Dishwasher Pre Wash

[Chetlaham]

So yesterday I opened my Maytag during the pre-wash and their was a stream of "soapy" water running out and down the detergent dispenser. Which got me thinking. How essential are pre-washes?

A lot of older machines had 3 or more prewashes and typically two rinses. GE had 3 rinses, Whirlpool often had one rinse with a post main-wash purge.

Later machines seem to be ditching pre-washes and adding more rinses. I remember the 2002-2006 Maytag tall tubs had one or two pre-washes, but added 5 or more rinses depending on the soil level according to the tech sheet. My maytag at most has done only one pre-wash, but I've noticed 4 or more rinses on average. Tech sheets of newer machines (excluding Frigidaire) indicate the same- less prewashing more rinsing.

For those who don't know my terminology goes like this:

Prewash- any fill and drain BEFORE the main wash

Mainwash- the cycle where the detergent cup opens.

Rinse- and fill and drain AFTER the mainwash.

I know people think of rinses as anything without detergent (a prewash could be called a rinse) but thats not what I have in mind.

With that said, can dishwashers even successfully skip the pre-wash altogether and just tag along 4-6 rinses?

 

[murando531]

I use the exact same terminology when talking DW cycles. A Prewash is always the quick washes before the main wash, because to me calling it a "prerinse" doesn't click right seeing as how the water is going to be dirty and possibly have detergent as well. Then comes the Main Wash, then how ever many rinses, then the Final Rinse. The terms Purge and Eco Rinse come up too sometimes when talking with fellow washer fanatics because of newer machines being designed with clever ways to flush the filters clean without a full fill charge.

Purge, for example with Whirlpool machines, is like what the PowerCleans do after the main wash on the Normal cycles, filling with enough water to surge through the filter assembly and arms for a second or so before draining. The Voyagers and GlobalWash machines also do this before the main wash on certain cycles and sensor readings. The GWs I've had have been known to do two of them back to back after the main, and very often in between the prewashes as well.

Eco Rinse is still a "purge" but with slightly more water. The GlobalWash platform is the first I've known in WP's designs to do this, but it involves filling with about half the normal fill charge, and running the pump for a few seconds at a time, which causes just enough of a surge of water through each arm or arms to spray for a second or two at high pressure and rotate slightly before surging on air, pausing for about 15-20 seconds inbetween, and it does this repeatedly for several minutes, so that by the time it drains, the whole load has been sprayed down at least once from top to bottom. Then follows either another full rinse or final rinse.

Interestingly, the new house we moved into a few months ago had a 2006 PowerClean installed, which I tried for a day or two before replacing it** with my TOL 2004 PC. This slightly newer model isn't changed at all except that the Heavy cycle defaults to a prewash, 135F main wash, but then in place of the normal purge, it actually does something more like the "Eco Purge" where it fills with a bit more water and runs the pump for a minute, with the water surging and cavitating just enough to spray a bit at a time through the arms. It's the first PowerClean I've ever come across to do this, and only on Heavy. The Normal cycle would still use the traditional purge behavior. (**The existing one just hadn't been taken care of and because I have two immaculate machines already, it doesn't make sense to invest time in restoring a third one so my plan is to part it out.)

 

[murando531]

Moving on to the subject of prewashes being necessary, I'm probably about to blaspheme in everyone's eyes because prewashes to me are overkill in 99% of dish loads. Drag me through the dirt I guess, but the idea of filling a dishwasher full of dirty dishes, then setting it to its roughest longest hottest cycles just takes the fun out of how the machine works, *especially* on older dishwashers like the PowerCleans and old school KitchenAids. It's interesting that we all agree that manually rinsing dishes clean before loading them is just wasteful and silly, and yet running a Pots&Pans cycle with two full detergent cups full practically does just that, because after those 2-3 prewashes, (in most cases HEATED prewashes) those dishes are spotless before the main wash even starts. As a result, that main cup of detergent is popped open to barely any food residues at all, which seems to me to cause the same problem as people who scrub everything clean before loading and then complain that their racks are corroding away or the motor seal has etched away and caused water to ruin their nice floors.

Prewashes in a cycle seem even more unnecessary when considering that modern detergents actually perform best with food soils to activate them. I've washed more loads than I can count that were filled with dishes covered in sauces and dried goop and the door and tub bottom completely covered in drips and splatters, and after just a Normal cycle in the PowerClean it's all spotless, and that's with going straight into the main wash AND a purge before the final rinse! *gasp*

One thing I will add to be fair is that with the shorter wash cycles of the PowerClean and older machines, because I know for sure it's going to start with the main wash, I'll drop the detergent pac in the bottom of the tub and just close the cup to get that satisfying pop when opening the machine when it's done. That way the pac is already dissolved or almost dissolved during the fill before the wash action starts. Otherwise the detergent actually doesn't dispense until 6 minutes in, and the whole main wash is 12 min, which worked fine in the days of phosphate Cascade powder, but I like knowing my Platinum pacs today are getting the full time. Since doing that, I've never had anything after a Normal wash in terms of specks leftover or residues or odors.

This all is not to say that one prewash isn't sometimes useful in a super heavily soiled load, but I think one is plenty. That's all the PowerClean will do when set to Normal with Hi Temp Wash selected, and it's just a six minute prewash to sweep away the loose excess but not enough to take away all the soil before the main. I never actually use the Heavy on my machines and haven't even touched Pots&Pans because they both have thermal hold prewashes, and that's just... too much energy and water for no reason.

 

[iheartmaytag]

In my head

And probably no one else's, I have viewed the pre wash as purge wash of sorts. It helps to start loosening the soil that is more easily washed away, as well as it serves to start heating up the tub and dishes so the main wash will be hotter and detergent more effective.

This may be able entirely wrong, but I justified it that way when I used to lay in front of the Mobil maid and listen to the wash action.

 

[rp2813]

I think Andrew has made valid points about machines pre-washing vs. pre-rinsing by hand.  I never use the pre-wash cup in my Miele.  It's not necessary.

 

Disclaimer:  Since it's just me in the house most of the time, I use the rinse/hold option as needed.  Usually this happens when there's soil on the dishes such as egg residue that could dry and harden.  Without fail, after I run the rinse/hold, the dishes look sparkling clean.  This after just a few minutes of run time with water that the machine hasn't even heated.

 

When adding the last items that will fill the machine and call for a full cycle, I scrape but don't pre-rinse so there's soil for the detergent to work on, I run a "normal" cycle and only use the main wash detergent dispenser.  Never a pre-wash no matter how much soil, such as a BobLoad after hosting a dinner party.  Without fail, contents come out sparkling clean. 

 

As far as modern day well-designed dishwashers are concerned, there is no need for a pre-wash IMO.

 

[Chetlaham]

I agree, never pre-rinse.

And yes, per washes warm up the machine.

All good replies, keep em coming!

 

[gelaundry4ever]

My kenmore

will do a pre-wash, main wash, first rinse, final rinse then heat dry on the cycle I use all the time. Mine is great about making sure all the detergent is rinsed off and rinse aid evenly distributed through.

 

[Chetlaham]

You have good tastes in appliances GELaundry4ever.

 

[henene4]

I think pre-rinse is coming from our side of the pond.

When DWs were new our washers often as a standard still ran a pre-wash with detergent.
So for us, everything with detergent is a wash, everything without a rinse.

Thus pre-rinse.

Anyway...

Over here a lot has changed since DW filters became actually really fine and thus cought a lot of dirt quite well.

Most up-to-date design from what I see are ultra fine wavey filters.
That waveyness adds a lot more surface area and thus more filtering ability before needing back-washing.

Most eco cycles here don't do a full pre-wash anymore.

Either they don't at all or they do a cheat pre-wash (actually the latter is far more common, especially with variable speed pumps).

They cheat by filling with a larger (or rather normal), often sensor based amount of water and run a pre-wash at normal pressure.
Then, depending on conditions, they run the drain pump for a calculated amount of time (2-10sec, depending, from my experiece) and without refillign start the low rpm main wash.

Less water means higher detergent concentration and less energy to heat up.

But Auto-cycles have become verry accurate as well.

Our Bosch in the old flat tended to run a full pre-wash, medium or low stregth main wash, full rinse and final rinse.
Never did it run its theoretical full load version.

Our slimline Bosch back home tends to not run a prewash, therefor a more intensive main wash.

My Miele here is all over the place.

That is the first EU machine that I know that does the eco-rinses (always on Eco, sometimes on Auto) and whose energy usage is quite variable (first I can actually observe due to eco feedback).
Part of that is the sensor drying, part of that is "guided energy usage", part if that is on point load sensing.

The Auto cycle supposedly goes from 6l to 13l and 0,6kWh to 1,2kWh IIRC.

I've seen it peak at 14l and 1,4kWh - it has an option that allows the machine to calculate when it would be beneficial to run a hotter final rinse plus higher water levels if temperatures have been to low during to many cycles.

Basicly automatic maintenance included in a normal wash.

Worst case would be slightly higher actually if the water softner regeneration, hygiene rinse and high soil load would coincide.

Lowest I have seen was 8l and 0,7kWh on a low soil run.

But I have seen low water usage with up to 1.1kWh as well and high water usage with lower energy usage as well.

 

[gelaundry4ever]

To chetlaham

I appreciate it.

 

[lakewebsterkid]

Pre-Wash

I had a nice long post, but it did not post.
However, I use the Auto cycle on my Bosch specifically for the pre-wash.
But, in a machine that has a food chopper it isn't as necessary.

 

[jerrod_six]

USA Miele DW

I have a Miele 6987 and for the Normal cycle, the majority of the time the prewash water is used for the main wash also. According to the app on my phone, it takes about 1 gallon and uses that for the Prewash and the main wash. The first rinse uses .7 gals, and the last uses .8 gals. I wash 2-day old dishes that have been sitting unrinsed and the Normal cycle cleans them well.

On the Normal cycle, the prewash always lasts 18 minutes and the main wash is usually 36 min. I measured the water temperature of the wash once and it was 132F. Whenever it does change the water for the wash, it results in a wash of about 60 minutes, but this rarely happens.

Pots and Pans use 1 10-minute prewash, followed by a water change, a wash, and low water level rinses.

So it seems like for this dishwasher a Prewash with a water change is not important unless the soil level is high.

 

[lakewebsterkid]

Prewash

So, our old Point Voyager would occasionally skip the pre-wash drain and go straight into the main wash using the same water. It could perform an AFP and remove some of the junk from the sump before starting the wash.
With that being said, I would much rather have purchased a Global Wash machine that would have performed 1 pre-wash, main-wash, and 2 deep rinses. But I did not have control over that. Lol.
I will say, that our Bosch will perform 3 pre-washes on the Heavy cycle when a high soil level is detected. The third pre-wash is actually heated and removes a lot of crap.

 

[jerrod_six]

lakewebsterkid

What model Bosch do you have and when was it purchased?

 

[iiijohnnymaciii]

I believe that a prewash is important. Particularly a quick unheated one.

I’ve noticed that machines that start with a quick prewash do a great job of keeping Tupperware from getting stained with red sauces.

The quick prewash does just enough to get most of the red sauce out of the dishwasher so that when the main wash happens, the wash water isn’t saturated with red sauce and plastics are much less likely to get stained.

 

[cam2s]

I probably tend to use a more aggressive cycle than what I need but I always like a prewash. My Bosch if you used normal could decide to skip the prewash or not, it usually would always add one in. I usually used power scrub which forced a heated prewash, sometimes with really mucky loads it would add in another. My old school Potscrubber that I’m using now uses 3 prewashes on Power Scrub and Normal/Heavy soil and 2 if you use normal/regular soil or China. Even though mine has the passive filtration system the extra fills are suppose to help flush soil out and also warm the interior, since it has a weak heater and calls for 140 degree water. One of these days I’m going to test the effectiveness of the filtration system and run a cycle where I skip the extra fills and run a WWRR program.

 

[lakewebsterkid]

Dishwasher

SHE863WF5N Jerrod_Six
I purchased it in February of 2018. I thought it was actually older.

IIIJohnnyMacIII, I agree with your statement!!

 

[iiijohnnymaciii]

Yeah, that’s the problem I have with my power clean. The prewash cycle is more than 15 minutes long and stains my interior and plastics. It doesn’t matter if I fill the entire prewash cup with bleach based detergent or not. I wish there was a quick 3-4 minute prewash like my old kitchen aid had. Nothing ever stained.

 

[murando531]

15 minute PowerClean prewash

On what cycle? The only cycles that have any sort of long prewash on the latest year PowerCleans (since 2002-2009) are the Pots and Pans/Antibacterial cycles, depending on the model. The Heavy cycle has just a quick prewash before the heated main wash. Normal goes straight into main wash, which when paired with dropping a detergent pac into the bottom of the tub and not going crazy with adding extra to the cups, does perfectly for anything except scorched/baked on soils. The Normal cycle on its own always heats the water for the 12 minute duration, and dropping the pac in allows the fill to dissolve it before the wash action ever starts so you get the full time with detergent and enzyme cleaning.

Adding Hi Temp to a Normal wash will give you a similar 6 min non-heated prewash, then a 135F temp hold main wash, which is the most I've ever had to use for a PC, and it's mainly for super heavily soiled loads with dried on foods that have sat for a day or two. The Pots and Pans cycle, and adding Hi Temp to anything other than Normal, is just overkill and guzzles extra water, because the dishes will be clean before the detergent cup ever opens and at that point it's just eating away at the rack coatings and seals.