Like most of us, I tend to think of my home as my safe space. But right now, our safety nets are threatened, and the fact that coronavirus is invisible to the naked eye adds a degree of stressful uncertainty to places that once felt secure. For the past few weeks, I’ve found myself amplifying my usual precautionary measures so I can keep myself, my family, my neighbors, and the people I might potentially come into contact with—directly or indirectly—safe.
Before I worked in kitchens, I worked in molecular biology labs. When I went to graduate school, I made up my mind to study infectious viruses and their genetics. I learned how to stay safe while working with infectious microorganisms, genes, and toxic and radioactive chemicals; along with that came the understanding that respecting the safety of others was of the utmost importance when working in a lab. (Not to mention that sloppy practices could alter experimental outcomes, leading to confusing and erroneous results.)
An early lesson that I picked up from one of my professors during a lab biosafety class was, “Assume everything and everyone is contaminated or a source of contamination." It's a rule that I’ve learned to live by, and I apply it not only to laboratory work, but also to my home and kitchen.
We've all read a lot about the risks and safety issues surrounding COVID-19, and Kenji did an excellent job reporting on the risk of coronavirus transmission through food. One of the main things to know is that scientists think that COVID-19 spreads primarily through close contact with infected individuals. While it's possible to become infected by touching a previously infected surface and then your face, the evidence indicates that's a less likely route of transmission. Still, this is a time when we should be observing the best hygienic practices out of an abundance of caution, both to avoid the spread of COVID-19 and also to prevent other illnesses from spreading—with hospitals under increased strain, we all want to stay healthy from any and all illnesses if we can.
But what does this all mean at the practical level of actually cleaning your home and kitchen? My goal here is to give you concrete instructions on how to clean a variety of household surfaces using the most commonly available cleaners and disinfectants. I’ve written this guide to help you with the basics of maintaining a clean and safe home, so that you can gain confidence and some degree of control during an uncertain time.
Sanitization Terminology to Know
Let’s begin by going through some of the terms that frequently come up and take a look at some of the most common and effective tools to keep your home space safe. The definitions below are based on what the terminology used by the CDC and informed by my own scientific studies and training.
- Clean: Clean refers to the absence of any visible particulate matter like chemicals, dust, fibers, etc. A clean object or surface will appear free of contamination to the naked eye, but can still contain harmful microbes and pathogens that can spread infection and even colorless chemicals that can go unnoticed. For example, rinsing a plate with water will remove food matter and give it a "clean" appearance, but that doesn’t mean it’s free from bacteria and other microbes; they might still be there and can transmit disease.
- Sterile: Sterility refers to the absence of any and all viable life that has the capability to reproduce and spread. Sterilization methods kill all bacteria, fungi and their spores, and viruses. Sterilization methods are indiscriminate: they wipe out both beneficial and harmful microbes. One thing to remember, though, is that just because an object or surface is sterile doesn’t necessarily mean it’s clean. For example, boiling water will kill living microorganisms and viruses, but that doesn’t necessarily mean the water is free from chemical and physical contaminants; the water needs to be filtered for it to be clean (filtration can also remove some bacteria and large microorganisms).
- Asepsis: Another term that you might encounter is asepsis, which is much more specific than “sterile" and refers to the absence of disease-producing bacteria, viruses, fungi, and other microorganisms. Physicians and biologists use aseptic techniques when they perform surgeries or run experiments to prevent introducing or spreading infections.
- Disinfection: Disinfection is a bit different from sterilization, though sometimes you’ll see the terms used interchangeably. Disinfection more specifically refers to the elimination of many or all disease-producing microorganisms except for bacterial and fungal spores. These spores can survive, and eventually grow and reproduce when they come into contact with favorable conditions, potentially causing disease.
- Antiseptic: A disinfectant is always used on inanimate objects like tables and kitchen counters. On the other hand, an antiseptic is a chemical that is usually applied topically on the surface of skin or on living tissue with the goal of inhibiting or destroying microorganisms.
- -cide/-cidal: Sometimes you will notice the suffix “-cide" or “-cidal" listed on the packaging of a disinfectant or sterilant; this refers to specific kinds of germ-killing activity. Some agents kill bacteria and are therefore bactericidal, others kill viruses and are virucidal. A germicide has both antiseptic and disinfectant properties.
We need to regularly both clean and sterilize our homes and the spaces we work in not only to keep us safe and reduce the risk of exposure from the COVID-19 but also from other harmful germs and substances that can make us sick.
Germs and Hot Spots 101
To defeat your enemy, you need to know who, what, and where it is. Knowing the make-up of microorganisms has helped scientists develop different ways to destroy them.
COVID-19 is a respiratory illness. Instead of DNA (deoxyribonucleic acid, the nucleic acid that carries our genes), this virus stores its genetic information in another type of nucleic acid, called RNA (ribonucleic acid). This RNA is protected by an envelope of proteins and lipids, and this envelope is covered in tiny protein spikes, which are what give this virus its crown shape—hence the name corona. It’s this spike that binds to the surface of our cells and leads to infection. Not all viruses contain envelopes, and therefore different methods of elimination are required depending on the virus type.
COVID-19 acts on our respiratory system and it primarily passes on from person to person when an infected person sneezes or coughs. When we sneeze or cough, we release tiny droplets of saliva and mucus into air that carry the virus with them, flying through the air until they land on nearby surfaces or people. Imagine a spray bottle containing water: When you press the lever, those droplets of water spread out in a mist over a large area. The virus in these droplets can survive on different surfaces for variable periods of time, so the safest route is to take a broad approach by assuming every surface might be contaminated. Our goal, then, is to clean, sanitize, and disinfect whenever possible to cut down the risk of transmission.
The type and nature of the surface matters in how we do this. Inanimate objects like kitchen counters and doorknobs need to be treated differently than our skin. Some surfaces like stone and wood can be porous, containing tiny cracks or holes that create room for microbes to seep in and hide, but also can absorb harmful chemicals, making it difficult to wash them off. Other materials like glass and metal can withstand harsh conditions in the form of heat and strong chemicals. Obviously we wouldn't want to do anything in an effort to sanitize them that could do harm to our bodies or render our food inedible.
Having a sense of the “hot spots" in your home is very helpful. These are areas with high traffic like doors, doorknobs, kitchen counters, tables, light switches, sinks, tables, chairs, TV remotes, elevator buttons, etc. Anything we at home touch with any frequency should be considered a source of infection and is best cleaned, sterilized, and disinfected.
By using a combination of techniques and methods, we can launch an attack from several angles, creating clean and sterile surfaces at home and in kitchens while maintaining a safe and healthy environment. The goal here is to reduce the number of microorganisms and viruses to as low as effectively possible, thereby reducing exposure and risk of falling ill.
How to Effectively Clean Your Kitchen and Home of Viruses, Bacteria, and Other Germs
First, make sure to wash your hands with soap and warm running water before and after cleaning, sterilizing, and disinfecting. Avoid scrubbing your hands aggressively and using very hot water because that can damage the skin and cause the skin to break, opening up new avenues for infection.
Next, it's time to do a thorough cleaning using one, or some combination, of the following chemicals and methods. A general thumb of rule when cleaning surfaces: first rinse and scrub with warm water and soap or detergent to remove any dirt and foreign materials. You can then apply a second disinfectant like alcohol, bleach, hydrogen peroxide, or other compatible disinfection agents that do not damage the surface being cleaned.
Not surprisingly, some of these agents have broader disinfecting capabilities than others, and in most cases the amount of time the agent is left on the surface, as well as how it is applied, will affect its degree of effectiveness.The American Chemistry Council Center for Biocide Chemistries has a more complete list of cleaners, disinfectants and sanitizers that are effective against COVID-19 and approved by the EPA.
Considerations when using disinfectants:
- Routinely disinfect surfaces, using your best judgement since you know which areas receive more traffic than others. In general, clean and disinfect high-traffic areas and surfaces daily, and low-traffic ones at least once or twice a week. Kitchen surfaces should be cleaned and disinfected daily, ideally both before and after use, while bathrooms should be disinfected at least once daily.
- Often it’s best to ventilate the room when disinfecting with agents like alcohol and bleach to get rid of any toxic fumes.
- Check expiration dates on any products you use.
- Read the manufacturer’s packaging label for specific instructions on appropriate dilutions recommended for maximum effectiveness and handling.
- Do not mix disinfectants together at home. Often these can react with one another, producing chemicals that are toxic and dangerous.
- Store disinfectants properly following the manufacturer's instructions. Improper storage can not only reduce shelf life, but also cause dangerous accidents.
- Test a small area first to see if the cleaning or disinfectant can damage the surface you are cleaning.
- Natural products like vinegar are not effective and not recommended for destroying viruses including COVID-19.
What personal protective equipment do I need?
- Always wear a pair of disposable gloves when cleaning and handling chemicals. If the gloves are reusable, make sure you limit their use to only cleaning and disinfecting. Check the manufacturer’s instructions to see if the gloves are reusable (some gloves can easily tear and, with repeated usage, fall apart). If you’re allergic to latex, nitrile gloves are an option. When wiping down surfaces, use disposable sponges or paper towels; if those are hard to find, reserve a sponge or cloth solely devoted to cleaning (i.e., don't use your dish sponge for this). Alcohol is better handled with non-latex gloves like nitrile, as alcohol can dissolve latex.
- If you’re using a spray, it's best to wear protective eyewear like goggles. Avoid inhaling the aerosols by using an appropriate respiratory mask, if you have one, and also ventilating the space well.
- To determine what to do if you’re exposed to a chemical accidentally while cleaning, check out the Material Safety Data Sheet (MSDS) for that chemical. Manufacturers are required to provide an MSDS for every product, and this information can be found online at their websites or through a quick search.
A Guide to Common Cleaning and Disinfectant Products and Methods
Like everyone else, you've probably tried to stock up on various cleaning products, but how well do you understand when to use which ones? Let's take a closer look at the most common cleaning and disinfecting agents and how best to use them.
Remember, though, there's no one right answer for what you should use to clean your home. You have a lot of options, so choose what to use based on what you have available in combination with the specific surfaces you're treating.
Water needs no real introduction. As a liquid, water is a very useful cleaning agent.
How water works: Water is the Universal Solvent—no other liquid comes close to its ability to dissolve and solubilize such a large and wide variety of substances. Substances that do not dissolve in water include metals, sand, some organic (carbon-based) substances like woods, fats, oils, turpentine, plastic, etc.
Where and how to use water:
- Rinsing with water helps remove and dislodge dirt and microbes. By itself, water is very useful against substances that dissolve in it, but not as useful against fats and oils. To remove fats and oils, soaps and detergents are most effective (see below), as is rinsing with warm or hot water: the high temperatures will help mobilize the fat and oil molecules and they will slide off much more easily. Wipe the surface dry using a dry cloth or towel.
- Many substances that dissolve in water will dissolve faster as the temperature of the water rises. For this reason, warm water is often much more effective than cold water at cleaning.
- Water is most often used in conjunction with other chemical agents like alcohol, detergents, and soap for maximum effect.
- Non-porous and porous glass, stainless steel, chrome, aluminum, stone, quartz, clay, etc. can all be cleaned with hot water. Make sure to wipe the surface dry after rinsing. Cast iron can be cleaned with hot water, but make sure it is dry to prevent any chance of rust.
- Do not use cold or very hot water when washing your skin; these extreme temperatures actually encourage people to spend less time washing up.
- Extremely hot water can also damage and hurt your skin during cleaning, causing burns and breaks in your skin that can promote infections. In some cases, extremely hot water can also damage heat-sensitive surfaces like glass, causing cracks.
- Never mix hot water with disinfectants like alcohol or bleach. These chemical agents are toxic when inhaled, and high temperatures increase the risk of breathing them in with steam.
- Do not leave puddles of water sitting on wood surfaces, finished or unfinished; it will eventually damage the wood.
Detergents and soaps
This is the first line of defense before you apply any disinfectants; if you do not have any disinfectants, soaps and detergents are still effective at eliminating many germs. Clean, scrub, and wipe down your surfaces with soap or detergent diluted in water.
What are detergents and soaps? In science terms, soaps (eg. sodium palmitate, sodium stearate) are potassium or sodium salts of very long fatty acids (the same fatty acids that are present in some of our fats and oils), while detergents (e.g. sodium lauryl sulfate) are potassium or sodium salts of long alkyl groups (a chain of hydrogen and carbon atoms joined together) with sulfur (called a sulfonate group). Soaps usually don’t foam as well and produce a scum in hard water; detergents don’t have this issue because of the sulfur group.
Soaps are derived from natural sources and are biodegradable, while detergents are synthetic and are typically not biodegradable. Detergents and soaps are like the lecithin in egg yolk that helps emulsify oil and water to make mayonnaise—they all contain a “head" that is attracted to water and a long “tail" that is attracted to fat, which makes them extremely effective tools as cleaners.
How soaps and detergents work: Detergents and soaps work by removing fats and oils from surfaces. They're able to do this so well because of that water-loving molecular head and fat-loving tail, which allows them to fully surround fat and oil molecules and carry them away in the water.
Detergents and soaps are also surfactants, which means they reduce the surface tension of water—the attractive force that holds water molecules together to form a drop. This is critical in cleaning because it allows water to spread out more fully (instead of gathering in droplets), which leads to more thorough wetting of fabrics and hard surfaces.
They can also help dissolve and disrupt the membranes of cells and viruses. In the case of the COVID-19 virus, the envelope is made up of lipids which are a family of molecules; when exposed to a detergents or soap, the lipid interacts with the fat-loving end of the detergent or soap molecule, which eventually disrupts and destroys the virus.
Where and how to use soaps and detergents:
- Detergents and soaps can be applied to a wide variety of surfaces. Soaps are usually applied on the skin while detergents are usually used to clean non-porous surfaces like plastic, glass, vinyl, glazed ceramics, tiles, and metal cookware and utensils, as well as clothes and fabrics. You can even clean surfaces with powdered and liquid laundry detergent by dissolving a tablespoon or two of the powder in 1 gallon of water or 1/4 cup of liquid detergent in 5 gallons of warm water. Detergents and soaps can also be applied to clean wooden surfaces like kitchen blocks and hardwood floors, but check the manufacturer’s instructions for guidance. Clay cooking pots and some porous non-glazed or non-sealed surfaces can attach substances like soaps and detergents and eventually release them into food, so detergents and soaps are not usually recommended for cleaning them. Instead scrub them with a little baking soda or salt and boil hot water in them to clean. Rinse with hot water to get rid of any traces of odors.
- When cleaning surfaces with soap or detergents, you don’t really need to soak them for extended periods of time unless a stain is stubborn (and the manufacturer recommends it). After applying the soap or detergent, rinse with water. Air dry or wipe dry with clean disposable paper towels or a clean towel or cloth.
- Often the manufacturer’s instructions will list recommended dilution amounts and application times (if applicable), so check the packaging for instructions.
- When washing hands, scrub your wet hands with soap well, then wash under warm running tap water (using warm water encourages people to spend more time washing their hands while extremely hot and cold water do not). Usually 20 seconds of cleaning is effective at significantly reducing bacterial and viral load.
Warnings: These days some brands of household soaps will be labeled as antibacterial because they contain chemical agents that kill bacteria. Whether or not some of these antibacterial ingredients used in hand and body washes are actually safe and useful is controversial. The FDA passed a ruling on this in 2016 citing them generally as not safe and effective due to the lack of data. Antibacterial agents are also ineffective against viruses.
What is alcohol? Like water, alcohol is a solvent, meaning it can dissolve a large number of substances and can also dissolve some organic (carbon-based) substances that won’t dissolve in water. There are three types of alcohol that are normally used as germicides: ethanol, isopropanol (isopropyl alcohol), and n-propanol (the latter is only used in Europe and not in the USA).
How alcohol works: Alcohol is effective as a disinfectant because it dehydrates and also destroys proteins by denaturing them. This can kill microbes and is effective against some viruses. The disinfectant capabilities of alcohol not only depend on the type of microbe and virus, but also on the length of exposure and also on the type and concentration of alcohol used.
Where and how to use alcohol:
- Alcohol can be used to disinfect skin as well as inanimate surfaces like metal, glass, and stone. Avoid using it on substances that can dissolve in it like rubber (See Warnings below for more details).
- According to the CDC, a 70% alcohol solution (made from 190- or 200-proof ethanol or isopropyl alcohol dissolved in water) is effective. You can also use rubbing alcohol (70% isopropanol) that is sold at pharmacies and grocery stores, but do not dilute it any further before using. Higher concentrations of alcohol are usually not recommended for a few reasons: 90% alcohol evaporates much faster than 70% alcohol, which means it has less time to do its job. In addition, 90% alcohol will coagulate the proteins on the surface of the cell and this forms a protective barrier outside the cell which can reduce effectiveness.(Do not use drinking alcohol like vodka to make disinfectants at home, since the alcoholic concentration of liquor is too low for it to be effective.)
- Store your alcohol solution in a glass or plastic spray bottle. To use, spray a surface with enough alcohol to cover and then wipe it down. Alcohol evaporates very quickly, does not kill bacterial spores, and can damage surfaces like rubber, so keep that in mind when using it. Alcohol-based disinfectants are sold as rinses, alcohol-impregnated wipes/pads, gels, and foams. Alcohol will be less effective on hands that are dirty and covered with debris, therefore washing your hands first with water and/or soap and then applying alcohol will be more useful.
- You do not need to wash or wipe down surfaces after disinfecting with alcohol. Alcohol is volatile and will evaporate very quickly.
- If using gloves, make sure you use non-latex gloves like nitrile when handling alcohol directly, as alcohol dissolves latex and will damage the gloves.
- Do not mix household bleach with alcohol: they will react and produce chloroform, a volatile and toxic chemical that should not be inhaled.
- Alcohol itself is highly flammable and volatile so keep it away from kitchen stoves, warm spots, and direct sunlight. As the temperature rises, alcohol evaporates and a bottle exposed to heat can explode.
- Surfaces like rubber, vinyl, or metal surfaces that are coated with a protective layer of oil or fat can get damaged with alcohol (read: don't use it on your cast iron). Alcohol can dissolve rubber and also strip off the layer of oil or fat on cast-iron surfaces causing eventual damage. Do not use alcohol on finished wood surfaces, it will strip the varnish and polish and destroy them.
What is bleach? Bleach is one of the most powerful chemicals and one of the most frequently used agents in labs, hospitals, and at home because it kills almost 99% of known microorganisms and viruses. It is usually sold commercially as a liquid or as crystals (the active ingredient in each of these is different). The bleach in this section refers to chlorine-based bleach; note that hydrogen peroxide is also a bleach, but is a non-chlorine based bleach.
How bleach works:
- Sodium hypochlorite is the active ingredient in liquid bleach. It releases a particular type of chlorine in water and it also has a highly alkaline pH, both of which change the chemistry and structure of proteins in cells and viruses upon contact, killing off the bugs. In the case of the COVID-19 virus, bleach first works on the outer glycoprotein coat, destroying it and killing the virus.
- Unlike liquid bleach, bleach crystals contain a different active ingredient called sodium dichloroisocyanurate and it can disinfect surfaces, medical equipment, and sometimes water.
Where and how to use bleach:
- To use liquid bleach, dilute 5 tablespoons (74ml) unexpired liquid bleach in 1 gallon (3.8L) water, or 4 teaspoons in 1 quart (950ml) water. It is best to dilute liquid bleach cold tap water, because warmer temperatures will release more toxic fumes. Make small diluted volumes of bleach as they are best used within 24 hours and lose their effectiveness as a disinfectant (it will still work as a bleach for fabrics). Store diluted bleach in a plastic bottle or a spray bottle; if using a spray bottle, make sure the spring mechanism is not made from metal, as bleach eventually corrodes metals and the spring will spoil.
- Wipe your diluted bleach solution on a surface like glass, glazed ceramics, stainless steel, flatware, plates, tools, floors, etc. and then let it air dry. Alternatively, you can also wipe or rinse the surface with clean water after use. Make sure the room you are using bleach in is well aerated because the fumes are toxic if inhaled.
- Clorox Control Bleach Crystals can be dissolved in water and used to disinfect hard non-porous surfaces like sinks, glass, floors, etc. Check the manufacturer’s instructions before using bleach crystals as a disinfectant. Based on what I’ve found and read, there are some concerns regarding its safety due to the limited data available on exposure.
- Bleach can decolorize laminate countertops, so avoid use. If you must, apply quickly, clean with water right away, and air dry.
- Porous surfaces like fabrics, curtains, and rugs that can be washed should be laundered with bleach (in hot water if possible) based on the manufacturer’s instructions.
- Bleach is highly reactive. Do not store it in metal containers and keep it away from heat and light.
- Avoid mixing bleach with ammonia-based cleaners because they will react and release toxic fumes. Bleach will permanently decolorize fabrics, it can corrode metal surfaces, and even destroy some stone surfaces like marble. Bleach can be applied on stainless steel surfaces, but wipe it down immediately after using to prevent any risk of corrosion; rinse and wipe well with clean water after use.
- Do not mix bleach with hot water when making dilutions for use at home. Use cool tap water or water at room temperature.
- Bleach is highly volatile: do not expose it to heat and always use it in a well ventilated room before applying. The vapors are toxic.
- Bleach is usually not recommended for porous surfaces like wood (it can be used on exterior finished wood surfaces but not interior hardwood floors and furniture). It is best to test wood before attempting this as bleach will and can destroy the finish. Bleach, however, can be used to disinfect kitchen wood blocks and counters that are free from any polish, colors, or finishing chemicals. When applying, scrub in small amounts to prevent the wood from absorbing the bleach and rinse with warm water immediately.
What is hydrogen peroxide? Hydrogen peroxide is a liquid and is used as a disinfectant on inanimate objects and surfaces. Hydrogen peroxide is an example of a non-chlorine based bleach. When the detergent OxiCleanTM is mixed with water, a chemical reaction occurs that produces hydrogen peroxide, which helps to remove stains.
How hydrogen peroxide works: Hydrogen peroxide is an unstable chemical and degrades in water to produce a special type of oxygen called nascent oxygen—an atomic form of oxygen that is highly reactive. Nascent oxygen attacks lipids, proteins, and nucleic acids and thereby acts as a disinfectant that kills bacteria, viruses, fungi, and spores.
How to use hydrogen peroxide:
- A 3% solution of hydrogen peroxide destroys rhinovirus, the same virus that is responsible for the common cold, within 6 to 8 minutes of exposure and is likely effective on the COVID-19 virus as well.
- Use gloves when handling hydrogen peroxide.
- Hydrogen peroxide can be applied to a wide variety of porous and non-porous surfaces. It can be used on wood, however it can also pull out any stains if they were applied to some wood surfaces like hardwood floors, furniture, and some kitchen chopping blocks, so test the surface in a small spot before you apply.
- Hydrogen peroxide does not last for more than 30 to 45 days once opened. An unopened bottle of hydrogen peroxide usually has a shelf life of about a year. Check the manufacturer’s instructions.
- One way to check if your hydrogen peroxide is still active is to look for effervescence (tiny bubbles): If you apply a few drops on your kitchen sink, it should bubble which means that the product is still useful. A second way to test the quality of hydrogen peroxide is to use yeast. Some bacteria and yeasts like baker’s yeast produce an enzyme called catalase that accelerates the production of oxygen from hydrogen peroxide. If you add a few drops of a growing yeast culture (any type of baker’s yeast, such as instant yeast or active dry yeast that's been revived in warm water) that is awake and growing will produce the enzyme, you will see a lot of bubbles quickly if the hydrogen peroxide is still unexpired.
So far I have discussed chemical methods of cleaning and disinfecting, but there are physical methods (i.e., non-chemical) methods that are used at homes and in labs and medical settings to kill microbes and viruses. Chief among them is high heat.
High temperatures are best applied to certain foods and inanimate objects that will not be damaged by heat. Cooking food in many cases not only serves to produce flavor and improve texture, but it also kills microorganisms and viruses. Heat causes stress in cells, denatures proteins rendering them useless, and alters cellular membranes which ultimately lead to death. Heat can be applied to kitchen equipment and even fabrics, but it is much harder to apply heat to kitchen counters and other surfaces, making it less practical for them.
Heat can be used in two different ways: dry and wet. For all these methods, the material being disinfected by this method must be heat-resistant, lest it break or melt when exposed to high temperatures.
Dry-heat sterilization: As the name suggests, dry heat involves no water and only the application of high temperatures to sterilize.
How to sterilize with dry heat:
- Heat-safe kitchen tools and equipment must first be washed with soap and cleaned with water and then dried.
- In labs, the equipment is usually placed in special heat-proof bags and then heated in a forced-air oven sterilizer. The FDA recommends 340°F (171°C) for 60 minutes or 320°F (160°C) for 2 hours to effectively sterilize equipment. These conditions ensure the destruction of microbes, viruses, and even spores. You can do a version of this in your oven at home: first preheat your oven to either of the temperatures. Wash and completely air dry your kitchen tools (they should be heat-safe) by placing them on a clean kitchen or disposable paper towel, and then place them in a clean heat-proof dish or tray. You can cover the dish with one or two layers of aluminum foil. Place the dish in the oven and heat for the appropriate time based on the temperature listed above. Avoid overcrowding the dish or tray. Once done, let them cool in the oven for 30 to 45 minutes and then bring them out.
- Canning tools and jars can be sterilized by this method.
- Not all materials can withstand the high temperatures used.
- While the use of heat-proof bags is not always practical or possible in homes, you can use dry heat to sterilize your kitchenware.
Moist-heat sterilization: In our kitchens, the dishwasher usually achieves this by applying a combination of water, some type of detergent and/or soap, and heat to clean, disinfect, and dry our cookware and utensils. But there are other ways to use hot water to sterilize utensils and fabrics as needed.
This method involves a combination of high temperatures and the high pressure created by water as it is converted to steam. Boiling and autoclaving are two methods that fall into this category. Autoclaving is used in labs and in medical facilities to ensure sterility and is much more effective than dry sterilization.
How moist-heat sterilization works: High heat causes cell death by destroying proteins and kills microbes and viruses and spores. Steam is also much more potent than just hot dry air at penetrating cell walls, which makes moist-heat sterilization a much more effective method than dry-heat sterilization.
How to sterilize with moist heat:
- You can immerse kitchen tools, jars, bottles, etc. in a large enough pot with enough water to completely submerge them. Make sure there are no air bubbles trapped anywhere. Bring the water to a rolling boil and then continue to boil for 5 minutes. Let the water cool and carefully remove the materials being sterilized. Place them on a clean mat or towel to dry before using.
- While autoclaving at home is not possible for the most part , you can rig a pressure cooker to sterilize tools that can fit. In fact, these scientists tested the use of electric pressure cookers, including the Instant Pot, to see if they can kill bacteria and be used in labs. It worked.
- Just like dry heat, moist heat cannot be applied to heat-sensitive kitchen materials.
- If water remains on the surface after sterilization, it can corrode and rust some metals.
- Repeated sterilization by this method can cause extensive wear and tear over time, even on metal and glass.
Ultraviolet (UV) light
What is UV light? Besides using bleach and alcohol in the labs, UV light is another way to ensure sterility. While there are a few devices that are now available to sterilize your cell phones, in general using UV light to disinfect your home is a bit trickier and can be hazardous. My discussion here is limited to the mechanistics to give you a sense as to why it is not a practical tool to use at home.
How UV light works: UV light works by crosslinking molecules like proteins and DNA inside cells and viruses. This causes extensive damage and even leads to mutations which kill microbes and viruses. However, U.V. light works at surface level best because it has a low power of penetration, and it's dangerous if used improperly: exposing your skin directly to UV will cause burns (the same reason as sunburns) and even cancer because it produces DNA mutations.
Here are some additional links with further information to help you stay safe.
- WHO – Myth Busters on COVID-19
- CDC – Clean and Disinfect Recommendations for US Households
- This is a handy online calculator to determine dilutions when making disinfecting solutions at home.
- A list of cleaners, disinfectants, and sanitizers.