Even if you're not a market refrigeration tech, we all know that the primary function of refrigeration is to keep food cool. Easy, right?

Even though food storage sounds pretty simple, there are a lot of things we should keep in mind when we think about food safety and quality. There’s a lot more to storing food than sticking it in a cooler or freezer until a customer is ready to buy it. And then we have to store food safely in our own fridges and freezers until we’re ready to cook or eat it.

We must keep food safety and quality in mind when storing refrigerated and frozen food (or working on those refrigeration systems). There are safe temperatures and storage guidelines that we must follow, and we'll explore some of those in this tech tip, as well as the risks of not following them. We’ll also cover some defrost considerations and the ideal storage temperature and relative humidity for common foods.

Foodborne Illness Prevention 

The main reason why we refrigerate most food is to keep it safe and prevent us from getting sick. There are a few ways we can get sick from food. 

Believe it or not, mold by itself isn’t likely to make you very sick (unless you’re allergic to it, of course). You still don't want to eat moldy food (unless the mold is supposed to be there, like in the case of blue cheese), but we're more concerned about the bacteria and toxins that may live on the mold or be produced by some varieties. The main causes of food poisoning are bacteria, so we’ll look at a few common types we want to avoid.

Some common bacteria that cause foodborne illnesses are Salmonella, E. coli, and C. botulinum. The US Food & Drug Administration (FDA) has a longer, more thorough list, but here’s a quick overview of what those three bacteria can do to your body and how they enter it:

Salmonella causes an infection (salmonellosis) that comes with nasty stomach flu-like symptoms and may be fatal in some cases. Animal products such as meat and eggs are the most common sources of Salmonella, but Salmonella can also live on vegetables exposed to contaminated soil or water.

The O157:H7 strain of E. coli is a common cause of food recalls. The infection that results from E. coli food poisoning is rarely fatal for healthy adults, but stomach flu-like symptoms are common, and complications such as kidney failure are possible. The most common E. coli outbreaks have been associated with raw or undercooked beef and leafy greens.

Clostridium botulinum can cause a rare but fatal disease called botulism. According to the Mayo Clinic, foodborne botulism symptoms are a mix of gastrointestinal and neurological symptoms and include stomach upset and cramps, vomiting, facial weakness, blurred or double vision, and paralysis. The most common foods that may harbor C. botulinum are improperly canned vegetables and fermented fish.

The Importance of Proper Refrigeration

The good news is that proper refrigeration can reduce the risk of all of these bacterial infections. Cold temperatures inhibit the growth of microorganisms that cause foodborne illness. The recommendation is to keep refrigerator temperatures at or below 40° Fahrenheit (4° Celsius).

However, refrigerating food doesn't inactivate the microbes, so most refrigerated foods still need to be used within their recommended lifespan or thrown away if spoiled. It’s also worth noting that some bacteria and mold may still grow in refrigerators. Listeria can grow on lunch meats and unpasteurized milk products at 40°F, so some foods may have slightly lower temperature recommendations.

Freezing food eliminates the risk of microorganism growth and food spoilage. Freezer temperatures at or below 0°F (-18°C) will inactivate all microbes. (Note: microorganisms can activate again upon thawing.)

There’s more to it than temperature, though. Air circulation is also vital to proper refrigeration.

Some of us come home from the grocery store and pack all the refrigerated items in our fridges or freezers as tightly as possible. “Refrigerator Tetris” may be fun for some people, but there's a drawback to cramming lots of food together. When refrigerated items are packed too tightly, it’s difficult to maintain a constant temperature because the air can’t circulate as well as it should—your risk of microbial contamination increases.

Freezing Food 

Freezing food inactivates bacteria and fungi on your food. That's great, but how long can food last in a freezer before spoiling?

The answer: you can store food in a freezer indefinitely to avoid spoilage. However, just because you can doesn’t mean you should.

There’s a reason why there are charts all over the internet with recommended freezer durations for certain foods. Food safety is not the issue. Food quality is. Some foods may smell or taste bad when left in the freezer for long periods, even though there isn’t a risk of microbial contamination. 

Some foods also don’t freeze well. While you can freeze pretty much anything except canned foods and shelled eggs, it’s not a good idea to freeze cream sauces, mayonnaise, lettuce, and cottage cheese if you don’t want poor-quality food. Sour cream, yogurts, and other refrigerated dairy products also tend to separate when frozen, making them feel strange and taste bland.

Proper refrigeration is important for maintaining food safety and quality. Freezers may deliver on the safety part, but they may seriously reduce food quality, especially over longer periods. Even though it won't hurt you, nobody likes freezer-burnt food.

Defrost Cycles

Frost buildup is a fact of life for refrigeration systems. So while defrosting is critical for proper refrigerator functioning, we have to be very careful because improper defrost cycles can overheat food and lead to spoilage or reduced quality.

There are a few controls and strategies you can use to facilitate the defrosting process. We’ll briefly cover a few common ones.

Some automatic defrost systems come with an electric heater that turns on during a defrost cycle and heats the evaporator coils. When the cycle ends, the heater shuts off again. Many refrigerators also have gas solenoid valves, which reverse the refrigeration cycle to send hot gas to the evaporator. The hot gas heats the coils from the inside, causing the surrounding ice to melt. Otherwise, defrosting happens on an off-cycle where everything shuts down, but this only works in coolers, not freezers.  For more detailed information on defrosting controls and strategies in commercial refrigeration, check out our podcast episode on it with Dick Wirz.

Time and frequency are the most critical elements to watch when defrosting. Regardless of the defrost method, the goal of defrost is always the same: melt ice off the evaporator coils with minimal variation in the product and box temperatures. To achieve this goal, defrosts should be as short and infrequent as possible. Excessively long or frequent defrosts will cause the case to overheat, leading to improper storage conditions that increase the product temperature. Warming products can result in reduced quality (and possibly safety).

Recommended Storage Temperatures

Different foods have different ideal storage temperatures. We’ve prepared a table of common foods and their storage temperatures. (Sources: California Department of Education, Cornell Cooperative Extension, and the New York Division of Military and Naval Affairs.)

NOTE: If you do grocery refrigeration, follow the guidelines of your customer rather than this.

Humidity

Did you notice that the produce is split into categories? Cornell University divided fruits and vegetables into four storage groups based on temperature and humidity needs, and I used that same classification system here. 

It’s reasonable to expect that watermelon would require a different set of humidity needs than garlic, so you also have to take that into account when you store fresh food. It’s not just with produce either; relative humidity affects the quality of fresh meat as well. Meat kept in dry conditions could lose weight, which does not affect the product's wholesomeness but will negatively affect the texture and taste.

We’ve also put together a relative humidity chart for fresh foods. (Sources: Cornell Cooperative Extension and the Food and Agriculture Organization of the United Nations.)

Cornell University’s Cooperative Extension has a thorough resource for vegetable storage and has more detailed temperature and humidity information on specific fruits and vegetables.

 

As you can see, food storage is nowhere near as simple as sorting your groceries into your fridge, freezer, or pantry. In general, temperatures below 40°F will keep most refrigerated food safe enough for its recommended duration in the fridge, but that doesn’t mean that temperature is appropriate for preserving quality for all foods. The same goes for the amount of time food stays in a freezer. Food may be safe from bacterial and fungal growth at subzero temperatures (Fahrenheit), but that doesn’t mean that it’ll retain its quality.

There are some excellent charts out there for food storage best practices, and we hope you’ll use them to keep your families and customers safe and satisfied. As I said earlier, Cornell Cooperative Extension’s vegetable storage guide is a good place to start. Other resources include the New York Division of Military and Naval Affairs storage guide and the University of Georgia’s Cooperative Extension consumer’s guide.