Institute of Food Research
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK
www.ifr.ac.uk Tel: +44(0) 1603 255000 Fax: +44 (0)1603 507723
Taste and Flavour
Taste and Temperature
- Recognise other senses that contribute to perception of food.
- Give examples of foods and drinks that taste differently at different temperatures.
- Describe how chemicals can create a sense of hot or cold.
- Distinguish between sensing temperature and sensing chemicals in the mouth.
Key words: Trigeminal nerve, hot, cold, temperature, menthol, sorbitol, chilli, capsaicin, Scoville
Temperature is an essential element of human taste experience. Food and drink which — within a given culture — is considered to be properly served hot is often considered distasteful if cold, and vice versa.
The perception of taste is influenced by the temperature of foods. In some people, stimulation of the tongue with different temperatures can produce different tastes. Warming the front of the tongue produces a sweet sensation, while cooling can produce a salty or sour sensation. Our taste sensitivity is enhanced with increased temperature explaining why warm beer tastes bitterer and warm cola is sweeter. The flavour of foods is also enhanced with increasing temperature as more volatile chemicals are released to be detected by the olfactory system.
Many of the sensations that affect taste are detected by the trigeminal nerve including substances, temperature and texture.
Some sugar substitutes cause cooling as they dissolve in solution e.g. saliva. Sorbitol, xylitol and mannitol often found in mint sweets or chewing gum not only stimulate sweet receptors but also cause a cooling sensation detected by temperature receptors.
Some substances activate taste cell receptors connected to the trigeminal nerve. These receptors respond to substances found in spearmint, menthol, ethanol or camphor producing a cool sensation referred to as “fresh” or “minty”. The substances in the food activate the TRP-M8 ion channel on nerve cells that signal cold. This receptor is also known as the cold and menthol receptor 1 (CMR1) and as the name suggests it senses both temperature and menthol molecules.
There are therefore two forms of cold sensation, that caused by a change in temperature and that caused by chemicals such as menthol.
Spiciness or ‘heat’
Substances such as chilli and capsaicin activate a different receptor connected to the trigeminal nerve, TRP-V1. This is a nerve cell ion channel that is also activated by heat. The burning sensation, usually referred to as “hot” or “spicy”, is a notable feature of Mexican, Indian, Tex-Mex, Szechuan, Korean, and Thai cuisine.
The two main plants providing this sensation are chilli peppers (those fruits of the Capsicum plant that contain capsaicin) and black pepper. Spicy foods are measured on the Scoville scale in Scoville heat units. This scale was developed in 1912 and involved a panel of tasters, nowadays the concentrations of ‘heat’ inducing chemicals can be measured with high-performance liquid chromatography (HPLC).
The Trigeminal (or cranial V) nerve endings in the tongue, mouth and nose are stimulated by a variety of chemical ‘irritants’ including chillis. The receptors detect ‘pungent’ chemicals that give sensations of
Heat – Chilli, Pepper, Mustard, horseradish
Astringency – Onion, Garlic
Alcohol – Vodka, Absinthe
The trigeminal nerve carries signals to and from the face. There are trigeminal nerve endings that detect irritation to the eyes such as chopped onion and in the nose, for example causing a sneezing response to sniffing pepper.
Prepare cool and warm water and ask pupils to compare their sense of taste with the five basic tastes. This can be done by pupils dipping their tongue in warm water for a few seconds and then after a short break to let the tongue return to body temperature repeating it with cold water. Not all pupils will experience a thermal taste response, though sweetness is most common among those that do.
After this introduction to the effect of temperature, the effect of chemicals inducing sensations of hot and cold can be investigated.
Pupils can choose to taste Tabasco Sauce and some peppermint to demonstrate false hot and cold.
Extension activity: Pupils can then try chopping onions to see if they are sensitive to eyes watering and then compare their results later with the results of their genetic taste tests. Ask pupils to formulate a hypothesis about the relationship between trigeminal nerve sensitivity and genetic super tasters.
What you will require
• Tabasco sauce or chilli sauce
• Drinking water
• Chopping boards
Health and Safety
Ensure the temperature of water for tasting is not so cold or hot as to cause discomfort. Provide pupils with individual receptacles for tasting water. Make sure pupils do not have too much Tabasco as they are often unaccustomed to the strength and are more sensitive than adults. Also make sure there is water available to drink straight away.
New Scientist. Why Don’t Penguins Feet freeze? Pages 113-114. Ed. Mick O’Hare, 2006, Profile Books Ltd.
New Scientist. Do Polar Bears Get Lonely? Pages 12-13. Ed. Mick O’Hare, 2008, Profile Books Ltd.