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Dishing It Up

Dishing It Up

Every operator should understand dish machine basics since they are a critical part of almost every operation.

The dishwasher is probably the single highest utility user in your restaurant. In many kitchens it uses more electricity and more water than any other piece of equipment. Aside from operating energy costs, the item's initial expense is probably the highest of any item in the kitchen, too. They are also likely to be one of the more unappreciated appliances in your kitchen — at least until there is a problem.

The dishwasher purchase decision is an important one as it may well be the most expensive single piece of kitchen equipment you ever buy. You'll spend $10,000 for even a small, full height single rack machine that would be suitable for a restaurant with up to 100-120 seats. Larger operations generally need a rack conveyor machine, typically costing up to $20,000 and more.

After you add a clean dish table, soiled dish table, final rinse booster heater, and a few dish dollies and racks, it is not uncommon to spend $50,000 or more, and in high-volume noncommercial operations, sometimes well over that. With investments this large, it pays to have a basic understanding of what is available on the market.

Undercounter Models

There are four basic types of dishwashers typically used in foodservice. Very small operations may be able to use an undercounter machine with a typical washing capacity of about 40-50 full place settings per hour. These are often limited to washing china, glasses and flatware and are not well suited to production work because the ergonomics of bending and lifting make them inefficient.

Although a commercial undercounter dishwasher looks, at first glance, quite similar to a residential unit, they are much more powerful and faster. Their cycles vary from the slowest machines that use just over three minutes to the fastest that are around 90 seconds. Do not try to use a domestic model in your commercial operation because it will not meet the strict sanitation codes required. Also, when these machines are specified, remember that most local health departments require separate clean and soiled dish drain boards, separated to prevent cross contamination.

Single Rack Machines

The next step up is the door type or full height single rack machine. These typically have a footprint approximately 24" square, wash and rinse a rack of dishes in a little over a minute and can process about 90-110 place settings per hour. Over the last few years many manufacturers have paid attention to the tight space constraints of the small to mid-size restaurants that use these and have begun to offer final rinse booster heaters and controls mounted within the the machine's footprint.

The typical door type machine unit delivers a tremendous amount of washing power, some pumping over 150 gallons of recirculated water over the dishes during the short wash cycle. The machines being made today also conserve water using only, in many cases, 1.2 gallons of fresh water per cycle. Most manufactures make their door type units in either a straight through or a corner configuration.

Rack Conveyors

Rack conveyor machines, the type that process dish racks continuously, are available in a wide range of capacities and range in size from 44" to about 10'. Most manufacturers make a wide array of conveyor machines based upon different combinations of standard modules. All machines start with a basic wash tank and then add other modules depending upon the specifics of your operation.

For example, most manufacturers have one or two different pre-wash modules that are very effective for scrapping and removing heavy soil from dishware. Using a pre-wash reduces detergent use by not introducing it until heavy soils are removed from the china. A pre-wash unit typically adds about $6,000 to the price of a basic conveyor machine, but is a significant aid in getting especially those dishes with heavy soil clean. The next step up to higher capacity and better performance is the addition of a rinse tank or an extended wash tank. Flight machines, a fourth type of machine designed for very high volume operations (see sidebar), can be customized even more fully.

Decoding Manufacturer Ratings

When you look at machine capacities you need to understand and decode the manufacturer's ratings. Most advertise the capacity of a machine by the number of racks per hour it can handle based on its NSF (National Sanitation Foundation) listing. While the ratings are not meant to deceive, they do represent theoretical capacities. A typical rule of thumb is that the actual production of a machine in racks per hour is about 70% of the manufacturer's rating.

In other words, if a machine is rated at 200 racks per hour you should expect to be able to wash about 140 racks per hour (assuming you have a constant volume of dishes to be washed.) The same is true for those who claim a capacity of dishes per hour, although those capacities may be even less realistic because they are usually based on a relatively small dish or glass size that fits a 20" × 20" rack perfectly.

Using low temperature machines that employ a sanitizing chemical in the final rinse rather than 180° F water is one way to save on hot water costs and reduce some ventilation requirements. Chemical sanitizers clearly have a place in the market, but they are not for all operations. You must compare the cost of using the sanitizing agent a to your expected savings in energy costs to make an evaluation. Also, be aware that a benefit of the high temperature final rinse is quick drying of dishware. High temperature machines are also better able to break down grease on glassware and dishes.

In recent years, several manufacturers have developed machines that reduce water consumption by 30% to 60% over their own older similar sized machine. The machines save water by changing the size of the water droplets in the final rinse portion of the wash.

Using a different size water droplet significantly increased heat transfer to dishware, aiding in sanitation and in the process reducing water consumption. Sensors to shut down wash and rinse pumps are now an almost universal energy saving feature standard in many machines. (Another one to consider is water tank and door insulation which helps retain heat.) If you have an older machine, these and other energy-saving geatures may help your case for getting a newer replacement.


Dan Bendall is a principal of FoodStrategy, a Maryland-based consulting firm specializing in planning foodservice facilities. He is also a member of FCSI (Foodservice Consultants Society International). Bendall can be reached at [email protected]

When the challenge is high volume

Flight machines are designed specifically for high volume operations like large institutions and casinos. They differ from other types both in the throughput they can handle and the way they are loaded: rather than using racks, soiled items are placed directly onto pegs built into a conveyor that moves continuously through the machine. As a general rule, flight machines become an option when an operation uses china or other permanent ware for at least 500 meals in a meal period, especially at peak times (such as a catering event).

Flight machine construction is modular and units are sized and optimized for a given operation. There are three key choices to keep in mind:

The length of the load-in side of the conveyor. In especially high volume operations, length can facilitate loading by more than one person.

The length of the offload side. A longer exit track can improve drying time, especially if you use a lot of plastic trays and similar items which air-dry more slowly. If a lot of plasticware is used, another option is a blower-dryer on the exit. The trade off is that these increase the first cost and operating costs of the machine, so if you mostly use china, a dryer may not be worth the expense.

The number and size of the tanks in the pre-wash, wash and rinse stages of the machine. These are sized by the amount of soil you expect on dishware. In general, a pre-wash stage will tend to save money over time by reducing the amount of detergent needed in the wash stage. Also, depending on the speed at which the machine will operate, the length of the final rinse section will vary.

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