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How to taste wine - Perceiving Wine

When people are assessing wine, there are three senses to focus in on - how it looks, smells and tastes. In this series we look at the science of wine tasting and how the wine creates the perceptions we enjoy. In part one we look at the wine with our eyes to see what we can learn. For a general overview of tasting wine see wine tasting.

The three parts are

The colour of wine

Our eyes can pick up a range of colours in the wine, but it is not just the colour we can get from the wine, we can learn about the age, condition and style of the wine. In blind tasting this can be very useful to give you clues about grape variety and winemaking style.

Usually we divide the wine world into three easy colours - white, rosé and red. While this is a good first attempt the colour of the wines rarely matches this general guide. I have never seen a milk white wine. Rosé is technically 2/3 red 1/3 blue and is quite a garish pink colour, while most young red wine has a blue to purple tinge! Let's start with white wine.

White Wine

Obviously it isn’t white and often comes from green or yellow grapes although red grape varieties can produce white wine. So what is meant? Normally most wine experts would describe white ranging between lemon-green, lemon, gold, amber, brown, even the clearest looking wine will have a faint tinge to it.

A young white wine will often be quite clear with a tinge of lemon or green lemon. As the wine ages it becomes golden in colour. Straw yellow is a common shade of wines with moderate age, while gold is the characteristic of good wines in their mature state. In addition a wine can turn golden by placing the wine in an oak barrel. The wine picks up the colour from the wood, in the same way clear whisky turns golden brown from exposure to oak barrels.

Rosé Wine

In rosé and red wines, colour leaches from the skins of the grapes to the juice, changing the colour of the juice. Rosé is the classic shade for wines with short skin contact. Leave the wine in contact with the grape skins slightly longer and the wine can develop a deeper strawberry colour. Wines made from very dark skinned grapes can show a salmon colour. Dark-skinned varieties with short skin contact can have an orange colour. A browning to onion skin can show either an ageing or maturing wine or oxidation.

Red Wines

Many red wines, but not all young red wines, often have a very blue/purple colour to them. As the wine ages the blue fades leaving the wine quite red in colour, as the wine oxidises it takes on a brownish colour. But by the time the wines is brown it is getting very old and is likely to be oxidised but also most likely well past its best. Even tawny wines (apart from port) are likely to be near the end of their life but possibly still drinkable.

But what control the colour in the wine? The colour in wines comes from three categories. First are the anthocyanins. This is the colour that comes from the grapes and usually the skins. They leach out when the skins are left in contact with the juice. Anthocyanins are very reactive and not stable; they react with both sulphur dioxide and oxygen and bleach, that is, they turn clear.

During fermentation the anthocyanins react with yeast derived by products and polyphenolics of which tannins are the most common, this creates more stable pigmented polymers. These are very important in forming stable colours in wine.

The third group of colours are known as anthocyanin-derived pigments which arise from the reactions between anthocyanins and other phenolic and aldehydes. These are still quite reactive and can from further combinations with tannins to form pigmented polymers.

In young wines the density colour is based on two factors - the amount of skin contact the wine has had and the level of sulphur dioxide in the wine. Most of the anthocyanin in red grapes is in the skin, so leaving the grapes in contact with the skin for long peropds of time helps leach the colour from the skin into the wine. The second key factor is the level of sulphur dioxide in the wine, Sulphur dioxide bleaches the wine, so high levels will create a lighter coloured wine. The acidity (or more accurately, the pH) in the wine can also influence the colour although this is not as pronounced as skin contact and sulphur dioxide.

In young red wine, anthocyanins occur predominantly as a dynamic equilibrium in five major states. One bonded to sulphur dioxide and four free forms. Most forms are colourless within the pH found in wine. Red wine colour comes primarily from the small proportion of anthocyanin that exists in a state known as flavylium. The proportion in this state depends upon the pH and free sulphur dioxide in the wine. Low pH (i.e. high acidity) increases the concentration in the flavylium state enhancing the red colour. As the pH rises the colour density and proportion of anthocyanin in the flavylium state decreases rapidly. Another state of anthocyanin is quinoidal and this is responsible for the blue colours in wines that have a high pH

Anthocyanins readily react with tannins and other polypehnols to form long chains of molecules. This polymerisation or connecting up to form chains is similar to the effect that tannins undergo making larger tannin molecules that taste softer, rounded and less harsh. But for wine, the making of longer chains is important to stabilize a wine's colour by protecting the anthocyanin from oxidation. Polymerization makes anthocyanins more resistant to bleaching from sulphur dioxide and high pH. In addition anthocyanin are more coloured when connected to tannins. Polymerisation increases the proportion of both flavylium (red) and quinodial (blue) states. However polymeristaiton and oxidation change the colour of red wines to yellow brown. Combined with the loss in red and blue colours the yellow-brown flavylium and quinodial anthocyanin-tannin polymers result in the wine progressively taking on a brickish red shade and eventually moving to tawny and finally brown.

Part 2 The taste of wine

The need to taste is most likely a genetic trait to ensure we eat foods that are good for us and don't poison us. So, while it may sound strange, most of the flavours we taste in our mouths are not coming from our mouths, but from our nose. Flavours travel through the back of our mouth up into our nose. Our mouths only taste a limited number of sensations.

Not everybody tastes the same and different cultures have different descriptions for what they taste. The key effects for wine and generally undisputed are salt, sweet, sour, and bitterness. Where sour in wine refers to acidity and bitterness is associated with tannins. Japan includes umami and kokum where umami is meatiness or savouriness and kokum is a richness or weight, in wine caused by alcohol. Not often covered by different cultures is a metallic taste in your mouth often associated with the taste of blood. Some scientist have even found that mice, and possibly humans, have receptors for fatty acids and calcium.

But what are these receptors? Taste receptors work by a chemical reaction causing nerve impulses to go to the brain. But how that impulse is created varies.

Salt and sour are detected by the presence of ions that interact with proteins in what is called the ion channels. These control the voltage across the cell's membrane which eventually forms a signal. Salt uses sodium ions while sour uses hydronium ions (H3O+ ions) that are formed from acids and water.

Sweet, umami (pronounced oo-mom'-ee) and bitterness use a series of receptors called G proteins-coupled receptors. These are a grouping of proteins that sense molecules outside the cell and activate signals inside. The human genome encodes roughly 350 G protein-coupled receptors, which detect hormones, growth factors and taste. Approximately 150 of the GPCRs found in the human genome have unknown functions so there could easily be other taste sensations we are not aware of. For example in western cultures umami is not considered a taste, but in Japan, umami (savoury) is the taste of meatiness, and is triggered by amino acids, found in protein-rich foods such as meat, cheese and fish. In wines it is associated from the autolysis (breakdown) of yeast, so is most likely to be present in sparkling wines that have been aged on the lees for 5+ years and Fino sherries that have been aged under the flor. Salt, particularly, highlights umami, which may explain why salty foods go so well with Champagne and Fino sherry with salty, roasted almonds is fantastic.

Another receptor in the mouth is called the CD36 receptor, it is the Fat receptor, or more importantly fatty acids, such as omega 3. It is important as it works to trigger gastric juices to digest the fats. But more work is required to determine if there is a taste relationship between fats and taste.

The sensation of temperature is very important to wines. Many wines are hot, that is they have a hot spicy character to them. In wine it is caused by the alcohol, but the reaction is the same to a high temperature dish or a hot spicy chilli. Hot is not technically a taste, because the signal is carried to the brain by a different set of nerves (trigeminal nerve), which also gives information about other parts of the body such as the nasal cavity, under the fingernails, or a wound. But the pain/temperture sensors (known as polymodal nociceptors) do give a physical reaction to the alcohol in wine.

Given that taste is based on chemical reactions you would think that the taste of salt or sour does not change. In fact this is not the case. In recent work by Barry Green on Thermal Taste, or how tastes change with temperature, Barry has shown for example individuals sensitive to salt will notice that an ice cube touched to the very tip of the tongue for a few seconds will begin to taste salty. Unfortunately Thermal taste probably does not affect the taste of most foods and beverages because the temperature conditions that produce it are rarely encountered during eating or drinking.

Another interesting example of our tastes becoming confused is eating the Miracle berries or miracle fruit. This berry once chewed converts the taste of sour to sweet. Eating a small part of the berry makes lime juice to rich and very sweet. The effects last between 30 minutes and 2 hours. While the exact cause for this change is unknown, one hypothesis is that the effect may be caused if miraculin works by distorting the shape of sweetness receptors "so that they become responsive to acids, instead of sugar and other sweet things".

Part 3 What type of taster are you

The taste test advocated by American MW and chef Tim Hani and adopted by Morrisons, is a revolutionary way of trying to give scientific rigour to why people like or dislike certain wines. The concept behind it is very simple. We all taste differently but some have more taste than others, literally. In the past most scientists have classified a person's taste as "Super Taster" "Normal" and "Non Taster".

Generally "Super Tasters" have the following attributes:-
• Fussy eater
• Do not like Bitter foods and drinks such as
• Tannic red wines
• Black coffee
• Dark chocolate
• They often have a sweet tooth
• They often have higher salt diets
• Alcohol tastes bitter
• They don't like sugar substitutes which taste artificial and bitter.
"Non Tasters" • Tend to like most foods

Testing for Super tasters

There are 3 methods of testing for Super Tasters PROP, blue tongue and the taste test. The best method is to count the number of fungiform papillae. These are tiny mushroom shaped projections on the tongue. They are scattered throughout the tongue but mainly at the tip and sides. Within them they house your taste which can distinguish the five tastes: sweet, sour, bitter, salty, and umami. If a person has less than 15 in a standard hole punch they are considered a Non-taster. Over 30 and you are considered a Super Taster.

A more error prone method is to give people propylthiouracil ( or PROP). This is a chemical that causes supertasters to have a strong bitter taste reaction, and is not very pleasant. Normal Tasters can taste it but not as intensely while Non Tasters tend not to notice it. The problem is calibrating a reaction to it. Many people are simply given a piece of paper with it impregnated in it, with Normal and Super Tasters it is difficult to know who has reacted the most. More accurate tests involve first calibrating the precipitant with a salt.

The final way is the taste test. It is the least accurate but the simplest to implement. Users are asked how they drink coffee, their reaction to diet drinks and salt.

How do you take your coffee?
1. I don't like Coffee
2. Cappuccino with sugar
3. Latte
4. Strong white coffee
5. Black coffee

Do you like Sweeteners?
1. They taste bitter
2. They taste too sweet
3. I don't notice them
4. They taste okay
5. They're great

Do you like salt?
1. I love salt
2. I add extra to food
3. I cook with it
4. Take it or leave it
5. I hate salt

This is the method Morrison's Supermarket has implemented. If you score over 10 you are a Non Taster. 7-9 is Normal and 6 and below a Super Taster. In trials at ThirtyFifty it is about 75% accurate. Super Tasters prefer fresher acidic white wines with lower alcohol and very soft reds such as Beaujolais Nouveau. They also enjoy wines that are sweet.

Normal Tasters may be able to drink tannic reds but prefer ripe reds and can enjoy wines with higher alcohol. Non tasters have the advantage of liking most wines, and are the most likely to enjoy Intense full bodied wines such as Bordeaux and Barolo.

A nice way to think about it is like a volume knob. Non Tasters have the volume of flavour turned down so they can enjoy most wines. While Super Tasters have the volume turned up and any harsh scratchy music is very uncomfortable. This has important implications for people who want to follow wine critics. There is no point following a critic who is a Non Taster if you are a Super Taster. All those Bordeaux recommendations that Non Tasters like are hard and horrible to Super Tasters. Similarly following a Super Taster critic while being a Non Taster will mean you will miss out on big Ozzie Shirazs and Bordeaux. This is one of the many reasons that you cannot believe a critic who rates a wine unless you have some experience with thier recommendations. Sadly the lowest common denominator is Fresh low alcohol white wines which means you miss out on many wines. I am on the low side of Super Taster, which unlike some of my compatriots means I dread having to taste a range of Barolo especially young ones, as I find the wines hard and horrible. Similarly young red Bordeaux is not pleasing to me and I tend to avoid these wines where possible. For years I have thought those going on about high end Barolo as being a bit of the emperors new clothes. I could not understand why I find them so displeasing while others raved about them. I now realise it is because those people are Non Tasters. Or another way their intensity volume is turned down.

For those who love Barolo Morrison's has decided to change the names, Non Taster are classed as people who enjoying intense wines. Smooth is the type for Normal tasters and Fresh for Super Tasters. This is less embarrassing for those who enjoy Intense wines. But there are some problems with this perhaps the most important is that it only catagorises wines by structure. While most people judge wines by the structure if you do not like the aroma you may still not like the wine. A full on Gewürztraminer may be great too for those who like the rose water / turkish delight flavours, but if it is not a flavour you personally like you will land up with wines you don't like.

The method employed by Morrison's to determine taste sensitivity is not 100% accurate and means some wines will be recommended when perhpas they shouldn't. At the very least if you are a Non Taster you are likely to be given a larger range of more extreme wines than you normally would. I think it is a move in the right direction.

Part 4 The aromas of wine

Our noses are amazing machines that can detect around 10,000 different aromas or more precisely defined as odours. An odour is a chemical that has evaporated into the air and is generally in very low concentrations. They travel in the air to the olfactory bulb either up through the nose if we smelling or down the throat and up to the nose if we are eating or drinking. In fact most of the flavour we taste is coming from our nose, not our mouth, which can only detect sweet, sour, bitter, salty, umami and heat. It may seem strange that some food can taste differently to how it smells, but this is because once wine or food has entered our mouth the temperature of our mouth changes the wine and changes what compounds are vaporised, changing the odour.

Once the odour has reached our nose it is detected by an olfactory receptor neuron, which transforms the odour to an electrical current. The odour receptor neuron is a G Protein-coupled receptor and works in a similar way to the G protein-coupled receptor in the mouth that detects sweet, umami and bitterness. The olfactory sensory neurons exist on a layer of tissue known as the olfactory epithelium. The epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body. The more olfactory epithelium you have and the higher the sensitivity of olfactory receptors, the more sensitive your nose.

Olfactory sensory neurons pass the electrical activity to olfactory bulb in the brain through nerve fibres. Once the electrical signal reaches the olfactory bulb which is part of the brain it process the smell and sends signals to other parts of the body. Smelling is made up of two parts, sensing the odour, then responding to it. For example the smell of food once detected may result in you producing saliva. 

How sensitive you are to particular smells will vary between humans and is controlled by the physical construction of your nose and how you have trained your brain. Humans have about 10 cm² of olfactory epithelium, whereas some dogs have 170 cm2. A dog's olfactory epithelium is also considerably denser, with a hundred times more receptors per square centimetre. So no matter how sensitive you are, you will never out-smell a dog! You can train your brain to be more precise in identifying different aromas and aroma kits are a great way for training your nose to discriminate between different aromas. But whether you detect them in the first place is based on physical limitations. The threshold that you detect a component is normally measured in parts per million with some smells easier to identify in lower concentrations than other.

The number of G protein-coupled receptors in our genome is thought to be around 350 in total shared throughout our body. But we can detect 10,000 different aromas so how can this be? It is because it is not a one to one relationship. A compound may trigger multiple receptors to fire, it is then up to our brain or more precisely, the olfactory bulb, to process this information and create the sense of aromas. This may be why two people can smell the same thing and think it is two aromas. But I suspect this is more to do with a lack of training the nose.

In many animals there is a second olfactory system known as the accessory olfactory system that is used to detect chemical signals between species. These are known as pheromones, these play no part in wine tasting and sadly for humans it would appear that the accessory olfactory system no longer works, it is known to form in the womb but is thought to fully develop. Although some scientist believes that pheromones are responsible for women’s menstrual cycle coming into sync if they spend time together. Human’s sense of smell is thought to have deteriorated during human evolution with Neanderthals having larger noses and more epithelium, meaning more sensitive noses.