Prewash-less Dishwashers

[Chetlaham]

Another thread got me thinking. How necessary are pre-wash cycles with modern dish-washing detergents and longer main wash times? How practical would it be to eliminate the prewash sequence altogether?

 

 

I've noticed modern dishwashers in general have fewer pre-wash phases and more post main wash rinses compared to machines 30 years prior. 

 

 

I'm thinking of a cycle sequence like this- either on a modern machine or on a Whirlpool Power Clean Module, Maytag Reverse Rack or a Hobart Kitchen-Aid.  

 

 

 

 

 

Second Variant:

 

 

 

 

Main wash, final rinse and heated dry are all heated.

 

[henene4]

One reason the US tends to be more prewash friendly is hot fills.
You gotta assume most people don't purge lines before starting the DW, so even if a prerinse is cold, that purges the lines making the following main wash more of a hot start.

But in general, cycles without prewashes were pretty common in the EU since the 90s, mainly Miele had them on many of their "Universal" cycles.

One reason for prerinses is to get rid of colored foodstuffs, like tomatoes or currys or such.
Those can easily stain plastics in a hot main wash.

But many Eco cycles today just don't have them and still perform really well.
BSH (Bosch) over here are actually one of the holdouts for a kind of prerinse on their economy cycle. That cycle does a dynamic partial drain and refills if necessary to get rid of some stuff before the main wash starts.

Sensor cycles are of course another story.
There discussion comes even down to heated vs not heated prerinse and stuff like temperature rise load sensing in the prerinse.

There are certainly a lot of scenarios where a prerinse makes since, a lot where it isn't needed and more and more where you don't even have to worry about that and let the machine decide.

 

[qsd-dan]

I'll pass.

Give me a pre-wash to knock the big stuff down, drain the dirty water, and commence washing again.

I wouldn't want the same dirty water cycling for hours at a time....although that kind of happens with todays dishwashers. At least there's still a pre-wash.

Don't be giving the EPA or corporations any ideas, Chet. Things are already bad enough, lol.

 

[Chetlaham]

Those EU dishwashers that skip the pre-rinse a find very interesting. How are the post wash rinses? Are there more or less rinses than before? I tend to think that with more detergent in the main wash one can skip the pre-wash provided there is an extra final rinse, but for very dirty backed on pans/broilers I'd think that would not be enough.

 

 

Dan, you have point. For really greasy stuff there just wouldn't be enough water and detergent to get everything clean. 

 

 

[lavamat_jon]

It really depends on the load. For anything that is burnt on or with tomato sauce residues a prewash is necessary. I also find it useful when the coffee machine drip tray and waste container are in the load (or a cafetière) to prevent coffee grounds being redeposited - but this can be overcome with two interim rinses before the final.

I use the auto cycle generally and let the machine decide for itself. Our Siemens IQ700 will do 1 to 3 rinses between the main wash and final rinse on auto, depending on how dirty the load is. The Shine & Dry option forces 3 rinses, whereas the variospeed option will force a prewash.

Eco doesn’t do a pre rinse on ours, unusual as most BSH dishwashers at least purge if not fully drain as Henrik mentioned on the eco cycle. I find the eco cycle lacklustre personally for most loads with any soiling, so don’t particularly bother with it.

If there is nothing particularly challenging or heavily soiled, I will use the speed 60° cycle which performs a wash, 2 short rinses, and a final rinse with good results on an everyday load of crockery and lightly soiled cookware

We had a mid 2000s Miele G975SC for a year or so to tide us over before the Siemens, and that didn’t prewash on the Universal or Intensive programmes to no detriment on most loads. For loads that needed a prewash, I would select Universal plus and that would clean everything.

 

[qsd-dan]

I snapped this up from a the pre-wash load I just started in the Point Voyager. The picture makes the water appear cleaner than it actually is. I think the pre-wash cycle is about 5 minutes, I'll have to time it on the next load.

 

[gelaundry4ever]

my Kenmore

My Kenmore does a pre-wash at normal pressure, then a second prewash at full pressure on smart wash HE.

 

[Chetlaham]

What is the water charge on that prewash fill? I am with you, I have to admit, I'm not sure I can stomach that going around for 45 minutes. Even with  more detergent and a 2.5 gallon water charge I'd feel better with a pre-wash. 

 

 

@jon- Whats interesting is it seems that sensors and cycle selection tend to vary the number of post main wash rinses more than they vary the number of pre-washes. I'm guessing they rely on these rinses for soil carry away once everything has been washed off the dishes.

 

[lakewebsterkid]

No prerinse /prewash

Could it be done? Absolutely. A lot of newer machines default to it on Normal cycles. It does save a decent amount of water. However, there could be a way around that. But, this is highly variable depending on soil level, design of machine filtration, time of cycle, etc.
The AFPs on the Point Voyager immediately came to mind. The Normal cycle when No-low soil sensed would skip the prewash and go directly into mainwash after the 10 minute prewash phase occurred, but heavy soils would trigger the AFP to drain heavy soils out of the “filter”, then would refill and wash for a second before draining to proceed into main wash. Normal soil or High Temp wash option on always defaulted to drain prewash without mandatory AFP. However, that was changed on newer models where an AFP would be performed to try and clear some of the soil before performing a full drain. I believe 3 AFPs could be done. This is actually a better idea and makes far more sense to me to prevent a full drain, but as mentioned before, a load with red sauce can cause issues with staining. Though, sensors now should be advanced enough to prevent this issue from occurring and trigger a prewash.
Even a no-low soil cycle in the Point Voyager would still use ~4.6 gallons on the older machines. The issue we had was too short of a wash cycle, redeposit city, and poor rinsing. I know the machines could do an AFP at the end of the wash cycle if needed to improve rinsing, but was not default. Ours could have benefited from it being standard. Though, our new MicroClean does 4 fills on ProWash for a majority of loads and cleans and rinses circles around the Point Voyager at 4.0 gallons. Though the Normal cycle does well without a prewash and purge with single full deep rinse. Again, likely has a lot to do with design.

 

[michaelh]

I know we’re talking residential machines here but I wanted to make an additional point about commercial machines.

In the past, I’ve operated commercial dishwashers that use the last load rinse water as the wash water for the next load. Essentially and theoretically, it’s “clean” water. The wash water is drained and fresh hot water is brought in for rinsing. More recently, I’ve used and seen more machines, mainly conveyor machines, that reuse the same wash water continuously for every rack that goes through. If the main wash is ineffective because of dirty wash water or lack of pre rinsing, then your final rinse is pointless. That’s a disgusting thought to me, but understandably more economical, faster, and saves water. This is also assumed that the items are pre rinsed before they enter the machine.

Here’s how I view it. Regardless of home or commercial machines, washing is important, but rinsing is where you obtain the level of cleanliness or sanitation you’re looking for. So a pre-rinse/wash essentially is an important step, whether by hand or by machine, to give the main wash the best opportunity to clean the items.

You want each step of the cycle to progressively be cleaner than the last.

It seems to me over the years, pre rinsing has been a debatable issue depending on the type of machine you have or how powerful it is. When I was growing up, machines were getting more energy and resource efficient, and if you had a cheap, weak one arm machine, items were consistently coming out dirty. 50-60 years ago, some manuals said no prerinsing necessary, because the machine did it for you. Until home machines become consistent, this will always be debatable, because machines and results vary.

 

[michaelh]

Water turbidity sensing technology is where pre rinsing could be eliminated. But this isn’t across the board, yet.

 

[bpetersxx]

Maybe I'm not overwashing then

I just put it on heavy or pots and pans

But I have cruddy dishes that go into the DW

 

[gelaundry4ever]

cruddy dishes

I too put cruddy dishes in my dishwasher, and put it on smart wash HE. It does a great job.

 

[henene4]

Commercial DWs - tank or fresh water - have long been a seperate topic, just like a huge tunnel batch washer can be significantly more efficient per pound of laundry compared to a single load FL.

Many of these schemes use integrated "grey water" handling systems that can reuse rinse water as wash water, wash water for prerinses and so forth.

Actually, some DWs in some regions did exactly that. They had an extra port on the water diverter that would channel the final rinse water into a holding tank on one side of the machine.
The next cycle would then start by using that water.

Even further, there was a Fagor made H-axis TL that did the same thing with the final rinse water.
Wasn't long lived and nobody else did that for obvious reasons, but interesting nevertheless.

 

[Chetlaham]

I've noticed that to, latter Point Voyagers did partial purges and water top offs. My Maytag does the same sensing and for heavily soils. 

 

[lavamat_jon]

“ Whats interesting is it seems that sensors and cycle selection tend to vary the number of post main wash rinses more than they vary the number of pre-washes. I'm guessing they rely on these rinses for soil carry away once everything has been washed off the dishes.”

To be clear - the majority of auto cycles at least here mainly influence whether there is a pre wash or not. I’d say it’s 50:50 whether our Siemens will do a prewash or not on Auto, the Mieles I’ve used tend to be more geared towards doing a prewash than not on the auto cycle. Rinse wise, Mieles tend do only do one interim rinse whereas BSH have more of a tendency to vary the rinses.

Generally most European dishwashers have only really done one pre wash. The only ones I can think of that do more than one are on the G4000/G6000 series Miele dishwashers which did two prewashes on the Intensive cycle, although they only purge between the two prewashes rather than doing a full drain.

 

[Chetlaham]

Fascinating stuff. I've always been very interested in why one machine does one thing but another one does something else.

 

[DADoES]

 
One cycle on my DW doesn't have a prewash.  It runs wash (105°F), rinse, rinse (105°F), and no dry period.

The heaviest cycle is a prewash and two prerinses, main wash (150°F), three rinses (final 163°F).

 

[qsd-dan]

It runs wash (105°F), rinse, rinse (105°F)