Why can't we taste food when our nose is blocked?

Flavor = Taste + SmellWhat we call "Flavor" is a combination of taste and smell.There are only five taste: salty sweet, sour, bitter and savory/umami.  Compared to taste, there are virtually unlimited number of scents humans can detect. So how many? It's one trillion according to The Science magazine: http://www.sciencemag.org/news/2014/03/human-nose-can-detect-trillion-smellsTherefore, when your nose is blocked, basically you can only "taste" the food and unable to "smell", missing the majority of your food's flavor. This is the reason why you were unable to taste anything when you had a cold.

Most of what we taste in our food is actually smell. We can only taste sweet, sour, salt, bitter, and umami (a savory sensation of meatiness). Anything else we only think we're tasting -- we're really smelling our food and enjoying the mixture of smell and the basic taste. So when your nose is clogged, you can't inhale the aroma, and your food is reduced to the 5 basic tastes your tongue and mouth can give you.

Because of your olphactory bulb being blocked. This is the series of nerve endings in your nose, that not only allows you to smell, but to taste at the same time. If your nose is clogged, and swollen with mucus, you have a tough time smelling things, and in turn...tasting things.

As a avid home brewer and bar owner I used to host beer and single malt  tastings, and I learned a lot about how our perception of taste is shaped.   For instance, why drink beer from a clear glass rather than a can, or brown bottle?  Two reasons, seeing the beer or other food, lets your vision shape your perception before your other senses come into play.  The color of the food or beer prepares you for what you think it will taste like.   Is it green?  Do you anticipate lime? or something like broccoli or peas? Is it yellow or orange?  You might anticipate yet more citrus. Red...hot or berry?   Is the beverage clear or murky?  Is the food nicely presented or does it look like something you stepped in and scraped off your shoe?   Try a blind taste test, that is actually blindfold yourself to see how sight changes your perception of taste.   Then your nose comes into play.  You smell the beverage or food and it gives you more information to shape the taste sensation.  Your nose fills with the aroma that sets the stage for actually tasting the food or beverage.   That tells you a lot based on prior experience.   When you sinus are filled you miss a third or quarter of the tasting experience.   Next you feel texture before you actually taste.  To get a full encompassing taste sensation, with beer, wine or spirits, you have to chew it.  Yes, chew the beer and let it coat your whole tongue.  Does it feel thick or thin on your tongue?   As a good example of how texture affects taste, I need not go any farther than Sushi.  Most people who have never eaten it, have a hard time getting past the sensation on their tongue.  It looks pretty, it smells good, but the texture of raw fish is off putting.  The rice, no problem.  The difficulty starts when the nari and the fish hit your tongue.  Nari is dried seaweed it instantly hydrates and kind of sticks to your teeth.  Then the fish, depending on its freshness, can be a bit on the slimy side.  DO NOT, repeat DO NOT ever try sushi for the first time at your local grocery store sushi grab and go section.  You have no clue of the quality or age of the fish nor how long your plastic wrapped tray has been sitting there in the cooler.   So texture plays a big part in taste.  Again, close your eyes and eat something that someone gives you and see how much your perception changes if you don not smell or see it first.   Now American beer makers, oh, excuse me, Anheiser Bush is owned by AB Inbev a Brazilian mega combine, they also own Stella and Corona and a bunch of Euro brands too.  They are changing recipes and delivery vehicles for beer, so taste your beer often as it may be changing on you.  Like Beechwood aging?  Well maybe not so much in the future since they changed suppliers and the Busch family's supplier went belly up as a result.  Its all cheaper, faster and less expensive for the new owners.   I digress, chewing coats you whole tongue.  Not chewing  your beer, and drinking from a longneck or can, just pours the ice cold, tongue numbing liquid down your throat.  Yes it quenching but also flavorless as virtually none of the beer touched a taste bud and those that did get a splash of beer went numb since they tell you to drink it ice cold.  Ever let an American non-craft brew warm up?  Yes, it tastes like something out of the garden hose.   So, a whole new world of beer just opened up, if you chew it, and drink it at the temperature it was made for, not 32F but a bit warmer, maybe in the 40's or even 50F range, it will rock your world of flavor.   The same goes for food.  Chew it, let your taste buds do their thing.  They cannot if you wolf your food.   Wolfing your food. Interesting phrase.  Ever read Jack London about is time spent in the Yukon?  Wolves will gobble down just about anything without tasting it.   So they used to take a hunk of meat, whale or seal, and shove a length of sharpened flexible baleen into it.  Its the thin stuff used for corset stays that acts as a filter in some whales mouths.  Then they would bend the meat along with the springy bone inside it double, tie it and throw it outside to freeze.  Then they would remove the string and throw the meat out where the wolves could get it and wolf it down the nice compact hunk of meat.   Once the meat defrosted in the wolves belly, Boing! the springy bone would straighten out and pierce their intestines condemning them to a long protracted death by peritonitis.  Makes using cyanide or strychnine almost humane.   So the lesson is do not wolf your food.  Chew it, enjoy it.  Masticate, Masticate.  Chew and chew some more for sold food. Beverages only need a few chomps and swirl to coat your tongue.  It aids in digestion, and you will taste more of the food and drink that you consume.

As others have already written, our senses of smell and taste work together to bring the whole experience together. When you can't smell, you can still taste, but what you are used to describing as 'taste' is actually the combined senses from your nose and tongue and other parts of your mouth. A famous experiment with smell and taste has blindfolded, nose blocked testers taste apples and onions and are unable to tell the difference. Without the sense of smell, you are not getting the whole flavour profile you are used to experiencing. Complete and permanent loss of the sense of smell (anosmia) is a very serious condition, not only because you are unable to smell off odours and smoke (just two examples) but because if you are no longer getting the full flavour profile you often lose interest in food, because it isn't as enjoyable.

Your taste is not much affected but it was not much to start with. Most of the sensations about food are coming from other organs namely  eyes and nose. Our eyes are scanning the food and communicate with memory: what was the food corresponding to that shape, was it pleasant? So often, kids do not want to eat something then finally after we force them to taste, they like it because the taste was not what their eyes were telling them. Nose is giving even more prononced sensations, we can smell thousands of different substances and those sensations are added on top of the taste and the images, they will be recorded in the brain as a pleasnt or unpleasant experience. When your nose is blocked, that sense is blocked and you are left with tasting which is not much in humans. Our brains is now questionning itself about the past experiences on the same food because the correspondance is simply not there.

It is said that the taste of food changes when you cannot smell them because the olfactory organs are blocked and not activated. This is in spite of the taste receptor cells being unaffected.

We taste with our sense of smell as much as we do our tongue. Our tongue and taste buds really only recognize sweet, salty, sour, and more broad flavor components, while our sense of smell is what tells our brain what we're tasting and eating. This is why you nose a glass of wine or scotch, this is why we take a whiff of food before we eat it, why our mouth tastes sour just from smelling sour candies. When kids don't want to taste nasty cough syrup, that's why they clamp their nose. When people ask the age-old hypothetical of which sense they'd be willing to give up, some people say smell not realizing they'd really be giving up taste too.

Actually, you can taste food with your nose blocked, just not as well.  You have several areas of taste buds on your tongue, sweet, salty, bitter, and sour.  But you taste with your eyes (looking at a food and imagining how it will taste based on other similar looking foods you ate in the past) as well as you nose (a particular food smells like something you ate before, so your brain perceives it to be similar).  Without seeing and smelling, an apple and an onion 'taste' about the same, and mostly because the shape, weight, and texture are so similar.  However, if you really try to taste without seeing or smelling, an apple tastes slightly sweeter than most any onion, and the onion will have a slightly more bitter taste than an apple.  So, you do taste things when you have your nose blocked, but the expected aromas accompanying the food are not there.  That is why you think you can't taste, but in reality you can't smell.