What are the benefits and drawbacks of washing dishes in hot water


When hand-washing dishes, it seems commonplace to wash dishes in hot water.

This LifeHacker article about washing your hands in hot water versus cold water points out that:

It's certainly true that heat kills bacteria, but if you were going to use hot water to kill them it would have to be way too hot for you to tolerate

But sometimes when hand washing dishes the water can be uncomfortably hot (i.e. you wouldn't put bare skin under it for extended periods of time and consider that gloves are sometimes worn) — hotter than what would be discussed in the article.

Also consider this Housekeeping About.com article in which it asserts claims about using hot water:

  1. Cleaning Power

    • Hot water actually helps to lift away and clean dirty dishes
  2. Killing Bacteria and Microorganisms

    • Hot water is needed to effectively kill bacteria on dishes
  3. Cutting grease

    • Water temperatures under about 90 degrees will leave a nasty greasy film on your dishes

    • Grease cutting ability is severely hampered by cool water

  4. Drying Time

    • Hot water dries much more quickly on dishes than warm or cool water

And also:

Dishes will dry spot and streak free with hotter water

However, these all seem to be claims that can be easily assumed. Since most people use warm-to-hot water they would assume it is the reason the dishes are spot free or rinse off easy. Reading the article leaves me asking "why?", how?" and "but wait I just saw a source saying the water isn't hot enough to kill bacteria and microorganisms?".

There are no sources for the information either, and the fact it is About.com leaves me skeptical.

What, if any, benefits are there of hand washing dishes in hot water? What about drawbacks?

Best Answer

Before we proceed, we should note that not all dirty dishes are created equal. There are a few "groups" with different chemical and physical properties.

  • Sugar
    Probably the easiest of all as it will happily dissolve in water. A bit quicker in warm or hot water than in cold water (iced tea, anyone?), but not adverse to being washed off. We can probably ignore it for our further discussion.
  • Starch, uncooked
    Pure starch will easily dissolve in cold water, but tends to form lumps in hot water as anyone trying to thicken a soup or sauce can attest. This means all starchy dishes, from your bread bowl to the spoon in your bag of flour needs to be rinsed cold (first) or you will end up with a glue-like substance clinging to your dishes, your rag, your brush, whatever. You need to create a suspension, that is tiny particles floating in your water instead of a sticky goo.
  • Proteins, unheated
    Unheated, that means uncoagulated proteins, like the yolks in your breakfast egg or that cup with fat-free milk, even the cutting board of your meat are comparatively easy to dissolve in cool-to-lukewarm water - everything below their specific temperature at which they denaturize. This does not mean that they are clean after that because there are:
  • Fats
    This is the one group that really, really needs some solvent, aka dishwashing liquid for simple chemical reasons: Fats are hydrophobic, they do not mix with water. Your soap binds with the fat molecules forming larger molecules, that are then soluble in water. Hotter water speeds up this process, similar to sugar dissolving faster in hot water. Plus food fats that are solid at room temperature turn liquid when warmed which helps the soap to "get" the fat molecules. No need to boil your hands, though.

Now unless you serve a very restricted breakfast, your dishes will likely contain something of each group above, so you need an adjusted approach:

Those dishes that have starchy and protein-rich components may benefit from a cool rinse first. Then your dishes can go in the sink with quite warm water - hotter speeds up the "loosening" of fats and other crusts, but you need not "boil" your hands, gloved or not.

Yet we still have to consider our nasty hitchhikers:

  • Bacteria and their ilk
    Let's get one misconception out of the way first: Washing dishes, whether by hand or in a dishwasher, does not remove all bacteria. You can scrub and sanitize to your heart's content, your kitchen will never be truly sterile. And it doesn't have to. The human body deals well with some "intruders" on average, they can even be beneficial.
    What we want to do is to reduce the total amount of bacteria present and, if possible, eliminate those that are highly pathogenic. (Don't lick that raw chicken...!) Unfortunately, the suggestion of washing your dishes with really hot water to kill them is impractical at best - Salmonella dies at about 70C / 155 F1, similar rules apply for Listeria.
    Bacteria doesn't come alone, it is on and in the food. So cleaning the dishes well and removing all residue will in fact rinse the bacteria right off and leave the very few that still might cling to a plate without food, causing many of them to die. Much more critical is the great bacterial breeding ground near your sink: Sponges and rags may contain far more pathogens than a random plate - your food is typically not contaminated to the hilt from the start. So make sure you rinse your dishes well after washing, consider air-drying or at least use a fresh towel.

1 To be precise, it's a function over time and temperature, but that doesn't make much of a difference here.