Fats Oil and Grease (FOG)

Oh, that wonderful smell of a dirty grease trap... FOG unfortunately is a problem most foodservice establishments must deal with in some form or another. It is a messy and often expensive side effect of food preparation that can lead to big plumbing bills and in rare circumstances legal woes for some restaurants. The key to dealing with it sustainably is by minimizing the creation of and maximizing the disposal of fats, oils and grease.

As with most any of other resource or product, reducing the amount produced or consumed is the first step in becoming more sustainable. More often that not, this involves changes in an establishments menu and making use of FOG best practices (see below). While FOG is a natural occurrence in food preparation, removing greasy foods, cream sauces and the likes from a menu can have a great affect on FOG waste. The next step is reducing the amount of FOG released into the municipal wastewater stream and recycling that waste. Grease traps and interceptors, which are mandatory in most areas, will save immeasurable money and hassle for a small investment in time and money. Any foodservice establishment without a grease trap should immediately install some sort of FOG removal system.

Losing the Grease - Menus and Fryers

Deep fat fryers are easily the biggest producers of FOG in a foodservice facility contributing to costs, labor and maintenance. Many larger cafeteria-style foodservice facilities in schools, hospitals and detention centers have removed fryers from their kitchens. Most have cited health issues in an epidemically obese America for removing the fatty fried food from the their menus, but have also benefited from a few other factors as well. The loss of a fryer has not meant changing their menus however. Many companies offer baked versions of French fries, chicken strips and most all other traditionally fried foods.

Fryers tend to be the most expensive piece of equipment in a commercial kitchen because of both the use and disposable of fryer oil and the substantial energy costs. Fryers are very inefficient in their use of gas or electricity. Standard gas versions only use around 35% of energy input to cook the food with the rest wasted energy. Energy Star units rate no higher than the mid 60% range. Electric fryers are more efficient with Energy Star units boasting 80%+ cooking efficiencies. Besides the high energy costs of fryers, are the costs associated with the purchase and disposal of fryer oil, the maintenance of the appliance and the additional labor of dealing with FOG.

FOG Removal - Grease Traps & interceptors

There are a number of different grease separation devices with varying degrees of technology used in the foodservice industry. These devices should be installed at every FOG producing area including prep, pre-wash, and mop sinks, woks, trash compactors and floor drains. Different regulators may or may not require grease devices on commercial dishwashers.

The most commonly known and used is the simple grease trap or manual grease separator. Grease traps refer to a device used inside a facility to separate FOG and solid material from wastewater via a system of baffles before it enters the waste-stream. These devices are normally used in restaurants, relatively inexpensive and easy to maintain, but must be manually cleaned on a regular basis to remove the FOG.

Another similar system is the automatic grease trap. These systems use different methods such as belts and skimmers along with a heating element to mechanically separate the FOG from the wastewater then remove that FOG into a separate container. They are more complex, expensive systems that require electrical connections, but can be very effective FOG removal devices. These systems are often configured with sensors and controllers that will signal when the system is full. Both larger restaurants and some non-commercial foodservice use automatic grease traps.

Facilities that produce a large volume of FOG usually install grease interceptors, also commonly called grease traps, outside the kitchen. Interceptors are large, often preferable containers of 1000 gallons or more buried at ground level outside the foodservice facility. They are often required in new construction and require less maintenance than manual grease traps, but need maintenance from a professional grease collector that pumps the FOG from the containers.

Sizing a Grease Trap

Proper sizing of grease removal devices by a professional plumber within local regulations is essential to proper FOG removal. Grease trap installation requires building permits and should only be installed by a licensed plumber. As with any other contractor, you also need to do your homework. There are a number of stories where plumbers installed the grease incorrectly, so make sure your plumber has experience with grease removal systems. Here are a few other things to keep in mind when installing a new system:

  1. Plan ahead, think about future growth and maximum capacity. A few hundred dollars up front may save thousands later in maintenance fees
  2. Consider your menu when choosing a system. A menu heavy in fried and saucy foods create a lot of grease. You may need a bigger trap than what the calculations say. Pizza places in particular produce a large amount of FOG
  3. Make sure devices are readily accessible. There is nothing worse than having to move pieces of equipment or storage racks every time the trap needs cleaning.
  4. Consider installing a solids strainer in-line previous to the a trap
  5. Work with contractors with experience in commercial kitchens

For those interested, the Plumbing and Drainage Institute created calculations based on sink dimensions to determine trap size. You will find the sizing info on page 16. PDI also created a simplified Basic-Principles for Sizing Grease Interceptors document.


Many companies offer "environmentally friendly" enzyme solutions that break down the FOG in grease traps and supposedly expel water with digested grease. While some of these enzyme products may be useful for cleaning tile or floors, they are not proven grease removal systems, can contain questionable ingredients and are not recommended for use with grease traps. Many of these enzymes do not 'eat' the FOG, but just temporarily separate the grease from the water, which then flows into the wastewater system and attaches to pipes downstream of the grease trap. In addition, many states and municipalities prohibit enzyme use for cleaning grease traps. In general, it is better to clean the grease traps on a regular basis.

Exhaust Hoods

For some reason exhaust hoods tend to be overlooked by wastewater people when it comes to FOG. Yet, they are designed to deal with grease and probably vent out as much grease as is passing through the dish room. A well designed and efficient hood is essential is a commercial kitchen and can help diminish the amount of FOG in and around the kitchen. Poorly designed systems let cooking exhaust escape into the kitchen along with the grease attached to the hot air. Routine and proper cleaning is also important for exhaust hoods. Excessively greasy hoods can leak grease into drains on the roof and into storm drains. Also, make sure your hood cleaner does not dispose of the grease from the hood into your dish or mop sinks. For more information on Commercial Kitchen Ventilation (CKV), see the HVAC link on this site and the best practices below.


One of the best things about collecting FOG, besides the reduced plumbing bills, is that the FOG can be recycled. There are two types of grease, yellow and brown. Yellow grease is the grease removed from fryers and similar cooking equipment. The waste grease haulers sell the yellow grease to rendering companies to turn into cosmetics, soaps, fertilizers and animal feed. Brown grease is the stinky glop removed from grease traps or any other grease that has come into contact with water. Brown grease is often thrown in the trash, but can be used to make paints and polymers or used as a co-fuel in incinerators.

Alternatively, a more localized and potentially personal use of yellow grease is in fuel. With the soaring gas prices and demand for a green, domestic fuel source, bio-fuel has become a booming, albeit, underground industry. With a small set-up, do-it-yourselfers can convert a restaurant's yellow grease into fuel for their diesel vehicles. The grease is either converted through a simple but messy process into bio-diesel, or used pure in vehicles converted to simple vegetable oil (SVO).

SVO users filter the oil through screens or a filtered pump directly into a second SVO gas tank on their diesel vehicles. The SVO tank contains a heating element that warms the oil when the vehicle is running. After the congealed oil is warm enough to pump through the engine, the driver can switch over to the SVO tank and run the vehicle completely on recycled fryer oil.

Best Practices

Taking steps to reduce the amount of FOG produced and to entering the wastewater stream will save on plumbing and grease trap / interceptors maintenance costs.

  1. When cleaning fryers squeegee the insides while still warm then wipe down with paper towels before cleaning. This will reduce the amount of oil going into the sewer system
  2. Train employees to dispose of liquid and solidified grease into a designated bucket for disposal into a grease dumpster for recycling
  3. Use dry clean-up techniques. Use spatulas to scrap grease and food material from pots and plates before pre-rinsing them. This saves time, water and helps keep the kitchen drains clean
  4. Use dry clean-up techniques for greasy spills. Use paper towel or absorbent pads before mopping
  5. Use sink and floor sink strainers
  6. Direct all drains from FOG producing sources to a properly sized grease interceptor
  7. Do not dispose of food waste in a garbage disposal. Disposals contribute to FOG in a municipal sewer lines and use an excessive amount of water. Instead, consider a commercial composting option
  8. Wipe excess grease off hood filters, then wash is a dish sink or sink where the wastewater will discharge into a grease trap
  9. Have exhaust hoods cleaned on a regular basis
  10. Make sure your exhaust hood cleaner does not dispose of the grease from the hood into any of the kitchen sinks
  11. Cover outdoor grease receptacles so water and grease cannot fill or overflow out of them
  12. Do not clean mats or any other equipment outdoors where the wastewater and grease can drain into the storm drains. (It is illegal in most areas)
  13. Keep the area around grease receptacles clean and use a dry cleaning method like absorbent pads to clean up spills. Do not use loose absorbent material like kitty litter, which will leave residual amounts of the material and grease
  14. Keep outdoor grease receptacles away from storm drains
  15. Post No Grease signs above sinks
  16. Do not dispose of caustic chemicals, acids or solvents into sinks or use these chemicals to clean a grease trap. Dispose of them according to local health codes. See earth911.com to find local disposal options
  17. Clean all grease removal devices on a regular basis. Many traps need cleaning on a weekly basis, but frequency will depend on the trap and your facility. Clean traps when the device's contents are 25% grease
  18. Keep a maintenance log of grease trap cleaning

Additional FOG Resources

Biodiesel Magazine

Grease Works Co-op
An informative site full of information and resources on biodiesel, SVO and diesel conversions

Plumbing and Drainage Institute Publications
This is a good resource for designers looking for more information on design, function, maintenance and sizing of grease traps.

Thermaco Inc.
Themraco is a automatic grease trap and interceptor manufacturer. Their web site contains a lot of information on grease traps, troubleshooting problems, maintenance, sizing recommendations and their products.

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