Pizza doesn’t last long around me! Seriously,
though, there are several factors that influence
how quickly food “goes bad.”
What actually makes food go to the dark side is
that bacteria and fungi (like mold) start to
grow on the food. If you put a slice in an
airtight container, then heated it up so high that
nothing could live in it, it would never rot or
get moldy. This is how canned foods work. Unless
the can is damaged or develops holes, canned foods
are safe for a long time. They may lose some
flavor and get all mushy, but nothing will grow on
them. (I still don’t recommend eating canned goods
older than you are because the plastic or metal in
the can might seep into the food after a while. )
This is a good time to mention that when
food has already started to go bad, heating won’t
make it good again. The bacteria and mold will
die if the temperature is high enough, but if they
have made toxins (like botulism toxin),
those toxins will still be there.
You’re probably not going to can pizza, so let’s
look at the factors that make food go bad faster.
They’re basically the things that bacteria and
fungi need to live. They generally like to live
in warm, moist places. Long before
refrigeration, people would dry foods like
vegetables, meat and fruit to keep them from
spoiling. That’s because living things need
water to grow. The trick is to get the drying
to happen fast enough so that the bad stuff can’t
So before there were food driers, people would
cut things very thin, then hang them in the hot
sun, preferably when it was windy. Using smoke
protects meat from bad stuff, including flies that
might be looking for meat to lay their eggs on.
You can also dry things when it’s below freezing.
It takes longer, but there won’t be any bugs
around, and the bacteria and fungi can’t grow in
the cold. Adding a lot of salt or sugar also helps
preserve food because the salt or sugar draw water
out of cells through a process called
osmosis. It’s another type of drying.
Let’s get back to your pizza. The environment is
important; cold and dry keeps food safe
longer. If you want it to last a long time,
put it in the freezer. If you want to eat it
later, you’d better put it in something air-tight
so that it won’t dry out. It will keep pretty much
forever, but will start to taste bad and lose its
texture as it dries out. This is called
“freezer burn.” This is a good time to
mention that when food has already started to
go bad, freezing won’t make it good again.
The bacteria and mold won’t die, they’ll just go
into a sort of suspended animation. When you thaw
the food, they get right back to work. If they
have made toxins, those will still be there.
Putting food in the refrigerator buys you more
time than leaving it on the counter because the
metabolism (a fancy name for the chemical
reactions) of the bacteria and mold will slow down
in the cold. This slows down their growth.
Refrigerators also dry food out, which is bad for
the bad stuff, but won’t help with flavor or
texture. The sooner you get food into the cold,
dry environment, the better.
The nasty stuff grows fast, so you want to get
it cold fast before the population of the bad
stuff gets too big. I saw a site that said the
pizza is good for about 3-4 days in the
refrigerator, but you can’t leave it on the
counter overnight, then expect it to last 4 days
in the fridge.
The type of food makes a difference too. Most of
the nasty stuff grows best at a neutral pH.
Pickling was invented to preserve foods by making
their environment acidic. People also recruit good
bacteria to make environments acidic. Yogurt and
cheese rely on friendly bacteria. Mold and
bacteria love a little sugar. Pizza sauce is wet
and has some sugar in it, so they’ll probably go
after that first. Pineapple is probably another
big target. Mold loves cheese. Bread gets moldy
fast, but the pizza crust is so dry that it will
probably go bad later than the other stuff. Olives
and anchovies will take longer because they’re
salty. Smoked meats will last longer than
hamburger. Another factor is whether the food
contains preservatives, which slow down spoilage.
The bottom line is, don’t take chances with food
poisoning. Keep hot foods hot and cold foods
cold. When hot food starts to cool down, put it in
the cold. Keep things clean, too. Remember,
tossing the food is better than “tossing your
The science of making mummies is basically about
preservation of meat. What conditions do you think
make mummies possible?
Thanks for asking,
The answer largely depends on the conditions in
which the pizza is being stored. Perhaps you left
the pizza on the kitchen counter over night. At
room temperature, bacteria that cause food-borne
illness can contaminate the pizza. These
bacteria grow best between 40-140 degrees
Fahrenheit, known as the danger zone. According
to the US Department of Agriculture, any
perishable food (including pizza) is not safe to
eat after sitting for more than a few hours at
However, maybe you put the pizza in the
refrigerator before going to bed. Refrigerators
keep food below 40 degrees Fahrenheit, and thus
can preserve food for longer by slowing down
bacteria growth. Generally, pizza can be kept
in the fridge for ~4 days and be ok to eat.
You could even store your pizza in the freezer. In
an airtight container in the freezer, below 32
degrees Fahrenheit, a pizza could last 1-2 months.
The pizza would probably be safe to eat after even
a longer time, but the freshness and quality will
decrease with time in the freezer. In
principle, if you kept your pizza cold enough, for
example cryogenic freezing with liquid nitrogen,
the pizza could last indefinitely long.
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