Disclaimer: This post was written while consulting reams of regulatory and industrial food safety documents, but I’m not an expert. If you disagree with anything, please comment with a source so I can research further. Thanks!

Why care about food safety?

The CDC estimates that foodborne illnesses cause 48 million people to become sick, 128 thousand people to become hospitalized, and 3 thousand people to die each year in the US alone.

These illnesses occur after harmful microorganisms (e.g. molds, bacteria, and parasites) or viruses (e.g. norovirus) contaminate food. Norovirus, salmonella, and clostridium perfringens are the most common known pathogens each year, and foodborne illness from unknown pathogens are four times as common. Meanwhile, illnesses such as botulism are infrequent but deadly.

When you consider that the average person in the US is primarily eating consumer goods that have passed the standards of the FDA, these numbers are staggering. With our regular consumption of highly engineered products, it can be easy to carry on without realizing how and why specific foods are safe and for how long.

As a home cook, you probably deviate from FDA guidelines all the time. But you can only be so ambitious before you drive off the rails of presumed safety and enter dangerous territory. That’s where this guide comes in.

Food safety procedures

Contamination from pathogens that cause food spoilage and foodborne illness can occur prior to, during, or after the cooking process. And contrary to popular belief, many of the worst pathogens cannot be seen, smelled, or tasted.

To reduce the chances of food spoilage and foodborne illness caused by these pathogens, you need to both:

1. Kill any existing pathogens in your food. These pose the most immediate risks. You should kill them (or reduce them to safe levels) where possible.

2. Prevent any new pathogens from growing in your food. If you haven’t totally killed the existing pathogens in your food (or if your food is exposed to other pathogens after the fact), the few that remain will multiply over time. This is especially important for foods that you aren’t eating right away (e.g. food you are storing or cooking over multiple hours)

You’re probably familiar with some food safety best practices (e.g. avoiding the temperature danger zone). But you’re probably also aware of seeming contradictions to those best practices (e.g. why can bread or jam be kept in the temperature danger zone?).

In the content that follows, I attempt to equip you with what you need to know to put it all together and make sense of these seeming contradictions.

The primary food safety methods

Specifically, we’ll cover the 4 primary methods for preventing foodborne illness:

1. Cleanliness

2. Temperature control

3. Acidity

4. Water activity

I’ll detail other methods as well in less detail. The guide will start with the most commonly-used methods, though I have a hunch that the later methods (e.g. water activity) will be more useful to my audience. Let’s do it.

1. Food safety Through Cleanliness

This is the most boring and obvious food safety method, but stick with me. This method deserves top billing because it is the best means for preventing norovirus, which is the leading cause of foodborne illness.

Norovirus primarily spreads through surface-level food contamination (e.g. via fruits and vegetables grown in contaminated water or via shellfish harvested from contaminated water) and people (i.e. others already infected with norovirus). For this reason, you should:

• Wash your hands with soap and warm water (as warm as you can tolerate) before handling or serving food. Hand sanitizer works too, but not as well.

• Rinse fruits and vegetables before serving them. Best to do this before prepping or serving rather than after you buy them.

• Clean and disinfect prep surfaces and tools before handling something you’ll serve raw. I disinfect surfaces with this before my pop-ups.

• Avoid handling food while you’re sick.

Note that this advice on rinsing food does not apply to chicken. Washing chicken can actually increase bacteria risk (by spreading salmonella to parts of your kitchen that are not typically heated to salmonella-killing temps).

2. Food safety Through temperature

Temperature can both kill and prevent future growth of harmful pathogens.

To kill existing pathogens

To kill any existing pathogens in your food, you need to heat your food to temperatures that kill those pathogens. Since each food has a unique risk level when it comes to existing pathogens, the temperature you heat your food to depends on the food you’re cooking. Here are a few handy pasteurization temperatures:

• Beef, lamb, and pork: 158ºF or 145ºF held for 4 minutes or 140ºF held for 12 minutes or 130ºF held for 112 minutes

• Chicken, turkey and duck: 165ºF or 140ºF held for 30 minutes or 130ºF for 6 hours

• Fish: 145º or the thickness-specific guidelines here

• Shellfish: 194°F (90°C) for 90 seconds

As you can see, holding foods at specific temperatures for long periods of time enables you to cook food to lower temps (for juicier meat!). Doing so usually requires a sous vide device, but your chicken will thank you!

To prevent the growth of new pathogens

If you haven't completely killed all existing pathogens in your food, or if your food might be contaminated from outside sources, you also need to worry about the growth of new pathogens.

As a rule of thumb, new harmful microorganisms can only grow between 40ºf and 140ºf. That’s why we call that range the temperature danger zone. Food that is not otherwise preserved should stay out of the temperature danger zone (either warmer or colder). If your food must be in the temperature danger zone, it should be there for less than 2 hours total (including the time to warm up or cool down your food).

Breaking the rules

If harmful pathogens are not in your food at dangerous levels, it isn’t necessary to heat your food to pasteurization temperatures. Similarly, if you’ve mastered temperature control, it’s possible to dip below 140ºF for longer than 2 hours.

How? By making smart assumptions about your food. To learn how, check out my deep-dive on temperature control here.

3. Food Safety Through acidity

Harmful microorganisms cannot grow under highly acidic conditions. This is particularly relevant for sauces, drinks, and fermented foods.

To kill existing pathogens

Acidity is not an effective means for killing harmful microorganisms or viruses. To kill existing pathogens in your food, you pretty much need to use temperature. This is why it’s a common misconception that ceviche is “cooked” by citrus juice.

To prevent the growth of new pathogens

Any food substance that measures 4.6 or lower on the pH scale is generally considered acidic enough to prevent growth of harmful microorganisms and can be kept at room temperature.

This is why you can ignore the temperature danger zone for your vinegars (2.5 pH) and lacto-ferments (3.6 pH) with adequate acidity. While acidophile bacteria (like lactobacillus) grow at this temperature, they are generally safe.

If you’re making a dressing, hot sauce, or lacto-ferment, it’s worthwhile to measure the pH before you deem the food shelf-stable. Thankfully, measuring pH is easy and pH strips are super cheap.

Breaking the rules

Understanding acidity and its interaction with other food safety methods can enable you to make tastier preserves with higher acidity. To learn how, check out my deep-dive on food safety with acidity here.

4. Food Safety Through Water Activity

Harmful microorganisms cannot grow with low water activity. This is particularly relevant for low acid foods, dried food products, nut butter, miso, garum, ganache, and jams.

What’s water activity? It’s basically how free the water in a food is to be utilized by other stuff. Picture water in a bowl as totally free, but water in a sponge as partially bound by the sponge. In food, water is usually bound by salt or sugar.

Water activity can be measured (on a scale of 0.0 to 1.0). Most foods have a water activity above 0.95. Meat has a water activity of 0.99 while powdered coffee has a water activity of 0.2.

To kill existing pathogens

Water activity is not an effective means for killing harmful microorganisms or viruses. To kill existing pathogens in your food, you pretty much need to use temperature. To learn how, check out my deep-dive on temperature control here.

To prevent new pathogens from growing

Harmful microorganisms cannot grow with low water activity. Since microorganisms need water to function, when the water in food is bound to other ingredients (such as salt or sugar) in a way that microorganisms can’t utilize it, the microorganisms can’t function.

Generally, items with a water activity level of 0.85 or lower don’t require refrigeration. This is why you can store soy sauce (0.8) and peanut butter (0.7) at room temperature.

To lower water activity in your food

You can decrease the water activity of your food by dehydrating it or adding salt, sugar, or other humectants. Assuming you don’t have a water activity meter to do this accurately, I recommend:

• Dehydrating it! Completely remove the water and then store it somewhere airtight. This is relevant for solid foods.

• Making conservative assumptions. If you assume that your food has the same water activity as water itself, you can follow simple formulas (detailed below) to decrease water activity with salt or sugar. This is particularly relevant for sauces and jams that require salt or sugar anyway.

• Following recipes from a trusted source. Many recipes (especially standard recipes for jam) have stood the test of time because they have adequately low water activity.

I cover specific formulas and assumptions you can make to decrease water activity in my deep-dive here:

5. Food Safety through other means

I’ve described the most common methods that home chefs might use to rid their food of unwanted microorganisms and viruses. But there are other food preservation methods as well:

• Alcohol: High alcohol percentages destroy bacteria. 70% alcohol is enough to destroy many harmful bacteria upon contact. Lower alcohol percentages will prevent future growth, but the specific percentages for this job are very dependent on other factors.

• Packaging techniques: High temperature canning or aseptic packaging techniques are means to create a hermetically sealed environment where no bacteria exist and no bacteria can enter. These techniques involve sterilizing (via heat in excess of 250ºf) both the container and the food inside such that the product can be kept at room temperature until opened. This is essentially the same approach as confit food storage, too.

• Osmosis: Osmosis can destroy certain bacteria. For example, via osmosis, salt helps to destroy certain bacteria in the early days of a lacto-ferment before the acidity has decreased enough to kill the other unwanted bacteria.

• Oxygen or lack thereof: Bacteria and molds are either aerobic (need oxygen) or anaerobic (need absense of oxygen). When you submerge foods in liquids in a lacto-ferment, you’re preventing aerobic bacteria and molds from taking hold. This is partly why a homemade miso might grow mold on the top but not further down. Some of the worst bacteria — such as those that cause botulism — are anaerobic, so I’ve added a section on anaerobic environments below.

On Combining methods

The above techniques can work together to achieve added effectiveness, reduced salinity or acidity, or less stringent temperature requirements. This is how something like shelf-stable low sodium soy sauce is possible.

For example, foods with pH of 5.0 are shelf stable when water activity is 0.9 or lower. See table 4 in this document for more interaction effects.

On anaerobic environments

Botulism is rare, but it can be fatal — so it’s worth spending a bit of time on avoiding the contributing bacteria: clostridium botulinum.

Clostridium botulinum is anaerobic: it needs the absense of oxygen to survive. Cooking environments that lack oxygen include liquids (e.g. brines or oils), sealed cans, and sous vide bags. Any time you store foods like vegetables, fish, and meats in these environments, you need to pay particular attention to time and temperature (or acidity) to prevent clostridium botulinum from taking hold.

To kill clostridium botulinum

Clostridium botulinum dies at much higher temperatures than other harmful bacteria. To reduce clostridium botulinum to safe levels, bring the food to 250ºf (or to 167°f for 520 minutes, 176°F for 75 minutes, or 185°F for 25 minutes).

To prevent the growth of clostridium botulinum

The best way to avoid botulism growth is to keep your food out of the temperature danger zone. This means that storing garlic in olive oil is not a good idea.

Even foods stored in the refrigerator are at risk of future clostridium botulinum growth if the bacteria was not completely destroyed before refrigeration. Foods kept in anaerobic environments should not be kept at at 38°f for more than 30 days or below 36.5ºf for more than 90 days.

Alternatively, you can prevent future bacteria growth by ensuring the food has a pH lower than 4.6. Lacto-fermentation for example is an effective means to prevent botulism in anaerobic environments. Acidity is why you can store that garlic in vinegar with no issues.

On taking risks

I've long believed that good food, good eating, is all about risk. Whether we're talking about unpasteurized Stilton, raw oysters, or working for organized crime 'associates’, food, for me, has always been an adventure.

— Anthony Bourdain

I still eat raw fish when I can buy it fresh. I still use raw egg whites in my cocktails. And I still like my pork chops cooked a lot closer to medium rare than medium.

Ultimately, you can’t eliminate the risk of foodborne illness. But by equipping yourself with an understanding of the possible dangers, you can make more informed trade-offs between danger and deliciousness (or adherence to culture and tradition). And when you’re serving others that might have different risk tolerances, you can adjust your approach as needed. Best of luck, and enjoy the adventure.