[BJMarshall (OP)]

My wife seems to think that one must use hot water to wash dishes, and she disapproves of my using cold water. I am under the impression that it's the scrubbing action with soap and a washcloth that cleans the dishes rather than the temperature of the water. Does anyone know the science behind washing dishes by hand?

Regards,
BJ

[graham.d]

Generally speaking heat helps quite a bit. Nearly all chemical actions are more active at higher temperatures and so would aid the detergent action in removing unwanted substances. It also causes fats to soften and melt permitting greater penetration of the water/detergent mix. From personal experience it is definitely easier and much quicker to wash dishes in hot water.

I do note, however, that some washing powders (for washing clothes) are said to be designed for washing cold. Although this may be also a way of saving energy, the detergents may not be so eco-friendly and a main reason is because of the lower risk of leeching colours from fabrics.

[Geezer]

It doesn't really apply when you wash dishes by hand, but when you use a dish washing machine, the temperatures are high enough to sterilize the dishes. An even better aspect is that they don't get contaminated with a dish towel while drying.

[graham.d]

It doesn't really apply when you wash dishes by hand..

It does in my experience. In particular if you are cleaning baked on fat and carbon off a glass dish that has been in the oven. Your wife is obviously kind to you :-)

[Geezer]

Absolutely! Hot water is far more effective when washing dishes by hand, but I don't think the temperature will be high enough to do much sterilization, unless of course you have a pair of asbestos lined rubber gloves like the ones my wife got me to stop me complaining.

[JaneMiller]

I think hot water is better than cold water in dishwashing, especially when you clean the greasy dishes. However, cold water can be used to clean kitchenwares which you utilized to beat eggs. Do not directly wash those kitchenwares with hot water. Use cold water and wipe with a dishcloth or dish scrubber first. And then you can effectively remove off-flavor of eggs left in the kitchenware.

[alancalverd]

Anionic liquid hand dishwashing detergents are designed (yes, designed! I once did it for a chemical company!) for use in hand-hot water - around 35 to 45 deg C being optimum (any hotter can damage your hands). Automatic dishwashers run at higher temperatures and do a much better job with less water and a caustic (cationic) detergent that turns the fat into soap! Good point about eggs, however - worth a quick cool rinse before you put the mixing bowl in the dishwasher: tempera paint is colored eggwhite and lasts for thousands of years.

Enzyme ("biological") detergents for washing clothes work at lower temperatures - 30 - 40 deg C being preferred to activate the enzymes. Problem is that the reactions are slow and not really suited to dishwashing where the contact time is short. Non-bio fabric detergents are more effective at higher temperatures and therefore better for "allergy" or "overalls/linens/commercial" washes, way above comfortable skin contact.

You can get cold-water "camping" soaps and detergents that are useful on sailing boats where hot water can become a hazard, and some are designed for use with saltwater too, but the result would be disappointing on your best dinner service.

[Edwina Lee]

From a systems analysis point of view, defining the problem accurately is the first step of solving any problem optimally.
The problem needs to define 'washing dishes' and 'effectively' more precisely.
What has to be washed from the dishes, and what are 'dishes'?
And what metric(s) would effectiveness be defined?

[Bored chemist]

From a systems analysis point of view, defining the problem accurately is the first step of solving any problem optimally.
The problem needs to define 'washing dishes' and 'effectively' more precisely.
What has to be washed from the dishes, and what are 'dishes'?
And what metric(s) would effectiveness be defined?

Thanks for that.
Are systems analysts often invited to parties?

[alancalverd]

Of course! There are all sorts of parties to be analysed: pissups, birthdays, christenings, weddings, barmitzvahs….and once you have solved a reasonable spectrum, you can adapt the analysis to similar occasions. A true professional gets to work as soon as he receives the invitation, and responds with an opening questionnaire: objective of party? will there be music/dancing/beer/girls/food/car parking? stated objectives of other invitees (see previous list)? define previous list? metrics of success? How could you possibly do anything without a systems analyst?   

[VannyTr]

Hot water improves the washing-up effect and helps to wash away dirt and grease residues on the used dishes. And the latter, namely the grease, dissolves much more easily and quickly with hot water.

[charles1948]

Hot water improves the washing-up effect and helps to wash away dirt and grease residues on the used dishes. And the latter, namely the grease, dissolves much more easily and quickly with hot water.

You've summed it up concisely and perfectly !

[burgesssally787]

I think the fact is that at elevated temperatures all chemical reactions are a little more active. but I'm not sure if this applies to such temperatures. it usually takes really high temperature to intensify the reactions.
also now sell various dishwashing detergents that are supposedly effective in cold water, but as for me this is a marketing ploy.

[Bored chemist]

it usually takes really high temperature to intensify the reactions.

No, it doesn't.


However the biggest effect of using hot water is probably that it melts the fats.
It's easier to rinse away a liquid than a solid.

[charles1948]

it usually takes really high temperature to intensify the reactions.

No, it doesn't.

However the biggest effect of using hot water is probably that it melts the fats.
It's easier to rinse away a liquid than a solid.

Yes.  Hot water melts the fats and grease.  This is experienced by anyone who has to do the washing-up.

And it isn't a modern experience. It has been confirmed by past observers, such as George Orwell.

In his 1933 book, "Down and Out in Paris and London" Orwell recounts his experiences while working a thoroughly bad Parisian restaurant.  He says:

"There was no hot water laid on. Water for washing-up had to be heated in pans, and as there was no room for these on the stoves when meals were cooking, most of the plates had to be washed in cold water.  This meant scraping the grease off with bits of newspaper."


Doesn't this evidence from the past, buttress the concept that hot water is the essential ingredient in dish-washing?

[Bored chemist]

Doesn't this evidence from the past, buttress the concept that hot water is the essential ingredient in dish-washing?

No.
Because it says that hot water isn't essential.
It says you can use newspaper instead and then wash them in cold water..

Did you read what you wrote?

[charles1948]

Doesn't this evidence from the past, buttress the concept that hot water is the essential ingredient in dish-washing?

No.
Because it says that hot water isn't essential.
It says you can use newspaper instead and then wash them in cold water..

Did you read what you wrote?

Fair do's:

"How absolute the Knave is!  We must speak by the card, or equivocation will undo us" (Hamlet)

[Bored chemist]

We must speak by the card, or equivocation will undo us"

So, the Bard worked it out centuries ago,but you only just spotted it.

[charles1948]

We must speak by the card, or equivocation will undo us"

So, the Bard worked it out centuries ago,but you only just spotted it.

I spotted it years ago, BC, long before you googled the quote and identified it as Bard-derived.  Cued, no doubt, by my helpful "Hamlet" attribution.  Which I wouldn't have appended, except that I felt that without it, no-one on a modern Scientific forum would have a clue what it meant..

Shakespeare  had some insights into modern science.  His "Phoenix and the Turtle" threnody is worth perusing for concepts of modern wave/particle duality.

[Bored chemist]

long before you googled the quote and identified it as Bard-derived. 

There are a number of reasons why i didn't need to google it.
(1) the style- who else uses words like "knave"?
(2) my mother taught English.
(3) you cited Hamlet as the source.

Which I wouldn't have appended, except that I felt that without it, no-one on a modern Scientific forum would have a clue what it meant..

No, you have this the wrong way round.
Plenty of scientists read Shakespeare.

But there's a shortage of English graduates with even a a rudimentary understanding of physics or chemistry.

His "Phoenix and the Turtle" threnody is worth perusing for concepts of modern wave/particle duality.

No it isn't.
That illustrates my point.