#60149 Dishwasher vs Handwashing

[Marduk]

YOU GUYS! HUGE NEWS!

So, I read a few questions on the board today (for the first time in, well, a long time) and noticed some missing information on a question. Against my better judgement, I posted a comment. AND YOU GUYS! IT GOT THROUGH! Gogo one for nine!

Here's the link, for posterity: Question 60149

[ahem.]

YAAAAY! Good work. (Also, I think most dishwasher do actually heat the water a little more than the water coming from the water heater... but it still only gets up to about 140 F.)

[Marduk]

That used to be true, but since the restriction on phosphates, the higher heats will destroy the enzymes that are now used prematurely, so they tend not to heat the water at all anymore.

Edited to remove the capitalization of phosphates. I don't know why I did such a silly thing.

[ahem.]

You may be right. I don't have my source material handy to argue one way or the other.

Krebscout, go get that book I gave you for your bridal shower and look this up. (Just kidding.) (Mostly.) (Um... not that I pre-read that before I gave it to you or anything.)

Edit: Nevermind, Krebsy, I did it myself. Here is some useful information from page 176-177 of Home Comforts: The Art and Science of Keeping House By Cheryl Mendelson

Sanitizing in the Dishwasher?

If you were running a food-serving establishment and wanted to sanitize dishes and utensils in the dishwasher, the 1999 Food Code would require that your machine first wash them with proper detergents or other cleaning chemicals, using a wash-water temperature of 150 to 165 F, depending upon the type of machine. Then it would require that the machine do a sanitizing hot-water rinse, either by immersion for thirty seconds in water 171 F or hotter, or mechanically, usually at a temperature of not less than 180F. By comparison, my dishwasher is designed to wash at 140 F and "sani-rinse" at 160 F.

Many of us would not be able to comply with these regulations at home because our machines don't get hot enough. Some dishwashers get only as hot at the tap water, which is usually around 140 F or even much lower in many homes. Self-heating dishwashers may or may not get hotter than that; how hot even they get may depend upon the temperature of the tap water they recieve. Few of us know how hot our machines are supposed to get, let alone whether they actually get that hot. Still, even if your dishwasher, like mine, does not heat its water as hot as 180F, it probably gets pretty hot, and once your dishes have been washed and dried inside it they are likely to be quite safe for use, given the potent combination of heat, strong detergent, and drying they have been subjected to. Moreover, hard, nonporous objects such as utensils and dishes, when freed of soil, subjected to a bath of strong detergent in good hot water, and thoroughly dried, are terribly uncongenial homes for bacteria. We do not really need to worry much about our dishes and utensils when they have been washed and dried in an ordinary, dishwasher.

[NerdGirl]

Oh yeah, I saw that comment and I thought it was awesome! I am not a fan of dishwashers because any dishwasher I've ever had left nasty bits of food all over everything because my roommates were too lazy to ever rinse anything before sticking it in there.

[ahem.]

Did anyone else see that NYT article that claimed pre-rinsing was dumb and wasteful? Ken Jennings recently blogged about it and expressed his doubt about thier claims in this post. This is the NYT quote:

(E)veryone I spoke to said prerinsing dishes before putting them in the dishwasher was not only unnecessary, it wasted thousands of gallons of water and could actually result in dirtier dishes.

“The soap needs something to work against to get the dishes clean,” said Lou Manganiello, who owns Household Appliance Service in Hawthorne, N.Y., and has been doing repairs for 23 years. For full disclosure, he has also ably repaired my appliances from time to time.

[thebigcheese]

That's the weirdest thing I've ever heard.

[Marduk]

Ugh, and now CPM is posting information contradicting mine. Can anyone (or CPM himself) tell me where he is getting this information? Everything I'm finding is repudiating it.

[ahem.]

I'm not sure what you're objecting to in his comment.

You indicated that most dishwashers don't get much above 120 F... and I'm pretty sure that's wrong. Quite a few DO have internal heaters. And even phosphate-free soap suggests washing at temperatures around 150 F. They wouldn't suggest that if the majority of dishwashers operate in the 120 F range.

Or do you disagree with the minimum sanitizing temperature he listed? You may have a point there. I wouldn't mind seeing a source for that stat. But keep in mind he's citing information about Residential Dishwashers, for which there is obviously a lower standard than industrial ones.

[thebigcheese]

Every dishwasher I've ever seen has an internal heater (and I've lived in 7 different apartments with dishwashers). The little metal bar that runs along the outside edge, right? I've burned myself on them before. And they seem to heat the dishes pretty well too. I usually can't stand to even touch my dishes when they're fresh.

And...for what it's worth...don't some dishwasher soaps contain bleach? That's enough germ-killing power to satisfy me.

[ahem.]

"Hot to the touch" is not really a good bench mark for whether your dishes are technically sanitized. I can barely put my hand under the faucet if I've turned it to full-on hot, and (as Marduk pointed out) tap water tops out at only ~120 F (depending on how high your water heater is set). So 120 F water will get your dishes pretty toasty, but that alone is not hot enough to KILL ALL THE GERMS. But clearly soap goes a long way in the chemical sanitation... otherwise handwashing properly would be completely impractical.

[Marduk]

Right, there's two points I was questioning, the first was the temperature and if it sanitizes; we would need to see durations as well as temperatures, and then know how many dishwashers actually meet those guidelines, and if they do so on cycles that are actually used (most dishwashers I've seen have a seperate "sanitizing" cycle that can be used, seperate from the wash cycle. But how many people would actually run their dishes twice to also sanitize them?) The second was whether this is actually preferable to the chemical component in most soaps, if the hand washing of the dishes will perform the job equally well.

[ahem.]

Here's a question I've always wondered about. Whenever I see instructions for washing stuff (hands, dishes, etc.), we're told to use soap AND hot water. I always kind of assumed the soap was the active cleaning agent, and the hot water was vaguely optional. It would obviously help dissolve the food/dirt/oil/whatever faster, get the soap off the object more thoroughly, and evaporate faster than room temperature water... but wouldn't my hands/dishes still be clean without the hot water?

I did about a million dishes during my last family reunion. Since we were camping in the middle of nowhere, the water I used was really pretty cold. Probably I was slowly poisoning my family?

[Craig Jessop]

We had a zone conference where the mission doctor over the whole Northeast area of the Church told us that the temperature of hand washing doesn't matter because it all turns into body temperature anyway. I don't know how seriously to take him, but that's what he said.

[C is for]

On a slightly related note, anyone else had trouble with the new phosphate-free dishwasher detergent? More and more of my extended family is quitting the dishwasher because the new soap won't get the dishes clean.

(We've been handwashing for the past year or two...ever since we got a new energy-efficient dishwasher in fact. But now more people are jumping on our bandwagon due to the soap.)

[ahem.]

Well, obviously hot water is better for the three reasons I mentioned. It is more efficient because it breaks down and dissolves gunk faster. It helps rinse the soap better, leaving less residue. And it evaporates faster, leaving a smaller window of time when the moisture can attract and nurture bacteria and such.

So it's better. I'm just not sure it's required.

And from what I've heard and read, tons of people are having issues with phosphate-free dishwasher detergent. Hopefully the industry will get on top of that and come up with something better.

[krebscout]

It's my understanding that soap itself is just a degreaser, and it's not antibacterial unless specifically stated. The hot water you use for your hands and hand-washed dishes is not hot enough to do anything, and it's more the friction of rubbing/running water that does the cleaning.

[Katya]

“The soap needs something to work against to get the dishes clean,” said Lou Manganiello, who owns Household Appliance Service in Hawthorne, N.Y., and has been doing repairs for 23 years. For full disclosure, he has also ably repaired my appliances from time to time.

Opposition in all things, perhaps?

[Marduk]

Ahem., you're exactly right. There's also another reason you don't have listed, and that is that soaps and sanitizing chemicals are designed to work at specific temperatures, so some of the elements will be more latent without water that is warm enough. But as krebscout pointed out, the water in and of itself isn't hot enough to do anything sanitization-wise, it is the agitation that does the cleaning, and the chemicals that do the sanitizing.

[Yarjka]

From Wikipedia:

Hot water that is comfortable for washing hands is not hot enough to kill bacteria. Bacteria grows much faster at body temperature (37 C). However, warm, soapy water is more effective than cold, soapy water at removing the natural oils on your hands which hold soils and bacteria.[5] Contrary to popular belief however, scientific studies have shown that using warm water has no effect on reducing the microbial load on hands.[6][7]

For handwashing dishes I usually use hot water since it gets food off easier, but for washing my hands, I actually prefer cold water, because I can tolerate it better than scalding hot water. That way I don't have to waste time trying to get the water temperature to just the right warmth - I just turn the cold on and get on with it.