What Everyone Washing Dishes Professionally Must Know About Dish Machine Temperatures and Sanitizing

BY MICHAEL O'BRIEN, LAUNDRY AND WAREWASHING MANAGER

Michael has nearly a quarter century of experience in the foodservice and warewashing industry.

Kitchen staffers everywhere spend a lot of time keeping track of and documenting food temperatures. Proper cooking and storage temperatures, and the required record-keeping, is vital to passing health department inspections.

Water temperatures in your dish machine are just as important. Just like with cooking and food storage, sanitation depends on temperature and chemistry. However, dishwasher temperatures can be confusing. For instance, what exactly is “hi-temp” versus “lo-temp”, and how should you measure?

Let me shed some light to hopefully simplify. Hi-temp machines use hot water to sanitize your dishes, while lo-temp machines use chemical sanitizer products (almost always chlorine, although a few use iodine) for the job. Although they depend on chemistry for sanitizing, lo-temp machines still have temperature requirements. Minimum wash temperature on a "purpose-built" lo-temp machine is 120 degrees. However, you will get much better results on greasy dishes if your water temperature is at least 135 degrees.

Most lo-temp machines use the same hot water that comes through the taps in the rest of the building, which leads to a problem: do you crank up the water temperature in your building heater to 140 degrees to get 135 degrees in your machine? This could lead to people washing their hands in uncomfortably hot water in the restrooms. As an alternative, many facilities keep the water around 125 degrees and devote more effort to pre-washing.

Yet another option is to add a booster heater at the point of cleaning. This is a separate water tank holding 3-5 gallons of water built right into the machine or located next to it. They are used to heat the rinse water on all hi-temp machines. It seems counter-intuitive to have one on a machine called “lo-temp”, but getting the temp up to 135-140 degrees from 120 isn’t that expensive in energy terms, and it does make a difference in results.

TIP - Make sure you don’t crank the temperature up too high — the chlorine sanitizer in a lo-temp arrangement becomes unstable and “off-gasses” above 150 degrees.
Fast Fact: Lo-temp machines require more careful pre-washing than hi-temps to get good results on glasses and silverware, and the dishes take a little longer to dry. On the other hand, they cost thousands less than hi-temps to purchase, use way less electricity and water, and are easier and cheaper to repair. You have to decide what the best fit for your facility is.

Lo-temp machines drain the wash water and fill up with fresh water for the rinse step. Wash and rinse water are held in the same tank, and this makes it simple to check the temperature. All machines come with temperature gauges, but it is a best practice to cross-check them with a hand-held thermometer once a day and enter the data in your log to show the health department. Laws also vary by state and locality.

Stop the machine during the wash or rinse step of the cycle, wait for the water to subside, and then stick a meat thermometer into the tank. 120 degrees is the minimum temperature, and it shouldn’t be over 150 degrees.

There is a small sub-set of lo-temp machines - hi-temp units that have been converted to lo-temp operation by the addition of a chemical pump. The rinse water booster heater is often removed as well. These machines should have their lo-temp operation water temperature requirements listed on a panel or sticker, and vary somewhat by manufacturer.

Fast Fact: No matter what the company that built it says, converted lo-temps don’t work as well as purpose-built ones, and the introduction of corrosive sanitizer into the rinse system often causes multiple service problems.

GETTING INTO HOT WATER

Hi-temp machines use hot water to sanitize the dishes instead of chemical sanitizer. Unlike lo-temps, hi-temp units have a separate rinse-water source and use fresh, hot water that has been heated in one of the booster heaters mentioned above to the proper temperature. That sounds simple enough - but of course, it isn’t. What did you expect?

The health department wants the surface temperature of the dishes sent through the machine to reach 160 degrees for 10 seconds. Experience has shown that heating rinse water to 180 degrees as it enters the machine will produce 160 degrees on the dishes. The problem is that your booster heater temperature setting depends on how far it is from the dish machine, what size the pipes are, and whether they are insulated. Most boosters are set from 188 degrees to 195 degrees, but yours could be different. The key is that it must be 180 degrees as it goes into the machine, and a little higher than that is optimal.

Fast Fact: If your booster has trouble reaching the proper temperature, don’t keep turning it up. Try buying pipe insulation foam tubes from a home improvement store and wrap all the pipes from the booster to the dish machine. You can cut heating requirements by as much as 5-8 degrees.

Your machine has a built-in rinse temperature gauge that takes readings from a fitting in the rinse pipe. Many health departments require that you cross-check this temperature daily and record it, and I recommend doing that whether it is required or not. The question is, how?

Most people, including health department inspectors, use the pass-through method. You can purchase special water-proof stickers or paper “temp sticks” that you put on a plate or tray and then send through the dish machine. They change color if the proper temperature is reached, and can then be removed and stuck into a log book with a date as proof of compliance. The other method is to use a “holding” thermometer, which is an electronic or mercury thermometer designed to “stick” on the highest temperature reached until it is re-set or shaken down. You put one of these on a rack with something heavy on it to hold it down and send it through the dish machine. Then record the temperature in your daily log.


PASS-THROUGH PROBLEM

There is a big problem with the pass-through method, however — it is not accurate. Why not? Well, the wash tank temperature on hi-temp machines is a minimum 150-160 degrees. It is common to see units running a wash temp of 165 degrees or higher. If you send a thermometer or sticker through the machine to see if the rinse is getting to 160 degrees and the wash tank temp is already 162, you aren’t reading the rinse temp. It could be 140 degrees, but the color changes on the sticker, or the thermometer reads 162, because that’s what the wash tank temperature is.

A BETTER WAY TO CHECK TEMPERATURES

You have to expose the sticker or thermometer directly to just the rinse water. On a single-rack machine, you to run the unit until the rinse cycle starts, then stop it, put the thermometer or sticker in, then continue the rinse cycle. Some machines have a button or switch that allows you to manually run the rinse without a wash step.

On conveyor machines, you have to take down the rinse curtain and place the thermometer or sticker into the rinse spray when it comes on. I recommend using some kind of tool to hold your measuring device, as 180 degrees is quite hot.

Okay, so now you’ve burned your fingers, but you have your rinse temp. Job well done, right? Not yet. You need to check the wash tank temperature as well. Fortunately, this is much simpler. Run a few racks through the machine, then open the door and stick a thermometer into the wash tank reservoir. Now you’re finished.

Fast Fact: Why is wash tank temperature important if the rinse water kills the germs? Because reaching 160 degrees on the surface of the dishes is much easier to do if the wash tank water heats them up to 140-150 degrees first. You shouldn’t run the machine if your wash tank water drops below 150, no matter how hot your rinse is. Get it fixed ASAP.

RINSE WATER PRESSURE IS CRITICALLY IMPORTANT, TOO

We’ll close on a related issue, rinse water pressure. All hi-temp machines will have a sticker or plate on them somewhere that says that the rinse water pressure must be between 15-25 PSI. Some will say, “20 PSI, +/- 5”, which means the same thing.

Why is this important? I asked one manufacturer about this, and was told that if the pressure is too low, the water comes out in thick streams that will not cover every inch of the dishes as they go through, leaving hard-to-reach places unsanitized. If the pressure is too high, the spray turns into a mist that is too fine to raise the temperature, much like the misting systems used in backyards and outdoor restaurants — even if the water in the hose is warm, the resulting mist produces evaporation that cools off the surface it lands on. That’s not the desired effect inside a dish machine.

Make sure the rinse pressure gauge on your machine is functional, and make sure it is in the proper range, whether your health department inspector brings it up or not. 18 PSI is the optimal pressure. 

Now, you're ready to monitor sanitizing and temperatures like the pro that you are.