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Dec 23, 2009 10:00 AM

Washing in "hot" water

I suspect that we put more faith in the germ-killing ability of hot water than we should. Is the maximum temperature we can tolerate on our skin while washing our hands or foodstuffs or dishes hot enough to disinfect? It seems far more likely that it's the water, soap, and friction that do the job.

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  1. You're absolutely right. Hot water that you can stick your hand in and pull it back with skin still on it, is too cold to kill germs, for the most part. That being said, the warm water plus soap help dissolve the grease and thereby flush them away. I have heard that the most effective way to (hand)wash dishes is to wash in warm soapy water but rinse in cool, and let air dry. I believe the thinking is that the cool water promotes the growth of whatever bacteria are left behind(and there definitely are some left behind)less than the warm water, and air drying introduces less than then a towel(no matter how clean you think that towel is).

    I for one, will continue to jam 2 day old crusted lasagna pans in the dishwasher, set it to "pots&pans" and go blissfully on my way, *knowing*:-) I am 100% protected(should this be in the "magic house" thread?lol)

    4 Replies
    1. re: nkeane

      Check your 5th sentence - I don't think you meant to write that cool water promotes bacterial growth.

      Edit: Oops - shaogo is right; never mind!

      1. re: greygarious

        I read that, too. Read the sentence again, though. at the end of a parenthesis there's the all-important "less" The essence: cool water promotes ... *less* than the warm water...

        On-topic: it's nuts to burn oneself. To disinfect hands, the water would turn hands bright red and burnt in no time. The combination of soap, warm water and washing time are the three factors that disinfect hands. That's easier said than done, however, or should I say done but with a price. I work in a restaurant. I must wash my hands at least once or twice an hour, going from handling money to food to cleaning etc. I don't normally have a dry skin problem, but my hands are bone-dry despite use of lotions (corn-huskers lotion is great, though) and the skin's starting to split in places. It hurts.

        1. re: shaogo

          try plain olive oil-- it's foodsafe ;-P i'm greased up constantly this time of year, but it's a trick to do it lightly enough that knives etc aren't slipping out of your hands.

          just a note that restaurant dishwashing systems (mechanical) go to temps of 180 and above (kills germs, bacteria, etc), and by-hand (3 sink system) have a separate sanitizing soak followed by air-drying, after the initial soap and rinse. it's a little weird to do dishes at home, they just don't seem clean to me w/out the sanitizing rinse.

          1. re: soupkitten

            Thanks, soupkitten! Indeed, I'll try the olive oil. It never occurred to me. There're many times I'll use my hands to spread olive oil on something, but that's just when I'm cooking for myself. I spend a lot of time working the bar at our place, and I fear that even if I have the tiniest bit of oil on my hands, I'll leave fingerprints on the glasses. Who knows, maybe I'll get used to using it a bit and washing off my fingers only.

            I'm also with you about the dishwasher. Our home dishwasher is extremely energy-efficient and I think that's why it takes longer than home dishwashers I'd become used to. Oh, what a luxury to have the restaurant dishwasher turn oily, greasy, caked-on saucy plates into squeaky-clean mirrors -- and in under a minute!

    2. I don't know if this is true or not, but a friend told me once that, from a foodservice safety perspective, the reason that warm (not necessarily hot) water is required for handwashing is because people won't tolerate the cold water for long enough to do a thorough hand washing.

      1. I grew up with the hot wash water in the sink, and a cool rinse in the other bowl. I have found that here in Hawaii a lot of people don't fill the sink at all, they keep the warm water running rinse first, then wipe/scrub with a soapy sponge and then rinse again. They dont think that having things soak in a warm batch of water gets things clean and is just a breeding place for germs.

        3 Replies
        1. re: KaimukiMan

          I don't know if this has anything to do with Hawaii. live about as far away from Hawaii as you can get and still be in the United States and this is how I wash dishes.

          1. re: KaimukiMan

            I think you might get arrested in CA for leaving the water running while you wash your dishes :) Or brush your teeth or shave. Naughty water wasters all.

            1. re: KaimukiMan

              i live in ct and this is how i wash dishes...

            2. Gloves - I wear them always when washing dishes and used pure hot water as it comes from the tap.

              22 Replies
              1. re: OCEllen

                The water coming out of your water heater should not be more than 140 degrees in order to avoid scalding (yes, it is a law.) That is not hot enough to kill anything.

                1. re: KaimukiMan

                  So if I crank my hot water heater up so the water coming out of it is higher than 140 degrees I'm breaking the law? Is it a criminal violation or just like a parking ticket? Will I have to do jail time? Will it be on my permanent record forever? What if the water heater is just set that hot but no one ever touches it?

                  1. re: taos

                    It might be one of those things.... The installer has to set it no higher than 140. After that I'd think it's a case of "well, it's your water heater". Though I suspect that were you to sell your house, you might be obligated to lower the temp.

                    *disclaimer: pulling this from memory, from a few little blurbs. So don't take my word for it :P

                    1. re: taos

                      Before this change (sometime in the 80's I beleive) hot water heaters were typicaly set to 160 or so, and resulted in many cases of people being scalded.

                      If you choose to set your's higher just hope no one visitng ever gets scalded, including any tradespeople, or you could have a nice fat lawsuit to deal with. I don't like the government interfering inside my home either, but most safety laws do have some basis in reality. I wouldn't advise you to take the railings off your staircase, or put plain glass in a sliding glass door instead of safety glass... but people do these things too.

                      1. re: KaimukiMan

                        Kamukiman is right IMO. It is really not good to set your water heater much higher than 120. At temperatures around 150 or so, there is a really big risk that eventually somebody will be scalded, perhaps badly, and if it happens to be, say, your 2 year old niece who was visiting you will feel really bad about that for the rest of your life, not to mention the effect on her. Don't take that risk.

                        If you hand wash your dishes in soapy 120-130 water, they won't be "sanitized", but the mechanical process of getting all the residue off is really good enough. Nobody is likely to get sick from them after that. If you insist on sanitizing, there are many home dishwashers that have sanitizing cycles (NSF rated) that will do the job--they have their own built-in heaters. That's probably your best bet.

                        1. re: johnb

                          Here's the rub. I don't have a dishwasher and I can't put one in. So I crank the hot water heater up as high as I can stand in an effort get the dishes clean. i'm not sure what the temp is. There's no thermometer on the heater, but it seems pretty hot.

                          1. re: taos

                            Since the temperature required to kill bacteria with heat alone would burn your hands, you are achieving nothing but a higher energy bill. Comfortably warm water is enough to soften congealed fat, which is then dissolved and removed by soap and elbow grease. Germs that aren't washed and rinsed away are killed by air-drying. Dishwashers were unheard of 50 years ago and most of the world still doesn't use them and nevertheless isn't succumbing to the germs on their teacups.

                            1. re: greygarious

                              What if I: 1) let the water run on the dishes without my hands on them? 2) wear gloves?

                              By the way, your statement that "dishwashers were not unheard of 50 years ago" is false. My parents had one in their suburban tract house that was built in 1956. I believe it came as standard equipment with the house.

                              Here's an article on the history of the dishwasher.

                              It confirms that the dishwasher was invented in the mid 19th century and installed mostly in commercial establishments until the home dishwasher became common place a century later.

                              I also worked as a commercial dishwasher at a large hotel in the 1980s. We used very hot water and wore thick rubber gloves so we wouldn't scald our hands.

                              In any case, the reason I use hot water, isn't because I'm hoping to totally santize the dishes. My dishes don't really need sanitizing. They're are too many free-flating germs around the house anyway. If I wanted sanitizing, I'd use bleach. I use hot water to get the grease off quickly and easily.

                              1. re: taos

                                I was a child in the 1950's on Long Island. Most of the houses in the neighborhood were built 10-20 years earlier, without them, and nobody had installed one. There was an occasional kitchen sink with an after-market disposal but even that was rare. So I'll amend that time frame to say that 50 years ago unless you had a newly built home, you were unlikely to have a dishwasher. Mine was built 40 years ago and has one that I never use.

                                1. re: taos

                                  Your last sentence is exactly why I do it. One of SIL's washes with tepid water. When they visit us, I wind up rewashing some things, esp. the wine glasses that can't go in the DW. (I dont let him SEE me do this.)

                              2. re: taos

                                You simply can't sanitize dishes by hand-washing them. As others have noted, the temps required would nearly immediately cause blistering burns on your hands.

                                If killing the germs on the dishes is that important to you, you can wash, rinse, and then sanitize them in a diluted bleach solution. Or pop 'em in a 175F oven for half an hour.

                                1. re: alanbarnes

                                  I don't know what you mean exactly by sanitize. It doesn't seem to be a major health risk to wash dishes by hand.

                                  1. re: Steve

                                    Sanitize - to make sanitary. To kill any microorganisms that may be present. Washing dishes with soap and warm water makes them clean, but it doesn't sanitize them. There is still the possibility that germs are present on the dish.

                                    Do I worry about this in my kitchen at home? Not a bit. But this thread is about killing germs.

                                    In commercial kitchens, health codes require that dishes not only be clean, but sanitary. This is typically accomplished either with heat (a commercial dishwasher gets up to about 180F) or with oxidizing agents.

                                    Ever notice the little 3-compartment sinks on food carts? They're required because one bowl holds the wash water, the second holds the rinse water, and the third holds a sanitizer.

                                    @johnb: I'm not saying that the dishes in a home kitchen need to be sanitized. I'm just saying that hot water isn't going to do the trick. And if somebody wants or needs to up the ante with regard to kitchen hygiene (for example, if somebody in the house is has a serious communicable disease or is immunocompromised), sanitizing dishes is one of many steps that should be taken, and it isn't an overwhelmingly difficult task.

                                  2. re: alanbarnes

                                    Of course it's also true that even if you do sanitize your dishes, by whatever method, there are so many other non-sanitary things around that are getting on your food (your hands for starters) that sanitizing them isn't going to accomplish anything anyway. It's akin to using a bulletproof vest to protect yourself from a gas attack.

                                      1. re: chef chicklet

                                        The microwave is an effective way to sanitize damp things - kitchen sponges, dishrags, etc. - but I'm not sure how it would work with dishes. The reason it's so effective with a damp sponge is that the water in the sponge gets the whole thing so hot that bacteria can't survive.

                                        But I don't know whether the microwaves could reliably overheat the moisture inside each individual bacterium. And if you're microwaving dry dishes, you're eventually going to roast your magnetron because there's not much if anything to absorb the waves. Never mind the potential problems with any metallic trim or paints...

                                        1. re: chef chicklet

                                          Use a 1:28 bleach to water solution if you're that particular. For that matter, you might as well add bleach to your tap water. Ever see what the inside of an old water main looks like? Lately my tap water tastes of bleach - this happens periodically, when the town supply gets compromised. Adding a little bleach to the drinking water in kennels and other animal housing is also safe, and standard in many operations.

                                            1. re: greygarious

                                              What are people doing in their homes that they need to chlorinate their dishes? It's a good suggestion for the paranoid or those with extreme immune deficiencies but for the rest of us this is overkill.

                                              1. re: KTinNYC

                                                I was responding to chef chicklet's quest for sterility - me, I fill the dishpan,
                                                add Palmolive detergent and hot tap water, let' em soak till the water is warm, then use a dishcloth, rinse under a thin stream of cold water, and into the dishrack to air-dry. The pre-wash in this house is 3 greyhounds and I am quite sure that on occasion I've mistaken dishes they "cleaned" for ones I've washed. Paranoid I'm not.

                                                1. re: greygarious

                                                  Yes, I know you were just answering a question. I certainly didn't think you were doing this on a regular basis in your home!

                                                  1. re: greygarious

                                                    LOL, gg. For years we never let my MIL know that the dogs (then Labs) were licking the plates. But now she loves the dogs more than us so it's okay :) And that way we're not wasting either - ah, how these threads weave, eh?

                              3. I am not aware of any warm water standard for killing bacteria. When I go camping, all the dishes get washed in cold water all the time. Same thing at primitive cabins. In fact, I would say that the cups and dishes at most primitive cabins never get washed in anything but cold water.