When must a Knife be Cleaned and Sanitized?

When to clean a knife? Every time you handle different food ingredients.

When to sanitize a knife? After cleaning the knife.

That’s the short, simplistic answer. In the reality, there are some nuances to it.

As a Registered Dietitian, I spent years in the college not just studying nutritional elements academically. My colleagues and I learned to “properly” cook in the kitchen too so we’d get a deeper understanding of nutritional science (at least, that’s what they do in my uni).

As we all know, cooking is the fun part.

The unfun parts are the scrapping, washing, drying, and storing the utensils. Furthermore, things like accidentally cutting your hands accidentally or needing to an old, kept-in-the-drawer knife certainly call for a special treatment.

In this article, I’ll share a few things I’ve learned about taking care of our knives from my knowledge and experience as a health professional.

WHY Should You Clean a Knife Regularly?

A few months ago, a certain supermarket retailer got tangled in a salmonella outbreak, supposedly from the meat they sold.

Despite the bad press, it seems the store wouldn’t get dragged down since they’ve employed the proper safety handling and proper cooking for the meat.

Now, could you imagine what lawsuits would ensue if only they got caught not cleaning their knives properly?

Okay, that’s a bit stretching. But my point is clean knives are important, and here are several reasons you need to pay more attention to it:

1. The Risk of Food Poisoning

Certain types of food contain dangerous bacteria and viruses. If consumed, these pathogens can cause an illness. E. coli and salmonella are often found in raw meat (chicken, beef, fish).

On the other hand, vegetables may also cause disease due to the use of pesticides in the planting process.

Knives that are not cleaned after being used to cut raw meat or even vegetables and fruit can cause bacteria and chemicals to spread throughout the kitchen (sinks, cabinets, stoves, dining tables, and other equipment).

2. The Risk of Cross-Contamination

Cross-contamination is the transfer of harmful bacteria from one food to another food or equipment.¹

For example, you just cut a piece of salmonella-ridden meat. Without cleaning the knife, you cut the vegetables, cheese, bread, and every other organic matter that exists in your kitchen. Congratulations, you’ve just cross-contaminated the entire kitchen!

Cross-contamination can cause poisoning as a result of using the same knife to handle different types of food. A knife used to cut raw meat shouldn’t be used to cut vegetables without first washing and cleaning it.

3. Handling Allergenic Ingredients

Some people are allergic to certain food ingredients. I know it’s shocking, but they cannot eat certain types of food. Thus, they have to look for another food type as a substitute.

For example, you will cook a seafood stir-fry dinner, but a family member is allergic to shrimp. There should be an alternative dish, like chicken. So, the knife used for cutting shrimp must be washed first before cutting chicken, even though both are still fresh.

4. Ensuring Taste Quality

Truth be told, there are some situations where it’s okay to use only one knife — for example, cutting fruits and vegetables or cutting bread and pastries. Technically, it’s not a health hazard, but the remaining food or liquid will undoubtedly cause a mixed flavor. If I dare to surmise, not everyone would like that.

For example, a knife used to cut kiwi fruit is used to cut cucumber. Not everyone will like the mixture of the sweet and sour taste of kiwi and the fresh taste of a cucumber.

5. Keeping the Knife Looks Good and Lasts Longer

Cleaning your knife will keep it looking visually appealing. Its sparkling blade and clean handle make the cooking process more enjoyable.

Unless cleaned regularly, sometimes leftover food residue can cause iron deposits in the knife. You know this phenomenon better as rust. The quality of your knife will only be maintained if it is cleaned regularly.

WHEN Should You Clean a Knife?

When must a knife be cleaned and sanitized? This cutting tool should be cleaned every time you handle different food ingredients. This is especially true when you are handling both raw and cooked ingredients.

Prep some spices, then you want to slice the meat? Clean the knife.

Sliced some meat, then you need to cut the vegetable? Clean the knife.

Cut the vegetable, then you remember to scale the fish? Clean the knife.

In an ideal world, cleaning the knives is a part of the after-cooking ritual in your kitchen.

Here are the more detailed conditions on when you should clean your knife:

1. You are Using an Unwashed, Brand-New Knife

A newly purchased knife does look clean, mainly because it is usually stored in a package. Yet, the possibility that someone else has touched the knife still exists.

We can’t determine whether the hands of the people doing the packaging process are clean. There is a potential for bacteria and germs to transfer from their hands to the new knife. The packaging isn’t necessarily that “clean,” either. Therefore, before using a new knife, always clean it thoroughly first.

2. You are Using the Same Knife for Different Food Ingredients

Raw meat is a source of germs and bacteria that can spread throughout the kitchen. When you don’t clean the knife you use to cut the meat before handling other food ingredients, it will spread without realizing it.

If you only have one knife at home, the knife used to cut fish must be washed and cleaned first before using it to cut vegetables and fruit. Remember that you have to wash the cutting board too. It’s useless if the knife is clean, but the cutting board isn’t.

3. Several People Use the Same Knife

Imagine a mother and child are cooking dinner together. The mother is cooking the animal protein, while the child is in charge of cutting the fruit. They only had one kitchen knife.

Even though these two preparations occur at the same time, the knife must still be cleaned when its user changes from mother to child (or vice versa).

Cleaning a knife is not only limited to the blade but the handle, too. A person’s hands may touch other contaminated surfaces (even if they appear clean), thereby spreading it through the knife handle.

4. After Every Use

Even if it is only used to cut fruit, which may seem clean and safe, you should still clean your knife before storing it again.

When throwing leftover food into the trash, don’t forget to keep the knife away from the waste or other potential sources of contamination. It is better to use your hands to remove the waste rather than a knife.

5. After You Accidentally Cut Yourself

It has been scientifically confirmed that knives stained with the user’s blood can contaminate other foods if you use them without any sterilization process. Don’t forget to disinfect the cutting board or other utensils as well if the blood touch them.

6. After Sharpening the Knife

Sharpening will cause the metal at the very edge of the blade to break into tiny pieces.

If sharpened knives are not cleaned before use, metal pieces will likely get into your food. The consequences range from food taste changes to heavy metal poisoning.

HOW Should You Clean a Knife?

Here is a good step-by-step process to clean your knife:

1. Before starting the cleaning process, remove all food residue stuck to the blade (e.g., bread crumbs, cheese, pieces of fat, etc.) using a paper towel.
2. Make sure the blade is facing away from you. Always avoid cleaning the knife with its blade facing you.
3. Run it under running hot water or soak it for some time.
4. Apply dish soap to both sides of the blade along with the handle and let it sit for 20 seconds. 
5. Scrub the blade and handle with a clean sponge. Don’t rub too hard. Position the sharpest part of the knife facing away from you.
6. Rinse the blade under running water. Make sure there are no food fragments left.
7. Dry the clean knife with a paper towel or towel immediately after rinsing the knife. If not dried immediately, rust can easily form on the blade if the knife is allowed to air dry.

For better cleaning, you can use a brush/scrub with hard bristles (dish brush). Its bristle will help you scrub and remove stuck dirt.

I know some of you use stainless steel scrub pads to remove the stubborn stuffs (they’re annoying, after all). However, try to avoid using it as it could damage the blade’s surface. Stay away from bleach, vinegar, salt, or other harsh cleaners, as they can cause rust. Minimize washing the knife using a dishwasher too for the same reason.

WHY Should You Sanitize a Knife Regularly?

Apart from cleaning knives, why do you need to sanitize knives?

The cleaning process will remove dirt and contaminants visible to the naked eye. However, bacteria and viruses are still very likely to be in the knife area. Therefore, sanitation is needed.

The sanitizing process is carried out to eliminate invisible bacteria and viruses and ensure food safety.

Cleaning and sanitizing have different purposes, yet both are crucial. Even though it looks promising, sanitizing should not be used as a substitute for cleaning.

What’s the DIFFERENCE between Cleaning and Sanitizing a Knife?

	CLEANING	SANITIZING
Purpose	To remove most food particles, dirt, and other objects from the surface of objects	To reduce the number of germs on objects and surfaces to levels that are considered safe.
Process	Rubbing with soap, washing, then rinsing.	Usually using chemical solutions, or heat, or UV light.
When	Before sanitizing the knife.	After cleaning the knife with soap.

Table of the differences between cleaning and sanitizing.

WHEN Should You Sanitize a Knife?

Cleaning is the initial stage before sanitizing. Sanitizing can only be done after the object has been cleaned.²

The sanitizing process is emphasized more if:

• The same knife is used to process or handle food for people with certain allergies (for example, seafood allergies),
• After handling food ingredients that have a high potential for contaminating other foods (for example, raw meat, raw eggs, or dough),
• The knives have been stored for a long time but are about to be used again.

What are the Available METHODS for Sanitization?

METHODS	PROCESS
Heat Sanitization	Using a dishwasher set to high temperature or soaking the knife in boiling water for at least one minute.
Chemical Sanitization	Using a sanitizing solution, for example 70% rubbing alcohol.
UV-C Sterilization	Using a tool that emits UV-C light and is exposed to all parts of the knife.

Table of the common sanitizing methods available.

HOW to do Simple Sanitization at Home?

Even though sanitization is most effective when done using certain equipment or chemicals, you can do it yourself at home. You just need some boiling water to do it.

Here’s the step-by-step sanitizing process you can do at home:

1. Prepare a pan or cooking pot that is large enough to fit your knife into.
2. Turn the heat to as low as possible.
3. Put your knife in the pan and soak it with water.
4. Cover the pan and let the water boil for a few minutes.
5. Carefully remove the knife from the pan, let it cool for a few minutes, dry it, then store it.

USDA pointed out you’d need to sterilize the cutting board and utensils that touch the food directly. For the countertop and other kitchen surfaces that don’t directly touch your foods, you can disinfect them using a DIY disinfectant. Just mix a solution of five tablespoons (one-third cup) of unscented liquid chlorine bleach with one gallon of water.¹

HOW to Store Your Knife After Cleaning & Sterilizing?

Okay, in this last part of the article, I’ll give some pointers for storing your knife based on nutritional science. Here are a few of the most important tips to remember:

1. Store Your Knife in Clean and Dry Condition

Store your cooking utensils, especially the knives, clean and dry. “Clean” means they have been washed with soap. “Dry” refers to after removing the water, preferably using a towel or paper towel.

Avoid allowing the knives to dry on their own, as this can cause rust to appear (iron deposits).

2. Dispose the Rusted Knives Properly

Cases of tetanus have been linked to the entry of rust into the body, especially when exposed continuously in increasing amounts. However, using rusty kitchen utensils rarely causes tetanus because few of them exist.

On the other hand, using a rusty knife has a more direct impact on the taste of the food. Rust is a form of oxidation of iron, so it will contaminate the taste of food (just imagine the iron tinge of your blood if you accidentally taste it).

Furthermore, the USDA has previously stated that rust is not safe to consume, so it should not be ingested.¹

If your kitchen equipment has rusted, more so if the iron deposits have fallen off, replacing it with a new one would be better.

A knife is dangerous, so don’t just throw it in your trash bin to dispose of it. At the very least, you should wrap the blade securely using multiple layers of tape or cardboard. The key is to prevent accidental cuts and minimize the risk of injuries that could happen from it.

Contact the local waste management, recycling centre, or scrap yard near you to check more about disposing of your knives.

3. Recommended Types of Storage for Knives

There are some equipments I can recommend to help you better store your knife:

• Magnetic Knife Rack. Placing knives on wall-attached magnets can be an efficient and modern option to store your knife. It is located within eye distance, easy to retrieve, and saves your kitchen space. The magnetic strip is also easy to clean. However, you must hang it on a sturdy basic material to avoid falling easily.
• Knife Sheaths. A knife sheath can be used to protect the blade. Storage becomes more manageable, especially in a drawer or cupboard, without damaging the sharp parts. Knife sheaths are also usually easy to clean.
• Knife Rolls. Storing knives in a roll is frequently done by chefs and people who travel a lot. The cleanliness and sharpness of the blade can be maintained easily.

4. Avoid These Types of Storage for Knives

On the contrary to what people usually use or see from the media, you should avoid using these tools/methods to store your knife:

• Knife Block. Storing knives on a knife block looks efficient because they can be placed close to the kitchen counter, making them easier to insert and remove. In real life, though, it is difficult to clean the slot because the space is small. Dirt builds up and damages the blade. Knife blocks are also usually sold as a set with the knife, so other knives (from different brands) may not fit there. So I’m not fond of this piece.
• Kitchen Drawer. Storing knives in a drawer is usually the safest way to keep them away from children and pets, doubly so if you can lock the drawer. However, storing knives this way can’t be done carelessly. It’s just plain dangerous to place a sharp blade together with other utensils. It can also dull the knife. If you want to store your knife inside the drawer, you’d better use drawer inserts/trays. It’d help  to make the drawer safer as well as to avoid damaging the blade. The biggest drawback of drawer trays is that it is hard to clean them thoroughly. So, it’s can be unhealthy for something so close to your cooking tool.

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Cleaning Knives Infographic

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Sanitizing Knives Infographic

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Storing Knives Infographic

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References

1. U.S. Department of Agriculture (November 15, 2022). Washing Food: Does it Promote Food Safety? https://www.fsis.usda.gov/food-safety/safe-food-handling-and-preparation/food-safety-basics/washing-food-does-it-promote-food
2. Centers for Disease Control and Prevention (No Date). The Difference Between Cleaning, Sanitizing, and Disinfecting. https://www.cdc.gov/hygiene/pdf/331782-a_cleaning_sanitizing_disinfecting_508.pdf
3. U.S. Department of Agriculture (March 24, 2023). Is it safe to use rusty utensils? https://ask.usda.gov/s/article/Is-it-safe-to-use-rusty-utensils