Food is supposed to make us healthy and strong. But gone wrong, it can also make us sick or even kill us: chemicals and pathogens can invade our food. That said, there is plenty of good news: here in the U.S. our food infrastructure is generally very safe (so safe that any issue tends to garner a lot of media attention), and some basic knowledge and practices can ensure that as a a cook you’re delivering only safe, healthy nourishment to your family. Food safety is not difficult, and most of it quickly becomes unconscious habit. In fact, there are seven basic steps to safe food:
- Buy ingredients from reliable sources.
- Check expiration dates, both at purchase time and and consumption time.
- Thoroughly wash fresh produce.
- Cook meat, eggs, and fish thoroughly before eating them.
- Don’t let perishable foods sit at room temperature for more than two hours, either before or after cooking them.
- Throw out leftovers after 3-4 days.
- Clean your kitchen regularly and thoroughly.
There are two common risks that form the basis of food safety practices: contamination, and bacterial growth. Contamination occurs when food is delivered to us already tainted with chemicals, waste products, agricultural products such as fertilizers and pesticides, or pathogens (including parasites) — or when food that is otherwise “clean” is cross-contaminated by coming into contact with contaminated food, by being stored together or through shared utensils such as knives and cutting boards. Non-biological contamination such as chemicals that remain on the outside of food can normally be removed from produce by washing it with soap and warm or hot water. Biological contamination will probably require heat to kill it off.
Bacterial growth is inescapable. Bacteria floats in the air around us and inhabits every surface in our homes; even if you perfectly sterilized your entire kitchen, within a very short period of time bacteria would start landing on everything and re-colonizing it. Again, there is plenty of good news here: many bacteria are either not harmful to us or even beneficial. And all bacteria, both good and bad, are very sensitive to temperature and only survive and reproduce in a narrow temperature range. The bad news is that bacteria’s optimal temperature range is also humans’ optimal temperature range: if your house feel comfortable to you, then the bacteria are loving it too.
A big part of food safety is understanding the effect of temperature and heat on bacteria. The higher the temperature, the less time bacteria can survive; and at a high enough temperature — which varies somewhat between strains of bacteria, but is generally between 140 and 165 degrees F — they instantly die. Also, the lower the temperature, the slower bacteria reproduce; and below the freezing temperature of water (32 degrees F) bacteria are unable to reproduce at all. This is an important nuance: until the temperature gets down below about 20 degrees F, cold doesn’t kill bacteria; it just slows down or stops its reproduction (and even below 20 degrees it can take weeks for bacteria to die). Once you take it out of the refrigerator and let its temperature increase, the bacteria will immediately start reproducing again.
Because of this, food safety experts refer to the temperature range between 40 and 140 degrees F as the “danger zone”: food in this range — especially meat, both raw and cooked — is a perfect breeding ground for harmful bacteria. As an aside, this is why hot water tanks are set to 140 degrees: below that temperature, bacteria will grow (especially legionella, the bacteria that causes Legionnaire’s disease).
Conscious of the importance of the “danger zone,” safety experts make the following recommendations:
- Set your refrigerator to about 38 degrees F. About 34 to 38 is fine; above freezing, but cold enough to stay out of the danger zone. Remember that like ovens, refrigerators and freezers have uneven temperature ranges, so test the temperature at several different places, and generally don’t store meat, eggs and fish in the door (the warmest place).
- Set your freezer to around 20 degrees F.
- Cook meat and fish until the internal temperature reaches the point where the bacteria most commonly associated with that food instantly die. Use an insertion thermometer to test the thickest parts to ensure that all parts have reached the necessary minimum temperature.
As mentioned above, the recommended minimum cooking temperature varies for different kinds of meat. For beef, it’s about 140 degrees F; for poultry, it’s 165. Here’s a handy USDA chart with the recommended temperatures; it’s worth printing this out and taping it to the inside of a kitchen cabinet door near your oven so that you can quickly reference it when needed.
The color of meat is NOT an accurate indicator of its temperature; don’t rely on it to tell you when your meat is “done.” A quick-read insertion thermometer is your best friend in the kitchen, and one day could save your life.
Working in the “danger zone”
So we’ve established that we want to store perishable food below 40 degrees F to slow or stop bacteria growth, and we want to cook it to an internal temperature of at least 140 degrees to kill off the harmful bacteria it has picked up along the way. But 140 degrees is too hot to eat (and will scald the inside of your mouth), not to mention far too hot for our kitchen and dining rooms. As we’re prepping, serving and consuming food, we (and it) will inevitably be in the “danger zone.” In fact, as a general rule it’s recommended that raw meat be brought up to room temperature before we begin cooking it. That seems contradictory — what’s up?
Bacteria grow in the “danger zone,” but they don’t grow instantaneously — it takes time. Also, our bodies are good at fighting off small amounts of bacteria, but not large amounts. Food safety experts have done extensive testing on rates of bacteria growth, and based upon that have given us some simple rules to follow on how long it’s safe to have food in the “danger zone.”
Any meat or fish (or milk or juice — anything that provides a good culture for bacteria to grow) that has been sitting at room temperature for two hours or more should be assumed to contaminated with bacteria and thrown out.
Prior to cooking, the time at room temperature is cumulative, and doesn’t have to happen all at once. If it takes you 30 minutes to bring that raw chicken home from the grocery store then stick it in the fridge, it’s still used up one-quarter of its allotted two hours. But you can still take it back out of the refrigerator and safely let it come up to room temperature for half an hour before you cook it.
The rule applies after you cook meat too, though fully cooking it will reset the two-hour limit (because it effectively killed all the prior bacteria); but as soon as cooked meat has cooled down into the danger zone, bacteria will start gathering and multiplying again. If your leftovers sit out for more than two hours, they are no longer safe to eat and you need to toss them.
Needless to say, it’s important to get those leftovers packed up and into the fridge quickly. Also keep in mind that just as food doesn’t heat evenly, it doesn’t cool evenly either. If you put a thick piece of meat — or a tub of hot soup — into the refrigerator, the outer parts will cool down much faster than the inner core. In fact, it’s not too hard to create a situation where part of your food takes longer than two hours to cool down out of the danger zone, even when it’s sitting in your fridge. In commercial settings, cooks are trained to refrigerate food in thin layers so that it cools down as quickly as possible. It’s an important lesson for us when we practice food safety at home: when you put food in the refrigerator, make sure you’ve packaged it so that it can cool quickly.
But we also need to remember that refrigerating food doesn’t kill bacteria; it just slows down its reproduction (which is why fresh food still eventually goes bad in the fridge). Food stays edible longer when refrigerated, but eventually it still needs to be discarded. For leftovers, the general rule is that is something is more than 3-4 days old, toss it.
After cooking with fresh food (and especially meat and fish), cleaning your kitchen is essential so that you don’t cross-contaminate your food the next time you prepare something. That means your countertops, appliances, utensils, tools, pots and pans, cutting knives, cutting boards, and anything else that came into contact with food. It also includes:
- Your sink. Sinks often have pools of room-temperature standing water, the perfect breeding ground for bacteria. And they are the place where we rinse off all the other things that may be contaminated. Start a regular habit of cleaning your sink — including the faucet and handle.
- Your hands. The easiest way to cross-contaminate food is by picking up one thing and then another. Wash your hands frequently while working with food. Also consider using disposable food-prep gloves, especially with dealing with raw meat (and then removing or replacing the gloves immediately after).
- Anything your hands might touch. Cabinet and drawer handles. The refrigerator and oven door handles. The knobs on the stovetop and hood.
- Kitchen towels. Have a bunch of them, and replace them with clean ones every couple of days (or sooner if they get wet).
- Your sponge. Kitchen sponges are truly nasty; they touch everything, and they hold on to room-temperature water. Replace them frequently.
- The floor. Sweep and mop regularly. Spot-clean spills. This will also help keep ants and other pests under control.
Sometimes you will also need to be cleaning as you go while preparing food, especially for things like knives and cutting boards. To avoid cross-contamination, anything that comes into contact with meat or fish — raw or cooked — needs to be thoroughly cleaned with soap and hot water before it is used again. I have multiple cutting boards and mats so that I don’t have to clean them when I’m busy making food; I just put them aside, either “out of play” or directly in the dishwasher, and grab a clean one. Few people have the luxury of enough chef’s knives that they can just put them aside when they get dirty, however, so assume that you will be cleaning yours on the go.
A word on cutting boards: while a new board can be fairly easy to clean by hand, over time and use they can accumulate a lot of ruts and etching. The more “textured” your board gets, the harder it becomes to thoroughly clean it. Keep in mind that cutting boards are not appropriate for family heirlooms, and eventually you will need to throw yours away and replace them.
Checking expiration dates
It took me a long time to get in the habit of checking expiration dates when I buy food at the grocery store, but it’s a very good habit, especially for meat and dairy products. Stores naturally want to sell off of their stock before it expires, so they tend to put the oldest stuff in front or on top and add the new stuff in the back and underneath. It’s always worth digging through a bit to make sure that you’re buying the freshest food available. And you will, from time to time, find food on display that has expired, especially for less common goods that don’t churn through the store very quickly. Also, since we’ve discussed safe temperatures, keep in mind that the food toward the front or top of a refrigerated shelf in a store may not reliably be out of the “danger zone” — or at least not as far out of it as the food farther back or underneath. Make sure that it feels cold when you pick it up.
That said, expiration dates are a bit of a game. Often food is labeled with a “best before” date, rather than an “expires on” date, especially for canned and packaged food that tends to have long shelf-life. Research has shown that in many cases manufacturers and grocers set arbitrarily short “best before” dates in order to encourage you to buy more food.
For fresh meat, if you read meat packaging carefully it often will tell you a much more interesting number than an expiration or “best before” date: it lists the date it was packaged and put on the shelf. I care much more about how long that chicken breast has been sitting there, slowly growing bacteria, than I do when someone has decided that it’s no longer “best.” Often the packaged date isn’t labeled as such, but it’s there nonetheless on the label and it’s pretty easy to figure out.