Unit 9 · Kitchen Safety and Sanitation

Picture a container of leftover rice left on the counter overnight. In the morning it looks fine. It smells fine. It would taste fine. Yet a spoonful of it can hold millions of bacteria, living cells far too small to see, and some of them make poisons that cause vomiting and cramps. Food that makes you sick almost never looks spoiled. That is what makes it dangerous.

Bacteria need four things to multiply: food, moisture, warmth and time. Cooked rice, meat, eggs, dairy, cut fruit and cooked vegetables give them the first two. A warm room gives them the third. Every hour on the counter gives them the fourth. Under good conditions one cell can split into two about every twenty minutes, so a small number becomes a huge number in a few hours.

Sickness from food is called foodborne illness. Common causes include Salmonella, often found on raw poultry and eggs, and E. coli, linked to undercooked ground beef and unwashed produce. Symptoms may take hours or days to show up, so the meal that made you sick is often not the last one you ate.

You cannot see bacteria, so you cannot check food by looking. Instead, you control the four things they need. The rest of this chapter is four habits that do exactly that: clean, separate, cook and chill. Learn them once and you will use them for the rest of your life.

Open a refrigerator and put a thermometer inside. It should read 40 °F or lower. Now think about a pot of soup on the stove, steaming at well over 140 °F. Between those two numbers is the danger zone: 40 to 140 °F. In that range, bacteria multiply quickly. Below it they slow down; above it they die off as food cooks.

Almost every room in a house sits inside the danger zone. A kitchen at 72 °F is right in the middle of it. That is why the counter is the worst place to keep food that needs to stay cold or hot. The fridge is below the zone. A hot oven or a warming tray is above it. The table at a picnic is inside it, and on a summer day it is deep inside it.

The fridge works only when it is truly cold. Set it at or below 40 °F and check it with a small fridge thermometer, because the dial on the door does not show degrees. The freezer should read 0 °F. Freezing does not kill bacteria; it stops them from growing. When frozen food thaws into the zone, they start growing again.

Keeping food out of the zone is the idea behind most of the rules you will learn. Chill leftovers fast. Cook meat all the way. Do not thaw on the counter. Each rule is one way of moving food through 40 to 140 °F as quickly as possible, or keeping it out entirely.

Think of the chicken on the counter after dinner. Dishes take a while, someone gets a phone call, and the chicken sits. The rule is simple: perishable food, meaning food that spoils, may stay in the danger zone for no more than two hours total. After that, throw it out. Do not taste it to check. Do not reheat it to fix it. Out.

Two hours is the limit for a normal room. When the air is above 90 °F, at a picnic, in a hot car, or on a porch in July, the limit drops to one hour. Bacteria grow faster in a hotter room, so they use up the safe time faster. The potato salad in the story sat for four hours at 92 °F, four times its limit.

The clock is a running total, not a fresh start. If the milk sat out for an hour at breakfast and an hour at lunch, its two hours are gone. To keep track, set a timer when food comes out of the fridge. A twenty-minute lunch is not a problem. A bowl left out through a whole movie is.

Perishable foods include meat, poultry, fish, eggs, dairy, cooked rice and pasta, cooked vegetables, cut fruit and anything made with them. Dry crackers, whole uncut fruit, bread and unopened cans are not. At a picnic, keep the perishables in a cooler with ice until the moment they are served, then put them back.

Stand at the sink. Wet your hands with clean running water, turn the water off, and apply soap. Rub your palms, the backs of your hands, between your fingers and under your nails for a full twenty seconds, about the time it takes to hum "Happy Birthday" twice. Rinse under running water and dry with a clean towel or a paper towel. That is a hand wash. Anything shorter is a rinse.

Wash before you start cooking, after touching raw meat, poultry, fish or eggs, after using the bathroom, after touching your face, hair or phone, after handling trash, and after touching a pet. In a cooking lab that means washing several times in one class, and that is normal. Hand sanitizer is a backup for when there is no sink, but it does not remove grease or dirt the way soap does.

Surfaces need the same care. Before you begin, wipe the counter and cutting boards with hot soapy water. After raw meat touches a surface, wash it again with hot soapy water and then sanitize it, which means treating it to kill the bacteria that washing left behind. A common home sanitizer is a solution of a small amount of unscented bleach in water; follow the label.

Sponges and dish towels are a hidden problem. A damp sponge is warm, wet and full of food, all four things bacteria want. Use paper towels to clean up raw meat juices, change dish towels often, and let sponges dry out between uses or replace them. Tie back long hair, take off rings and bracelets, and wear an apron, so that you are not adding to the counter what you just cleaned off it.

Take a head of lettuce and an apple. Even if you will peel the apple, rinse it first under cool running water and rub it with your hands. Otherwise the knife drags whatever is on the peel into the fruit. Pull the lettuce leaves apart and rinse each one, then dry them in a spinner or on a clean towel. Firm produce like potatoes and carrots can be scrubbed with a clean vegetable brush. Do not use soap; produce is not made to be eaten with soap on it.

Rinse produce right before you use it, not before you store it. Wet berries in the fridge grow mold. Cut the bruised or damaged spots away. Packaged salad marked "prewashed" or "ready to eat" does not need another rinse. Melons deserve special care: scrub the rind before cutting, because the knife carries anything on the outside straight through the sweet, wet inside.

Dishes get washed in a set order so the water stays clean as long as possible. Scrape food into the trash first. Fill the sink with hot, soapy water. Wash the least greasy items first: glasses and cups, then silverware, then plates and bowls, then pots and pans, and cutting boards that touched raw meat last of all. Rinse in hot water and let dishes air-dry in a rack, or dry them with a clean towel.

A dishwasher does the same job with hotter water than hands can stand, which is why it is a good place for cutting boards and knives that are dishwasher-safe. Cutting boards with deep knife grooves are hard to clean and should be replaced. Wooden boards should never soak; they crack, and cracks hold bacteria.

Picture a cutting board. Someone slices raw chicken on it, sets the chicken in the pan, and then slices tomatoes for a salad on the same board. The chicken is going to be cooked to 165 °F, so its bacteria will die. The tomatoes will not be cooked at all. Every germ the board picked up from the chicken now rides on the salad. This is cross-contamination: bacteria moving from one food, surface or hand to another.

Raw meat, poultry, fish and eggs are the usual sources. Ready-to-eat foods are the usual victims: salads, fruit, bread, cooked dishes, anything that will not be heated again before it is eaten. The rule is to keep the two groups apart at every stage: in the cart, in the fridge, on the counter, on the plate.

Cross-contamination happens through surfaces, through tools and through hands. A knife used on raw meat and then on cheese. A plate that carried raw burgers to the grill and then the cooked ones back. Tongs that flipped raw chicken and then served the cooked pieces. Hands that touched raw meat and then the fridge handle, the salt shaker and the bag of rolls.

The fix is a separate tool or a wash between uses. Two cutting boards, two plates, two sets of tongs, or one of each washed in hot soapy water in between. Never rinse raw poultry in the sink; the water splashes bacteria onto the counter, the faucet and the dishes nearby. Cooking kills the bacteria on the chicken anyway.

Many kitchens use color-coded cutting boards. One common scheme uses red for raw meat, yellow for raw poultry, blue for fish, and green for produce. Any scheme works as long as everyone in the kitchen uses the same one. At home, two boards are enough: one that only ever sees raw meat, poultry and fish, and one for everything else. Write it on the board if you have to.

Plates and tools follow the same idea. Carry raw burgers to the grill on one plate and bring the cooked burgers back on a clean one. Never put cooked food back on the plate that held it raw. Marinade that soaked raw meat cannot be served as a sauce unless it is boiled first; it is simpler to set some aside before it touches the meat.

The refrigerator has an order too. Raw meat, poultry and fish go on the bottom shelf, on a plate or in a container that catches drips. Ready-to-eat food goes above them. That way a leaking package of chicken drips onto the shelf below, not onto the strawberries. Eggs stay in their carton on a shelf, not in the door, because the door is the warmest spot.

At the store, the same rule applies. Put raw meat in the plastic bags the store provides, keep it apart from produce in the cart, and bag it separately at checkout. On the way home, it should be the last thing in the cart and the first thing in the fridge.

Cut into a chicken thigh and the juices run clear, so it must be done, right? Not always. Color and juices are unreliable; some poultry stays pink at a safe temperature and some ground beef turns brown before it reaches one. The only way to know is a food thermometer. A digital instant-read thermometer costs about the price of a fast-food meal (example) and reads in a few seconds.

To use one, push the probe into the thickest part of the food, away from bone, fat and the pan. Bone heats faster than meat and gives a false high reading. For a thin burger, slide the probe in from the side so the tip reaches the middle. For a whole chicken, check the thickest part of the thigh and the thickest part of the breast. Wait for the numbers to stop moving.

Check the thermometer itself now and then. Fill a glass with crushed ice, top it with water, stir, and put the probe in without touching the sides. It should read 32 °F. If it does not, many thermometers have a small nut behind the dial or a reset button to adjust it. A thermometer that reads wrong is worse than none, because it makes you confident.

Wash the probe in hot soapy water after every use, especially between checking raw and cooked food. Pushing a probe that touched raw chicken into a cooked burger is cross-contamination with extra steps. Keep the thermometer where you can reach it; the one in the back of the drawer never gets used.

Here are the numbers, and they are worth memorizing. Poultry of every kind, whole, pieces or ground: 165 °F. Ground beef, pork, lamb and veal: 160 °F. Whole cuts of beef, pork, lamb and veal, such as steaks, chops and roasts: 145 °F, followed by a three-minute rest before cutting. Fish: 145 °F, or until the flesh is opaque and flakes with a fork. Egg dishes: 160 °F, and plain eggs cooked until the yolk and white are firm. Leftovers and casseroles reheated: 165 °F.

Why is ground meat higher than a steak? On a whole steak, bacteria live on the outside surface, which hits high heat first. Grinding mixes the outside all through the inside, so the center of a burger needs to reach 160 °F. A burger cooked to 145 °F is not safe just because a steak at 145 °F is. Poultry carries Salmonella so often that its number is the highest of all.

The three-minute rest for whole cuts is part of the cooking, not a suggestion. Take the roast out at 145 °F, cover it loosely with foil and leave it three minutes. The heat inside keeps working, and the juices settle so they do not run out when you slice. Reheating is easy to forget: leftovers must reach 165 °F all the way through, so stir them halfway and check the center, not the edge.

Microwaves cook unevenly, leaving cold spots where bacteria survive. Cover the food, stir or rotate it partway through, and let it stand a minute before checking the temperature. When a package says "cook until steaming hot," that is a rough guide. The thermometer is the real test, and 165 °F is the real target.

A frozen chicken sits on the counter all day so it will be ready for dinner. By afternoon the outside has been in the danger zone for hours while the middle is still ice. That is the problem with counter thawing: the surface, where bacteria live, warms up first and stays warm longest. The counter is never a safe place to thaw meat, poultry or fish.

There are three safe ways. The first is the refrigerator. Put the frozen food on a plate on the bottom shelf and let the fridge do the work. It is slow, about a day for a package of chicken pieces and longer for a large roast, so plan ahead. Food thawed this way can stay in the fridge a day or two before cooking and can even be refrozen, though it may lose some quality.

The second is cold water. Seal the food in a leakproof bag, submerge it in cold tap water, and change the water every 30 minutes so it stays cold. A pound of meat takes about an hour; larger packages take longer. Cook the food right away once it thaws. The third is the microwave on its defrost setting, which warms parts of the food into the danger zone, so cook it immediately afterward.

You can also skip thawing. Frozen meat and poultry can go straight into the oven or onto the stove; it just takes about half again as long to cook, and you must still check it with a thermometer. What you cannot do is leave it in the sink, in hot water, or on the counter and hope.

Dinner is over and a big pot of chili is still on the stove. The old advice was to let it cool before it goes in the fridge, but a deep pot of hot chili can take many hours to cool, all of it in the danger zone. The rule now is the two-hour rule again: leftovers go into the fridge within two hours of cooking, and warm food is fine to put in.

The trick is shallow containers. Divide the chili into containers no more than about two inches deep so the cold reaches the middle quickly. Leave the lids loose until it stops steaming, then seal. Label each with the food and the date. Do not stack hot containers on top of one another; give them room for cold air to move.

Use refrigerated leftovers within about three to four days. If you will not eat them by then, freeze them; frozen food stays safe for a long time, though quality fades. Reheat leftovers to 165 °F, stirring so there are no cold spots. Reheat only what you will eat; food that has been reheated and cooled more than once has spent extra time in the danger zone.

A clean, cold fridge is the last piece. Wipe up spills right away. Do not pack it so full that air cannot move, because a crowded fridge has warm pockets. Keep a thermometer inside and check it: 40 °F or below. When you are not sure how old something is or whether it was handled safely, the rule is short and worth repeating: when in doubt, throw it out.

Lift the lid off a pot of boiling pasta and tilt it toward you. The steam that rolls out is over 212 °F and it burns skin instantly. That is a scald, a burn from hot liquid or steam, and it is the most common kitchen injury. Always lift a lid away from your face, so the steam escapes on the far side. Open the oven door partway and wait a second before leaning in.

Handles are the next problem. A pot handle sticking out over the front of the stove is a handle someone will hit with an elbow. Turn every handle toward the back or the side, over the counter, not over another burner. A metal handle on a skillet that has been in the oven is as hot as the oven. Leave the mitt on it, or drape a towel over it, so the next person knows.

Use dry oven mitts or pot holders, never a wet towel; water in the cloth turns to steam against your hand. Set hot pans on a trivet or a cooling rack, not on the counter or on a plastic cutting board. Pull the oven rack out to reach a dish instead of reaching into the oven. When you add food to hot oil, lower it in with tongs so it does not splash.

Microwaves cause their own burns. A bowl can be cool while the food inside is far hotter, and liquids heated too long can boil up suddenly when moved. Let food stand a minute, stir it, and take it out with a mitt. Keep small children away from the stove entirely, and keep the cords of kettles and slow cookers pushed back where nobody can pull them.

A dull knife slides off a tomato skin and into a finger. A sharp knife bites in where you point it. That is why a sharp knife is the safer one: it takes less force, so it does not slip. Keep the board from sliding by laying a damp towel under it. Curl the fingers of your holding hand into a claw so the knuckles, not the fingertips, face the blade.

Cut on a board, never in your hand. Cut away from your body. Never try to catch a falling knife; step back and let it land. Carry a knife at your side, point down, blade toward the back, and tell people "knife behind you" when you pass. Never leave a knife in a sink of soapy water where a hand will find it by accident. Wash it, dry it and put it away.

Other sharp things hide in the kitchen: the lid of an opened can, the blade of a blender or food processor, a box grater, a broken glass. Sweep broken glass with a broom, not your fingers, and wrap it in newspaper before it goes in the trash. Unplug a blender before you reach into it, and wash its blade separately, holding the base.

Falls happen on wet floors and from chairs used as ladders. Wipe up every spill the moment it happens, water or grease, and say "spill" so nobody steps in it. Use a step stool with a handrail to reach a high shelf, not a chair and not the counter. Keep cabinet doors and drawers closed. Tie shoelaces, and wear closed-toe shoes in a lab, because a dropped knife or a splash of oil lands on feet.

A toaster with a slice stuck in it, and a fork in someone’s hand. The metal fork touches the heating element and the current runs up the fork into the person. Always unplug an appliance before you reach into it, fix it, or clean it. Then use wooden tongs for the toaster, and let it cool.

Water carries electricity. Never plug in or unplug anything with wet hands, and never use an appliance near a full sink. If a plugged-in appliance falls into water, do not reach for it. Unplug it first, or turn off the circuit breaker if you cannot reach the plug safely. Kitchens have special outlets called GFCI outlets, with test and reset buttons, that shut off power in a fraction of a second when they sense a fault. Test them monthly.

Cords cause accidents in two ways. A cord that hangs over the counter edge is a cord a child or a dog can pull, bringing a kettle of boiling water down with it. A cord that lies across a hot burner melts, and a melted cord can shock or start a fire. Route cords along the back of the counter. Pull plugs out by the plug, not by the cord, so the wires inside stay attached.

Look at cords before you use them. Frayed insulation, exposed wire, a plug that is warm or scorched, or an appliance that buzzes, smells hot or sparks all mean stop, unplug and tell an adult. Do not overload one outlet with a power strip full of high-heat appliances; a toaster oven, a kettle and a microwave together can trip a breaker or heat the wiring.

Oil in a pan can get hot enough to light itself. When it does, you have seconds, and the first move is the burner: turn it off. The second move is to cut off the air. Take a metal lid or a baking sheet, hold it with a mitt, and slide it over the pan from the near edge, keeping your arm out from over the flames. No air, no fire. Leave the lid on until the pan is completely cool.

If there is no lid, pour baking soda on a small fire. A lot of it, not a pinch. Baking soda releases carbon dioxide when heated, which smothers the flames. Salt also works by smothering. Never use flour, sugar or baking mix; fine powders can ignite in the air and turn a small fire into a fireball.

Never, ever use water. Water is heavier than oil, so it sinks under the burning grease, boils instantly and blasts flaming oil out of the pan and across the kitchen. Do not carry the burning pan to the sink or outside either; the flames blow back on you and the oil sloshes. The pan stays where it is.

If the lid and the baking soda do not work, or if the fire has spread past the pan to a cabinet or a curtain, it is no longer a pan fire. Get everyone out, close the door behind you and call 911 from outside. A kitchen fire extinguisher is for a fire still small enough to face; the next lesson shows how to use one. Prevention is easier: never leave hot oil unattended, heat oil on medium, and keep a lid within reach every time you fry.

Find the fire extinguisher in your kitchen or lab right now, before you need it. It should be near an exit, not behind the stove where the fire would be. Read the label: a home kitchen extinguisher is usually rated ABC, meaning it works on ordinary materials (A), flammable liquids like grease (B) and electrical fires (C). Restaurant kitchens use a Class K extinguisher made for deep fryers.

The steps spell PASS. Pull the pin at the top of the handle. Aim the nozzle at the base of the fire, not the flames, because the fuel is at the bottom. Squeeze the handle. Sweep the nozzle side to side across the base until the fire is out. Stand about six to eight feet back to start and move closer as the fire dies down.

Before you use it, make two decisions. Is the fire small, meaning no bigger than a wastebasket, and not spreading? And is the exit behind you, so you can back out if it grows? If either answer is no, do not fight the fire. Leave, close the door, and call 911. An extinguisher empties in seconds; it gets one try.

Afterward, watch the spot for a few minutes in case it lights again, and open windows to clear the powder. Even a partly used extinguisher must be replaced or recharged. Check the gauge on any extinguisher once a month: the needle should sit in the green. Install a smoke alarm near the kitchen and test it monthly too; most kitchen fires start on the stove, and most are found early by a working alarm.

The most common cause of kitchen fires is a stove left alone. Oil heats faster than people expect, a towel slides onto a burner, a pot boils dry. The rule is simple: if you are frying, grilling or broiling, stay in the kitchen. If you leave the room, turn the burner off. Set a timer for anything simmering or baking so it cannot be forgotten.

Keep the cook zone clear. Nothing that can burn within three feet of the stovetop: no towels, paper, oven mitts, plastic bags, wooden spoons or cereal boxes. Wear short or rolled sleeves. Clean grease off the stovetop and out of the range hood filter, because old grease is fuel. On a gas stove, if you smell gas and the burner did not light, turn the knob off, do not light anything, and open a window.

Ovens have their own rules. Open the door and stand to the side for a second before leaning in. If something catches fire inside the oven, keep the door closed and turn the oven off; the fire will smother itself. The same goes for a fire inside a microwave: keep the door shut, turn it off, unplug it. Do not put metal in the microwave, and do not run it empty.

Small appliances like toaster ovens, air fryers, slow cookers and electric kettles get hot on the outside too. Give them space from the wall and from each other, unplug them when they are not in use, and never wrap the cord around a hot unit. Know where the stove knobs are without looking, and where the breaker panel is. In an emergency, you shut things off by feel and by memory, not by reading.

The knife slips and there is blood on the board. First, stop and put the knife down. Wash your hands if you can, then press a clean cloth or paper towel firmly on the cut. Steady pressure is what stops bleeding. Hold it, do not peek every few seconds, and raise the hand above the heart if you can. Most small cuts stop within a few minutes.

Once the bleeding slows, rinse the cut under clean running water to wash out anything in it. Do not use hydrogen peroxide or alcohol inside the wound; they damage the tissue. Pat it dry with a clean cloth, apply a thin layer of antibiotic ointment if you have it, and cover it with a clean bandage. In a food lab, cover the bandage with a disposable glove before touching food again.

Some cuts need a doctor. Get help if the bleeding does not stop after steady pressure, if the cut is deep or gaping, if it is on the face or over a joint, if something is stuck in it, or if it came from a dirty or rusty object. Bleeding that spurts or soaks through a cloth is an emergency; call 911 and keep pressing.

The food on the board is done. Anything the blood touched goes in the trash, and the board, the knife and the counter get washed and sanitized before work continues. Tell the teacher or an adult about every cut, even a small one. Write it down if the lab keeps an injury log; the point is not blame but finding the pattern that caused it.

A hand brushes the oven rack. The skin turns red and starts to sting. Get it under cool running water right away, from the tap, not ice cold, and keep it there for at least ten minutes if you can. Cooling stops the heat from going deeper into the skin. Take off rings or watches near the burn before it swells.

Do not use ice; it damages burned skin further. Do not put on butter, oil, toothpaste or grease, which trap the heat in and can cause infection. After cooling, cover the burn loosely with a clean, dry cloth or a sterile non-stick dressing. Do not pop a blister; the skin over it protects the raw layer underneath.

Burns are graded by depth. A first-degree burn is red and painful, like a mild sunburn. A second-degree burn blisters. A third-degree burn looks white, leathery or charred and may not hurt at all because the nerves are damaged. Any burn larger than the palm of your hand, any burn on the face, hands, feet or a joint, and any third-degree burn needs a doctor, and a large or deep burn means 911.

For a scald from hot liquid soaked into clothing, get the clothing off fast unless it is stuck to the skin; the wet cloth keeps burning. For a grease splash, same rule: cool water, then cover. Report every burn to the teacher. Then look at what caused it, because the fix for a burn is almost always something you can change next time: a mitt, a handle turned in, a lid tilted the other way.

The hardest part of an emergency is deciding it is one. Call 911 when a fire is not out after the lid, when someone cannot breathe or is choking and cannot cough, when bleeding spurts or soaks through cloth, when a burn is large or deep, when someone is unconscious, or when someone has swallowed a chemical. If you are not sure, call. The dispatcher would rather answer a call that was not needed than miss one that was.

Know your address before the emergency. In a school lab that means the school name, the street, and the room number. On the phone, say where you are first, then what happened. Stay on the line; the dispatcher will tell you what to do while help is coming. Speak slowly. Send someone to the door to wave the ambulance in.

For choking, the sign is a person who cannot speak, cough or breathe and may grab their throat. If they can cough, let them cough. If they cannot, call 911 and, if you are trained, give back blows and abdominal thrusts. First-aid training from the Red Cross or a similar group teaches this and CPR in one afternoon, and every kitchen worker should have it.

Keep a list where everyone can see it: 911, the Poison Control number, the school office or a parent’s number, and the address. Keep the first aid kit stocked and in a marked spot. Practice matters. A class that has walked through "what would we do if" acts in seconds, and seconds are what a kitchen emergency gives you.

A friend at your table takes a bite of a cookie and, within minutes, her lips swell and her breathing sounds tight. That is a food allergy: the body’s defense system treats a harmless food as an attacker. Reactions range from hives and an itchy mouth to anaphylaxis, a whole-body reaction that closes the airway and drops blood pressure. Anaphylaxis can kill within minutes.

In the United States, nine foods are the major allergens named by law: milk, eggs, fish, crustacean shellfish such as shrimp and crab, tree nuts such as almonds and walnuts, peanuts, wheat, soybeans and sesame. Sesame was added to the list in 2023. These nine cause most serious reactions, though a person can be allergic to almost anything.

The amount does not have to be large. For some people, a knife that spread peanut butter and was wiped on a towel carries enough peanut to cause a reaction. That is why allergens are handled like raw chicken: separate tools, separate boards, hands washed with soap and water, and surfaces scrubbed. Hand sanitizer does not remove allergen proteins; soap and water do.

Many people with severe allergies carry an epinephrine auto-injector, a pen-shaped device that injects a dose of medicine into the thigh. If someone is having a serious reaction, help them use it, then call 911, because the medicine wears off and a second reaction can follow. Ask about allergies before you cook for anyone, and take the answer seriously. "A little won’t hurt" is not true.

Pick up a package of granola bars and turn it over. Under the ingredient list there is often a line in bold: "Contains: milk, peanuts, soy." U.S. law requires packaged foods to name any of the nine major allergens in plain words, either in the ingredient list or in a Contains statement right below it. "Whey" must be labeled as milk; "albumin" as egg.

Some labels add a line such as "May contain tree nuts" or "Made in a facility that also processes peanuts." These advisory statements are voluntary and mean the food could have picked up traces on shared equipment. For someone with a severe allergy, that is a reason to skip the product. Never assume; a food with no advisory line is not promised to be trace-free.

Read the label every single time, even on a food you have bought a hundred times. Companies change recipes, and the new version can add an allergen without changing the front of the box. Read it at the store, and read it again before you cook. In a lab, keep the packages until the food is served so the label can be checked if someone asks.

Allergens hide in unexpected places. Soy in bread and chocolate, milk in deli meat, egg in some pasta and salad dressings, wheat in soy sauce, fish in Worcestershire sauce, peanuts in some chili and mole sauces. If a dish is for someone with an allergy and you cannot read a label for every ingredient, do not serve it. Say so plainly. A missed meal is nothing compared to a missed allergen.