How can you slow cook food for several hours and not get food poisoning from it?

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I thought that heating uncooked food at a temperature above 135 degrees F for a relatively short amount of time and then keeping it cold right after was the only way to prevent food from making you sick, but I don’t understand how people can cook “low and slow” stews or crockpot food that’s been cooking for like 8+ hours and eat them without any problem.

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When food enters the kill zone/cooking zone, the bacteria die. Food can sit at whatever temperature it wants for however long it wants (from a bacteria standpoint, not a material degradation standpoint) as long as you then heat it enough to kill the bacteria after, which happens at the end of low and slow.

Slow cookers and crock pots “slow cook” the food typically in excess of 150 F for the duration. So it is pretty difficult for food to spoil due to bacteria at that temperature.

It heavily depends on the food, the pre-cook method, and how much risk you are willing to accept. There are simply too many possibilities to name them.

As a general rule, the US government has declared that 135°F will make near all food safe to consume (with certain meats needing to be higher: https://www.foodsafety.gov/food-safety-charts/safe-minimum-internal-temperatures), based on the most dangerous microorganisms that can live in food.

This doesn’t mean that the dangerous stuff is guaranteed to be in your food every time. It is also not guaranteed that 135°F is enough. With as clean and reliable as our food can be, and with proper storage and prep practices, it is more likely that your food does not have dangerous microorganisms. But, are you willing to risk it?

Bacteria and other pathogens start to die at around the temperature you said (135°F) and even a bit below that actually. If you hold food at that temperature for long enough, you will kill off nearly all bacteria that are there (you never kill of 100% but it’s enough to kill 99.9999% or something like that) and the food will be safe to eat. Holding food at a temperature that high (or higher) for longer will only make it **safer**, not less safe.

Temperatures between 40-140°F are usually referred to as the “danger zone”, where pathogens can grow. Now, I just told you pathogens actually start to die at temperatures as low as 135°F. So what gives? Well, what I said is true, but it does require that you are able to control the temperature reliably enough that it won’t dip to, say, 120°F for long periods of time. Official recommendations don’t want to skirt to close to the edge of what’s safe, so they build in a margin of error and put the boundary at 140°F.

Similarly, official recommendations often tell you to heat meat to an internal temperature of 160°F in order to render it safe for eating. Again, that’s to be extra safe, because at that temperature, pathogens are killed off (to safe levels) pretty much instantly. At lower temperatures, like 135°F, it takes longer to reduce the amount of pathogens to a safe level, so it takes more effort, control and precision. It’s also worth noting that lots of foods are habitually cooked to lower internal temps without serious consequences. If you like a medium-rare steak, that steak’s core internal temp hasn’t gone above 135°F (or thereabouts). and if cooked traditionally, it wasn’t held at that temperature for more than a few minutes. So it’s not guaranteed to be safe. However, beef is unlikely to contain parasites, and bacteria don’t tend to penetrate into an intact muscle of beef, staying mainly on the surface. All of which means that you can eat a medium-rare steak with minimal risk of food-borne illness.

Low-and-slow cooking techniques actually typically don’t skirt close to the danger zone anyway, unless you’re talking about something like sous vide cooking. The cooking temperatures are usually well in excess of 160°F, at which point all pathogens are destroyed anyway. Holding food at these temperatures will only pasteurize it further, so regular slow-cooking is actually an incredibly safe way to prepare food, as long as you do it right. (There is a slight risk that e.g. your slow-cooker develops a fault mid-way through the cooking process and then the food hangs out at unsafe temperatures for hours. Although, if the food had already been held at instant-pasteurization temperatures for hours before that, it will likely still be fine as long as you don’t wait too long before eating it.)

I do a lot of low and slow bbq. Typically the smoker is at about 225 degrees F. So that kills most germs. The meat will usually be cooked to about 200 F. This is well above the safe cooking temp for beef chicken and pork.

The reason it is cooked slowly is to give the fats and connective tissues time to cook down into oil. Otherwise the meat will be tough and difficult to eat. If you toss ribs into a 500 degree oven and pull them out when they reach 165, they will be terrible. But letting them cook slowly for several hours until all of the fat, fascia, tendons, and ligaments break down into juicy oils is fantastic.