When using the sense of touch in the evaluation of food we often refer to the mouthfeel or texture of a sample. Although we will be focusing on tactile sensations in this blog, it is important to recognise that we start evaluating texture before we even touch a sample through cues from its appearance. We then continue to evaluate texture through in-mouth sounds. With that in mind, texture is really a combined perception using multiple senses.
The sense of touch is detected by receptors for temperature, pressure, pain and trigeminal irritation located in our skin and mucous membranes. Our skin is the largest organ of our bodies, about 20 square feet in an adult, but receptors for touch are unevenly distributed with the lips and tongue being two of the areas where they are most highly concentrated and therefore most sensitive.
Pressure receptors give us cues as to the geometrical properties of a sample; what shape is it, how dense is it, is it crystalline, liquid or spongy, sticky, powdery, mealy, crunchy?
Pain receptors tell us if something has damaged our membranes and gives us cues as to how sharp, rough or hard a sample is.
Temperature receptors detect the physical temperature of a sample; is it hot, cold, scalding, or varied in temperature?
Trigeminal nerve irritation can elicit mouthfeels such as prickling from carbon dioxide in fizzy drinks and burning sensations from the capsaicin in chillies. It can also include the eye watering when chopping onions and the heat and pungency in the nasal cavity when eating horseradish or mustard.
The texture of a product is key in flavour development as it is one of the things that affects the release of flavours. Firmer, colder, drier and thicker textured products tend to be slower to release flavours and aromas in comparison to softer, warmer, moister and thinner textured products. Manufacturers can take advantage of this to reduce the amount of flavouring they need to add to a product.
To test this theory yourself you can make up a packet of fruit jelly and add extra gelatine to half of the mixture. The firmer jelly will have the same amount of flavour there but will not release that flavour as quickly as the regular jelly.
When we consider the sense of touch in relation to the evaluation of food it includes how a sample feels upon handling, as well as texture and mouthfeel when eating a sample. Texture plays a role in the practicality of a product for various eating occasions. Manufacturers of on-the-go snacks have to take into account residues that may be left on the hands of consumers and the ability of a product to hold together during eating without utensils. Although packaging plays a large role in this, texture can also be manipulated to make products more user friendly.
Texture also gives us cues as to the freshness and quality of a sample. Take a potato chip as an example, it may look and smell as expected but upon biting have no crunch to it and thus indicate that despite appearances it is actually stale. Another example of this would be soda, whereby if it doesn’t produce a prickling or tingling sensation in the mouth it indicates that it has lost its fizz. Spend time in any produce section of a grocery store and you will see customers squeezing items of fruit and vegetables to test their ripeness and age.