Category: Food & Cooking

The holes in Swiss-style cheese are not tunnels left by mice and they are not drilled in at the factory.

They form during fermentation.

Certain bacteria used while making cheeses such as Emmental produce carbon dioxide gas as the cheese develops.

That gas becomes trapped in pockets.

The pockets become the holes.

Cheese is a controlled fermentation project

Cheesemaking begins with milk, but microbes and enzymes transform that milk into something very different.

Different styles use different bacterial cultures, temperatures, moisture levels, aging times, and handling methods.

Those choices affect flavor, texture, aroma, and appearance.

In Swiss-style cheeses, some of the bacteria continue producing gas during aging.

Where does the carbon dioxide come from?

Bacteria consume compounds available in the cheese and release metabolic byproducts.

One of those byproducts can be carbon dioxide.

The gas cannot always escape easily from the developing cheese.

Instead, it gathers in small spaces.

As more gas accumulates, the spaces grow.

Cheesemakers call these holes “eyes.”

Why are the holes round?

Gas presses outward in many directions.

In a soft, flexible cheese, that pressure tends to create rounded pockets.

As the cheese firms during aging, the shape becomes locked in place.

The result is the familiar smooth round holes.

Why are some holes large and others tiny?

The size and number of eyes depend on the bacteria, temperature, acidity, moisture, aging conditions, and other details of production.

Modern manufacturing can also produce Swiss-style cheeses with smaller holes than the giant cartoon version people often imagine.

There is no universal rule saying every slice must look like it lost a fight with a hole punch.

Do all cheeses make holes?

No.

Many cheeses use microbes and aging methods that produce little gas, allow gas to escape, or create completely different textures.

Some cheeses contain small irregular openings for reasons unrelated to the classic Swiss-cheese process.

The famous large eyes are a feature of certain styles, not a basic property of cheese.

Does more gas mean stronger flavor?

Not in a simple one-to-one way.

The same microbes and aging conditions that create gas also contribute to flavor development, but hole size alone is not a reliable flavor meter.

So mice did not tunnel through your sandwich.

Bacteria made gas.

The cheese trapped it.

Somehow the holes became the part everybody remembers.

A related bit of kitchen science appears in Why does bread rise?, where a different familiar food has its own chemistry.

And that’s the short explanation.

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Peppermint can make your mouth feel cold even when the mint itself has been sitting at room temperature.

The trick comes from menthol.

Menthol activates temperature-sensitive nerve receptors that normally respond when tissue cools.

Your brain receives a cooling signal even if the actual temperature changed very little.

Your nerves have temperature sensors

The body uses specialized proteins to detect potentially important temperature changes.

One of these is called TRPM8.

It responds to cool temperatures.

Menthol can also activate it.

That means the same signaling pathway can turn on because the tissue became colder or because menthol arrived.

Why does toothpaste feel cold?

Many toothpastes, gums, candies, and mouthwashes contain menthol or mint-derived flavor compounds.

When menthol reaches sensory nerves in the mouth, the cooling pathway becomes active.

The bathroom did not suddenly drop ten degrees.

Your nervous system changed its report.

Why does cold water feel extra cold after mint?

The receptor is already being stimulated by menthol.

Then genuinely cold water adds a real temperature change on top of the chemical signal.

The combination can make the cooling sensation feel especially strong.

This is why a sip of ice water after strong mint can feel almost aggressively cold.

Is mint lowering the temperature at all?

Sometimes evaporation and airflow can produce small real cooling effects, but the characteristic mint sensation does not require a dramatic temperature drop.

Menthol can create the feeling even in otherwise warm surroundings.

Is menthol the opposite of capsaicin?

In a useful everyday sense, they pull opposite sensory tricks.

Capsaicin activates pathways associated with heat and burning.

Menthol activates a pathway associated with cooling.

Neither chemical needs to change the temperature enough to match the sensation.

Your nerves are reporting how their receptors were activated, not reading a thermometer.

Why does mint feel refreshing?

Humans generally associate cool sensations with freshness and relief from heat.

That makes the menthol effect useful in foods and personal-care products.

The chemical signal becomes part of the flavor experience.

So peppermint is not carrying a little air conditioner around inside the leaf.

It is convincing your nerves that somebody turned the thermostat down.

A related bit of kitchen science appears in Why do chili peppers feel hot?, where a different familiar food has its own chemistry.

And that’s the short explanation.

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A chili pepper can make your mouth feel as though the temperature suddenly jumped.

Usually it did not.

The sensation comes largely from a chemical called capsaicin.

Capsaicin activates sensory receptors that normally help warn you about actual heat and physical irritation.

Your brain gets the message and responds accordingly.

Capsaicin activates heat-sensitive receptors

Nerve endings in the mouth and skin contain a receptor often called TRPV1.

This receptor responds to potentially damaging heat and some irritating chemicals.

Capsaicin fits into the system and activates it.

The nerve sends a signal associated with heat and burning.

Your brain does not receive a little footnote saying, “Do not worry, this is only salsa.”

It receives the alarm.

Is spicy food actually burning your mouth?

Not in the ordinary thermal sense.

A room-temperature pepper can produce an intense burning sensation without raising the tissue temperature to the level that caused the sensation.

Very high concentrations of capsaicin can irritate tissue, but the familiar “hot” feeling from food is mostly sensory signaling.

Why do you sweat when you eat spicy food?

Once the brain interprets the signal as heat, it can activate responses normally used during overheating.

You may sweat.

Your face can flush.

Your nose can run.

Your eyes may water.

The body is reacting to a heat message even though the pepper did not turn the inside of your mouth into an oven.

Why does water not help much?

Capsaicin does not mix especially well with water.

A drink of water may briefly move the sensation around without removing much of the capsaicin from the tissues.

That is why water can feel disappointingly useless after a very hot bite.

Why can milk work better?

Fat and milk proteins can help loosen and carry capsaicin away from receptors more effectively than plain water.

The exact relief depends on the food and the person, but dairy products often work better than water for this reason.

Why do people enjoy something that hurts?

The burning sensation can be unpleasant, but spicy food also comes with flavor, aroma, cultural habits, expectation, and sometimes a rush of physiological arousal.

People differ enormously in how much capsaicin they enjoy and tolerate.

Repeated exposure can also make the experience more familiar.

So spicy food is not really setting your mouth on fire.

It is pressing the fire-alarm button.

Some people apparently enjoy dinner with the alarm going off.

A related bit of kitchen science appears in Why does your nose run when you cry?, where a different familiar food has its own chemistry.

And that’s the short explanation.

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Bananas turn brown because they keep ripening after they are picked.

The peel changes from green to yellow and eventually develops brown spots as pigments break down, cell structure changes, and chemical reactions continue in the fruit.

The banana you brought home is very much still doing things.

Ethylene helps control ripening

Bananas are climacteric fruits, which means ripening is strongly influenced by the plant hormone ethylene.

As a banana responds to ethylene, several changes happen at once. Starches in the fruit are converted into simpler sugars, which is why a ripe banana tastes sweeter than a green one.

The fruit softens as structural materials in its cell walls change.

Aroma compounds develop too.

That familiar banana smell is part of the same ripening process.

Why does the peel change from green to yellow?

Green banana peels contain chlorophyll.

During ripening, chlorophyll breaks down and other pigments become visible, producing the yellow color we associate with a ripe banana.

Continue the process and the yellow does not remain permanent. Pigments and cells keep changing, and brown areas begin appearing.

Where do the brown spots come from?

Several processes contribute to browning.

As peel cells age or become damaged, enzymes can interact with compounds that were previously separated inside the cells. In the presence of oxygen, these reactions can produce brown pigments.

Bruising speeds the process because physical damage breaks cell structures and gives enzymes and oxygen easier access to one another.

That is why a banana can develop a dark patch exactly where it was squeezed in a grocery bag.

The banana remembers poor luggage handling.

Does brown mean the banana is rotten?

Not necessarily.

Brown spots often indicate a very ripe banana. Inside, the fruit may be softer, sweeter, and more aromatic than it was a day or two earlier.

That makes heavily spotted bananas useful for baking, smoothies, and other recipes where sweetness and soft texture are advantages.

Spoilage is a separate issue. Mold, leaking fluid, a fermented or unpleasant odor, or badly deteriorated flesh can indicate that the fruit has moved beyond ordinary ripening.

Color alone does not tell the whole story.

Why do bananas make other fruit ripen faster?

Bananas produce ethylene and can expose nearby fruit to it.

Other ethylene-sensitive fruits may therefore ripen faster when stored close to bananas, especially in a closed bag or container where the gas accumulates.

This can be useful if you are trying to ripen an avocado or pear.

It is less useful when everything in the fruit bowl appears to have scheduled retirement for the same Tuesday.

Does putting bananas in the refrigerator stop browning?

Cold temperatures slow many ripening reactions, but bananas are tropical fruits and their peels are sensitive to chilling.

A ripe banana placed in the refrigerator may develop a dark peel quickly even while the fruit inside remains usable for longer.

Very green bananas are generally better allowed to ripen at room temperature first.

Why does separating bananas sometimes help?

Ethylene concentration and air circulation can affect ripening. Separating fruit or improving ventilation may modestly slow the way ethylene accumulates around the bunch.

It will not stop ripening indefinitely.

The banana is still on the clock.

So brown spots are not an instant spoilage alarm.

They are often the visible sign that the fruit is moving through the final stages of ripeness.

At some point the scientific question becomes less “Why is it brown?” and more “Do we own a banana bread pan?”

A related bit of kitchen science appears in Why do apples turn brown?, where a different familiar food has its own chemistry.

And that’s the short explanation.

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Soda fizzes because carbon dioxide gas has been dissolved in the liquid under pressure.

While the bottle or can is sealed, the high pressure above the drink helps keep a large amount of carbon dioxide dissolved in it.

Open the container, and the situation changes immediately.

Pressure keeps more carbon dioxide dissolved

Gases can dissolve in liquids. How much stays dissolved depends on factors including pressure and temperature.

During carbonation, manufacturers put carbon dioxide into the drink under elevated pressure. The sealed container helps maintain that condition.

When you open it, the pressure above the liquid suddenly falls toward ordinary atmospheric pressure.

The drink can no longer hold as much carbon dioxide in solution, so gas begins escaping.

That escaping gas is the fizz.

Why do bubbles start on scratches and surfaces?

A bubble needs somewhere to begin.

Tiny scratches on a glass, fibers on a straw, bits of ice, sugar crystals, or other rough surfaces can provide nucleation sites where carbon dioxide molecules gather.

Once a small gas pocket forms, more carbon dioxide can enter it. The bubble grows, rises through the drink, and releases its gas at the surface.

That is why bubbles often seem to stream from particular spots on the inside of a glass.

The glass has tiny launch pads.

Why does shaking soda make such a mess?

Shaking creates many small gas pockets and mixes gas throughout the liquid.

Open the container immediately afterward, and the pressure drops while all those potential bubbles are ready to grow.

Carbon dioxide expands and escapes rapidly, pushing liquid along with it.

The soda did not become more carbonated because you shook it. You simply created a much better escape plan for the gas already there.

Why does warm soda foam more easily?

Carbon dioxide is generally less soluble in warmer liquid than in colder liquid.

That is one reason cold soda tends to hold carbonation better. Warm a carbonated drink, and the gas is more eager to leave the solution.

Temperature and pressure work together, which is why a warm, shaken can is not an experiment you need to repeat for science.

Why does soda eventually go flat?

Once the container is open, carbon dioxide keeps moving out of the drink until the system approaches a new equilibrium with the surrounding air.

Every bubble that escapes carries away some carbonation.

Resealing a bottle slows the loss because pressure can build again in the headspace, but it does not perfectly restore the original factory conditions.

Leave the drink open long enough and most of the extra dissolved gas leaves.

The result is flat soda.

Does the carbon dioxide affect anything besides bubbles?

Yes. Some dissolved carbon dioxide reacts with water to form carbonic acid, which contributes a little to the tart character of carbonated drinks.

Many sodas contain other acids too, so carbonation is only part of the flavor chemistry.

But the visible show is straightforward.

Carbon dioxide is packed into the drink under pressure.

You open the container.

The pressure drops.

The gas leaves with bubbles, noise, and occasionally your dignity if you shook the can first.

A related bit of kitchen science appears in What is pH?, where a different familiar food has its own chemistry.

And that’s the short explanation.

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A popcorn kernel is a remarkably well-designed little pressure vessel.

Inside the hard outer shell are starch and a small amount of water. Heat the kernel, and that water becomes the key to the entire transformation.

A popcorn kernel traps water inside

Popcorn is a particular type of corn with a hard, relatively moisture-tight outer layer called the pericarp, often simply called the hull.

The inside contains starchy endosperm and water. Proper popping depends on the kernel retaining enough moisture after harvest and storage.

When the kernel is heated, the water gets hotter and eventually produces high-pressure water vapor inside the sealed hull.

The steam cannot simply drift away because the outer layer is tough.

Pressure builds.

Heat also softens the starch

While the pressure rises, the starch inside the kernel becomes hot and soft.

Eventually the hull can no longer contain the pressure. It ruptures suddenly.

The pressure inside the kernel drops almost instantly, allowing the superheated water to expand into steam. The softened starch expands outward with it.

The kernel essentially turns itself inside out.

As the expanded starch cools, it solidifies into the light, crunchy structure we call popcorn.

That is a fairly dramatic career change for a grain of corn.

Why does popcorn jump when it pops?

The rupture is not perfectly symmetrical. As the hull breaks and the starchy material begins expanding, the forces can push against the surface beneath the kernel and launch it into the air.

High-speed studies of popping kernels have shown that the opening and expansion can act a little like a tiny leg pushing the kernel upward.

So the jumping is part of the same rapid mechanical event that creates the puff.

Why do some kernels never pop?

Unpopped kernels often have a moisture problem or a damaged hull.

If the outer shell is cracked, steam can leak out before pressure becomes high enough to rupture the kernel explosively.

If the kernel has dried too much, there may not be enough internal water to create the necessary pressure and expansion.

That is why popcorn is stored so that it does not become excessively dry.

The sad hard kernels at the bottom of the bowl are not necessarily defective corn. Some simply failed the pressure test.

Why does ordinary sweet corn not pop the same way?

Different types of corn have different hulls and internal structures. Popcorn has the particular combination of a strong outer layer and suitable starchy interior needed to trap pressure and expand dramatically.

Other corn varieties may split or crack when heated, but they generally do not produce the same fluffy result.

Does microwave popcorn pop differently?

The basic physics is the same whether popcorn is heated in a pan, hot-air popper, or microwave bag.

The method changes how energy reaches the kernel. The kernel still needs internal water, a strong hull, heat, and enough pressure to burst.

So popcorn is not exploding because the microwave has a special “popcorn frequency.”

The kernel already contains the equipment.

The heat simply starts the countdown.

A related bit of kitchen science appears in Why do onions make you cry?, where a different familiar food has its own chemistry.

And that’s the short explanation.

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Organic milk often seems to have a much later expiration date than conventional milk. The main reason is usually not that organic milk is naturally slower to spoil.

It is processing.

Many organic milk products in the United States are ultra-pasteurized, which means they are heated to a higher temperature than milk treated with standard pasteurization.

Regular pasteurization already kills harmful microbes

Milk is pasteurized to reduce disease-causing organisms and make the product safer.

A common U.S. method is high-temperature, short-time pasteurization. The milk is heated to at least about 161 degrees Fahrenheit for at least 15 seconds, then cooled.

That greatly reduces harmful bacteria and many spoilage organisms.

But it does not sterilize the milk.

Ultra-pasteurization uses more heat

Ultra-pasteurized milk is heated to about 280 degrees Fahrenheit for at least a couple of seconds.

That much higher temperature destroys more microorganisms and inactivates more enzymes that could contribute to deterioration.

The result can remain unopened in the refrigerator considerably longer than conventionally pasteurized milk.

Some milk treated with ultra-high-temperature processing and packaged aseptically can even be shelf-stable before opening.

Why is organic milk often ultra-pasteurized?

Distribution is a big reason.

Organic milk represents a smaller share of the market and may travel farther from processor to store. A longer unopened shelf life gives producers and retailers more time to transport and sell it.

Ultra-pasteurization reduces the chance that the product will spoil before somebody buys it.

Conventional milk can also be ultra-pasteurized. Organic milk does not own the technology.

Does “organic” itself preserve milk?

No.

Organic standards describe how the cows are raised and how the farm is managed. Those rules do not create a natural preservative inside the milk.

If two milks received the same processing and were handled under the same conditions, the organic label by itself would not explain a dramatic shelf-life difference.

The processing method matters far more.

Does ultra-pasteurization change the taste?

Some people notice a slightly different flavor because high heat can alter some milk proteins and produce subtle cooked notes.

Others barely notice a difference.

Nutritionally, both conventional and organic milk can provide protein, calcium, and other nutrients. The shelf-life question and the nutrition question are separate.

What happens after you open it?

The long date on the carton applies mainly while the package remains unopened and properly refrigerated.

Once you open the container, microbes from the air, the refrigerator, hands, and pouring surfaces can enter. The clock changes.

Follow the package instructions and use smell, appearance, storage history, and the manufacturer’s guidance rather than assuming the distant printed date still guarantees freshness after opening.

Why is some UHT milk sold unrefrigerated?

If milk receives UHT treatment and is filled into a sterile package under aseptic conditions, it can remain shelf-stable until opened.

That is common in many countries.

The carton does not contain a different species of milk. It is a different combination of heat treatment and packaging.

So when organic milk appears almost suspiciously immortal compared with the jug beside it, the answer is usually straightforward.

The cow did not perform a miracle.

The processing plant did.

A related bit of kitchen science appears in Why do onions make you cry?, where a different familiar food has its own chemistry.

And that’s the short explanation.

Related explanations: Why do onions make you cry? and Why does popcorn pop?