Dishwashing | My Business | Mississippi Power | A Southern Company

Dishwashing

One of the single most important food service functions that creates a strong customer image (positive or negative) is the visible cleanliness of dishes, glassware, and silverware. The proper design, operation, and maintenance of this dish washing or ware washing capability is essential to the financial performance of commercial cooking establishments.

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While the dishwasher is obviously the core of the design, proper dish washing area ventilation is essential to controlling humidity levels for employee comfort, safety and effective ware drying. In addition, adequate lighting enables workers to perform their cleaning tasks more easily. This avoids potentially unsafe situations with broken glass and dinnerware, as well as alerting them to any water accumulation on floors. Finally, adequate electrical power and water pressure are critical to the performance of many dish washing systems.

A wide variety of dish washing equipment is available on the market. The model that best suits the needs of any one food service establishment largely depends on the menu and the number of meals served. Other factors include:

  • Bussing methods
  • Number of utensils used per table setting
  • Duration and frequency of meal time peaks
  • Waste disposal and pre-washing methods
  • Clean dish storage capacity
  • Organization of dish-room labor
  • Local health codes

Time management is also paramount, since ineffective dish washing system problems can bring food service operations to a complete halt.

Finally, dishwashing areas, by their nature, are very noisy. Therefore, special attention should be given to incorporating noise-reducing materials in floors, walls, and ceilings of the dish room. Bussing, scraping, racking, dishwashing, and ware handling noises should be constrained to within the dish room to the extent possible, with special attention towards avoiding disturbing patrons. We will discuss three basic types of dishwashing equipment. They are:
  • Single tank or under-counter
  • Door type
  • Flight and conveyor-rack units.

Operation

There are four stages in the proper operation of a dish machine: scraping and pre-wash, wash, rinse, and final rinse/sanitization.

Pre-wash uses hot water sprays to remove easy grease and soil. Water temperature settings are a compromise between cutting grease and baking on certain foods. Milk, fruit juices, and dairy products are best pre-washed in cold water.

Wash is the backbone of the cycle where hot water and detergent are pumped through fixed and whirling nozzles above and below the dishes in racks or on conveyer belts. This action loosens and washes away the soil, trapping larger particles for disposal. Water temperature should generally be between 140° and 160°F to soften soils and melt greases. Lipstick removal requires temperatures in excess of 150°F. If the desired water temperature can not be maintained, detergent strength must be increased to compensate.

Rinse uses 160° to 180°F hot water to remove wash solution and any residual soils. The action is similar to the wash cycle but does not use detergents.

Final rinse and sanitization removes all traces of the wash solution with water temperatures between 180° and 195°F. These high temperatures have the added advantage of reducing drying times. A rinse additive is injected to facilitate water drainage "sheeting action" and to prevent water spotting during this quick-dry stage.

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Good dishwashing operation is a compromise between proper cleaning and operating costs. There are obviously tradeoffs between over-washing and under-washing. Water temperature, detergent concentrations, operating cycle times, water pressure, and even rinse additives must all be considered carefully.

Components

The basic components of a dishwasher are:

  • The water-holding tank
  • Racks
  • Spray nozzles and blades
  • Controls
  • Door and housing
  • Vents
  • Electrical power and water connections
  • Some units have additional components for special tasks. The most popular special component is the conveyor rack, for enhanced automation.

Types

Single tank under-counter dishwasher

The smallest capacity dishwashing equipment design presently on the market is the single tank or under-counter unit. This model is ideal for smaller establishments such as taverns and bars that generally serve no more than 100 meals a day. The under-counter model washes between 17 and 21 racks of dish-ware per hour and has a maximum water requirement of about 40 gallons per hour. Most under-counter dishwashers operate with a 2-and-one-half minute cleaning cycle. Remember, proper maintenance, adequate ventilation, correct water temperature, and full-load-operation each contribute to overall system efficiency.

Door type

Door-type, or stationary rack, machines are one of the most common types of ware-washers because of their compact size and versatility. They are used by small operations with fewer than 150 seats and can wash up to 60 racks of soiled dishes per hour. Door-type dish-washing equipment is best suited for facilities serving 100 to 200 meals a day. The maximum capacity for high temperature machines is roughly 65 gallons per hour. Most machines consume between 70 and 90 gallons of hot water per hour, while low temperature machines average 110 gallons per hour. This type of dishwashing equipment is designed to sit between two tables: a soiled loading table and a clean table on the discharge side of the unit.

These free-standing door-type dishwashers have a heated tank for storing wash-water at the proper temperature. Water circulates by means of a motor-driven pump through spray pipes or nozzles. These may be located above, below, or both above and below the dish-rack. This unit includes a cover, hood, or door. Fresh hot water from a separate set of nozzles located both above and below the rack provide the final sanitizing rinse. A typical wash cycle lasts about 45 seconds with an additional 12 second rinse cycle.

Conveyor rack

Conveyor-rack dishwashers come in one, two, and three-tank models and are capable of washing 125 to 360 racks of soiled dishes per hour. Racks that hold the dishes move on a continuous chain conveyor through each step of the automatic wash and rinse cycle. The operator simply loads the racks and feeds the machine with one rack after another.

In the lower volume single-tank machine, the tank holds the wash water and detergent mixture. Some of the rinse water, supplied by the booster heater, is then drained into the wash water tank. Double tank machines are designed to hold the wash water while the other tank holds the rinse water permitting much quicker washing cycles. Triple tank machines use another tank for pre-wash cycles to remove food. Blowers and heated dryers are available.

A two-tank machine has a detergent wash, a hot-water rinse, and a final sanitizing rinse. A three-tank machine includes a pre-wash cycle, eliminating the need to spray-rinse flat tableware manually. These machines are best suited for use in large capacity facilities, such as hotels, hospitals, colleges, and anywhere that 200 to 400 meals are served daily. The typical cleaning cycle lasts one minute, and, on average, these machines use about 415 gallons of water per hour. These figures vary by manufacturer, of course.

Flight type machines

Flight-type machines are also called "rackless" or "belt conveyers" and are the monsters of the dish room, capable of washing as many as 24,000 dishes per hour. They are the primary choice for large institutions.

They come in double, triple, and sometimes custom-built four-tank units. Double tank models are preferred for schools and similar facilities where the food is simple and the variety is limited. The two-tank machine consists of a wash tank and rinse tank. Three-tank models have tanks for prewash, wash, and rinse cycles. All flight type machines have a final sanitizing rinse cycle.

Ventilation for ware-washing equipment

Dishwashing equipment produces a large amount of steam and heat, which dissipates into the surrounding area, making the kitchen uncomfortable. A mechanical exhaust ventilation device installed directly above the washing machine can help control the level of steam and heat in the kitchen. General whole-room ventilation can also do the job provided it can sufficiently remove steam and excess heat in the kitchen.

Ironically, excessive ventilation can be detrimental to washing operations because power-rinse and final-rinse cycles require a certain degree of heat. A ventilation system that is too good, so to speak, can eliminate some of the required heat, making the drying processes virtually ineffective. On the other hand, mechanical ventilation tends to reduce the relative humidity of the room, which enhances air-drying processes, and makes the room more comfortable for employees. Make sure that you consider all the factors when choosing a ventilation system.

Efficiency

Saving money

The easiest way to save money with ware-washing equipment is to purchase insulated models with water saver units and then run the unit with full loads. Some machines do have efficiency management features, such as variable cycle controls for smaller loads, but most commercial dishwashing equipment is designed with volume in mind; it operates most efficiently under a full load. Frequent cycling with small wash loads wastes water, energy, and time. While the dishwashing equipment itself is obviously electric, most of the energy used in dish washing is in the form of hot water. Therefore, selecting the method of water heating, be it resistance, heat pump, heat recovery, or gas-fired, is an important related decision. Contact your local utility representatives to assess these options.