust is not easy to stick to) which invariably allows the internal odors to invade the kitchen. Point source interceptors are just not a good idea, whether passive or automatic, in my oh-so-humble opinion.

  5. How do you rank passive AGRD's like the Goslyn which have no moving parts compared to the wheel and skimmer models such as Greasestopper and BigDipper? I have seen several skimmer models that have had the guts ripped out.