We often take for granted our amazing ability to experience food the way we do.
Think about it: a delicious salted caramel brownie would not be delicious if we weren't able to taste the sweetness, the saltiness and the slight bitterness from the rich cocoa. It would be moist and dense, but where would the flavour be?
*enters existential crisis*
The way we experience taste and flavour is unique, and it's not as simple as our taste buds doing all the work. And there's actually a big difference between 'taste' and 'flavour'.
"If we think of food, taste is only a part of it," Alex Russell, a taste and smell perception expert from Southern Cross University, told The Huffington Post Australia.
"A lot of the information we get from food is actually smell. This is why it's important to understand the difference between taste and flavour."
"A lot of people talk about taste in 'wine tasting', for example, but taste actually refers to specific sensations -- sweet, sour, bitter, salty are the original four and then umami was added and recognised properly around the year 2000," Russell explained.
"Sweetness is related to energy," Russell said. "Sweetness is sugar essentially, which is a short term energy burst, so that's why it's such a good thing. We like sweet things because we know that it gives us what we need to survive."
"In behavioural experiments we use sweet things as a reward. For example, if someone wants to train a rat in a maze to go a certain way, they give them a sweet drink. If they want to stop them from doing something, they will give them something bitter."
"Bitterness is something that's related to poison in general. We find things that are bitter aversive -- we don't want to eat them," Russell said.
"There are actually lotion and creams you can put on your nails if you bite your nails, and they're bitter. It's because bitter is something we usually don't like."
Although we often perceive bitter as bad, uncomfortable or poisonous, we can actually learn to like bitter things.
"Great examples there are things like coffee and beer. If you think of beer, the first time most people try beer it tastes gross, but you kind of get over it because you learn that beer also makes you drunk and have fun," Russell said.
"So, you get past this idea of bitterness and it gets to the point then when bitter becomes an essential component. Then, if you have a beer that doesn't taste bitter, it tastes weird, different and potentially wrong."
"Sour is about acids. If you think of hydrochloric acids, sourness is picking up the hydronium ions," Russell said.
"Again, it's generally fairly aversive but not as strong as bitterness. If you really want to stop someone from doing something, you would add bitterness to it rather than sourness."
"Saltiness is an easy one. If you think of table salt, that's the sodium ions we're detecting there. With saltiness, if you think of the periodic table, anything that's in that same family -- sodium, potassium, and so on -- if you get any of those ions (and they don't kill you) they will taste salty," Russell said.
"As with many of these things, too much can be aversive, as well. Even too much sweetness is wrong."
Umami is a kind of mysterious, unfamiliar word we wonder about when watching MasterChef, but the reality is that we experience umami on a daily basis.
Umami is a savoury, meaty and brothy taste -- think dried shiitake mushrooms, Vegemite, kombu seaweed, miso, parmesan cheese and MSG (yep, that tasty flavouring in chips, Asian soups and instant noodles is one of the simplest ways to add umami to food).
"We do have some understandings of umami. Umami is a word that is used to describe things like MSG, savoury, brothy, meaty. It's that sort of savoury taste," Russell said.
"If we think about taste, there are two types of tastes: sourness and saltiness are all about ions going through ion channels, whereas the other tastes (bitterness, sweetness and umami) work with G-protein-coupled receptors, so there are particular receptors that are sensitive to each type of taste."
Right now, you're probably imagining that neat primary school diagram of the tongue, portioned into areas which 'picks up' these five tastes. Get that map out of your mind. It's totally incorrect.
"No, that's absolute rubbish. It's one of those ones that's really stuck around for a long time," Russell explained. "There's a psychologist called Boring -- his name really is called Boring -- and it's my understanding that he mistranslated the original German text. So this idea came up that sweetness is on the tip of the tongue and so on, but it doesn't really make any sense."
According to the diagram, we experience bitterness (which is associated with poison) on the back of our tongue, which really isn't logical when we think about it.
"If that's the case, from an evolutionary perspective, why would bitter be the last thing that we taste before we swallow? Wouldn't bitter be on the front of the tongue?"
The sixth taste?
"There are other tastes that are starting to be recognised," Russell told HuffPost Australia. "There's a bunch of research coming out of Melbourne, which talks about fat as the sixth sense. We're not incredibly surprised by this, but certainly there's a fatty receptor that's been identified in rats."
The main tastes can also differ from person to person, and from culture to culture.
"It really depends on what you consider a taste to be. There are certain cultures that include other things as taste, like chilli which is pain," Russell said. "Certainly there's a whole bunch of tastes that people are trying to make the seventh and eighth tastes."
We often use 'taste' and 'flavour' interchangeably, but this is not correct. While taste refers to the five types above, it's only a part of how we experience a food.
"Let's say there's a piece of food going into our mouth. We might get a whiff of it on the way in, but once it goes into our mouths and we start chewing it up, it starts reacting with receptors not just on our tongue (we think it's on our taste buds), but they're also around the rest of our mouths. Your tongue is essentially picking up the sweet, sour, bitter, savoury and umami elements of the food," Russell said.
Flavour, however, is a 'hedonic' sense involving smell, texture, temperature and expectation. To put this into a real life situation, let's use strawberry ice cream.
"The actual taste of the strawberry ice cream would be sweet. It wouldn't really set off any other taste receptors in those primary tastes -- you're not going to think of strawberry ice cream as bitter," Russell said.
"But the actual strawberry-ness actually comes from smell. A lot of people don't understand this.
"It's not entering your nose via your nostrils at this point. It's entering your nose through your throat. If you've ever had a mouthful of liquid and someone made you laugh and it's come out of your nose, that's the passage that the odours are going through to get to your nose."
This perception of odours from our smell receptors via the throat is called retronasal olfaction. Orthonasal olfaction, on the other hand, is sniffing. Cool, huh?
"Flavour is the one where you've got all the elements going up into your nose, as well. So, you'll get the temperature of the ice cream in your mouth, that's the touch sensation. You'll get the sweetness, that is the actual taste itself. And you'll get the strawberry-ness from the smell through retronasal olfaction. Put all of those elements together and that's your flavour," Russell explained.
"We use the terms wrong all the time. We talk about 'wine tasting' but we should actually be talking about 'wine flavouring'. Though it's not as catchy."