The Science of Flavor

Before the World War II, sensory evaluation wasn’t a formal discipline at all. It was just something everybody did haphazardly. A food company would simply figure something either tasted good or bad.

“It’s a fairly young science,” said sensory expert Ken Baseman, Ph.D., of Papa John’s Foods and Grocery, who addressed Cactus IFT on May 18 about the role of sensory evaluation as an integral part of the development of new products in the food industry.

What is sensory evaluation? The standard definition, according to IFT, is the following: “Sensory evaluation is a scientific discipline used to evoke, measure, analyze, and interpret reactions to those characteristics of food and materials as they are perceived by the senses of sight, smell, taste, touch, and hearing.”

As Baseman began, he explained that sensory science supports key food industry areas like food safety and quality, product development and manufacturing. In addition, he said, it’s consumer testing where food sensory evaluation really resides.

What do we do with it? Baseman said sensory evaluation is used for shelf life studies, product matching, product mapping, specification and quality control, product reformulation.

Based on sensory evaluation, companies can provide general guidance for the selection, training and monitoring of assessors.

“If I really want to set up a program and I want to talk to my comrades across the world, then we have a set of standards that we can all follow,” Baseman said.

And you can’t talk about flavor without a background in sensory.

So, what are the basic types of sensory stimuli? They include appearance, color, odor, taste, touch, flavor, texture (eyes and mouthfeel). A recent addition is umame, which is a savory profile or more of a synergy of flavors. It’s part of what MSG is, but MSG had such a negativism that now they’ve changed the flavor’s name.

The physiology of taste comprises of sensations perceived through receptors on the tongue. In a classical sensory evaluation format, you would use salty for NACl, sugar for sweet, citric acid for sour, and caffeine for bitter.


When Baseman sets up a training program, he teaches people to recognize certain flavors at concentrations that are just above recognition thresholds.

“There’s a break where people say, ‘Gee, that’s not water anymore, but I don’t know what it is,’” Baseman said.

A familiar model for teaching sensory analysis is the anatomy of the tongue: a representation where bitter is tasted in the back, sour and salty coming along to the front, and sweet at the tip. Today, there’s discussion about all these sensory cites having the ability to distinguish each of the major tastes.

“There really is no one area,” Baseman explains that has a greater percentage of receptor sites that cause it to be more important to another. Instead, there is a great deal of taste interaction occurring across the tongue.

What exactly are taste interactions? It’s when one taste is used to modify another. For example, salt on melons can reduce its sweet taste, sugar in tea can reduce a bitterness, sugar in lemonade makes sour more tolerable, and removal of salt from tomatoes or savory products deadens the whole profile.

With today’s models we understand that “there are many combinations of locks and keys that make things happen,” Baseman said. “Once you make a contact, it allows other things to flow.”

Salt, for example, because of its low molecular weight, is able to get to more receptors and potentiates the flavor of everything else. It gets to specific sites not only on your tongue, Baseman explained, but even in your pancreas and throughout the entire body. It’s a universal catalyst for flavor.

“Once the lock and key come together, and the receptor allows the synapse to be tied, it potentiates other aspects, and they’re no longer independent entities,” Baseman said.

There are several factors that influence taste. One is age; when you get past 45 or 50 years old, the number of active sites decreases. Another is food; being hungry won’t influence it, but you shouldn’t try something after lunch since the food you ate may modify your taste sensations.

Smoking and obesity don’t necessarily decrease capability of sensory perception, but can influence flavor especially if disease or malnutrition is involved since it can affect ability to taste.

Temperature can also affect flavor. Salt is perceived as stronger as temperature goes up, bitter or sour is decreased as temperature goes down.

What about the nose and olfaction? In general we have much lower concentrations to detect odors than to detect flavors. The olfactory bulb in the base in the brain is triggered with olfactory sites back in the sinus area above the palate area.

“When you breathe in you actually bypass it, so the suggestion is that in order to best perceive odors, it’s best perceived by taking several quick sniffs,” Baseman said. “You really have to get those volatile systems up into the cavity for the perceptions.”

What about texture? The texture can influence taste too. In order to taste anything, it has to be solubilized, but if you have something that is textured, then it may interact with receptors that blocks specific flavor to get to sites.

A good example about texture is peanut butter. When you go from chunky to creamy you get smoother, spreadability. But the key texture attributes for peanut butter are: firmness, spreadability, adhesiveness, oiliness, dryness, and smoothness (lacks particulates).

“If you’re a wine snob, then you’re probably familiar with a wine flavor wheel, but you could have a wheel for tomatoes, a wheel for peanut butter, a wheel for anything you want,” Baseman said.

Taste Difference Tests

That’s it for physiology, so what about basic difference testing? The scope and application is to evaluate products and how they differ in any specific attribute to any degree. This is when the need comes for trained panelists. All evaluations should include some coaching ahead of time.

Among difference tests include the triangle, the duo-trio, paired directional test, and rating scale:

- A classical triangle difference test (“three blind mice, pick the one”) is when three samples are presented simultaneously: two identical ones and one different. The panelist is asked to identify the odd sample. The results indicate whether there is a detectable difference between the two samples.

- A duo-trio difference test is similar to the triangle, but the panelist is forced to select which sample matches the control.

- A panel directional difference test compares samples for one or more specific characteristics. Two samples are presented simultaneously or separately. The panelist is asked to identify the sample that has a greater amount of a specified characteristic.

- A rating scale difference test quantifies the degree of difference between a test and audit sample with a control of reference. It’s product specific and panelists must be trained for each product. Highly specific highly trained groups of people. This is where the outside sensory groups are basically taken over.

How many people are usually needed to do a proper sensory evaluation? The number 24 for trained people is regarded as the least number, or six people who do an evaluation four times.

A rule of thumb with untrained people, Baseman said, is to go to 50 people and using statistical scales get a valid standard deviation. When a test is wide, it’s really a “consumer panel,” instead of a procedure.

How does industry use sensory evaluation methodology? Baseman said it’s not all the same. What’s happened in the industry is that a lot of the entrepreneurial organizations talk, but it is not at all in a format.

Physical laboratory conditions for sensory testing should be carefully controlled to minimize bias therefore reducing experimental error. A testing area should be quiet and odor free. There should be a separation of people, keeping information away from panelists with booths or partitions that eliminates oral or visual communications.

Unfortunately, Baseman said organizations often suffer from “What does the boss say?” The syndrome involves the boss taking the sample and everybody else tasting it and agreeing with him or her. The sample is presented to a group meeting i a lab. Everyone stands around and chats as they taste and they all await the boss to begin the discussion.

“This is how you live and die. Don’t be fooled,” Baseman said, holding up a book that is at least 4 inches thick representing a four-day course.

“What did I used to do? I used to do flavor training,” he said. “We trained a new batch of people for the year. This way you should be able to avoid major catastrophes.”

When training bosses in the four-day program, he steered clear of saying something as blunt as, “you couldn’t tell an apple from an onion.”

Instead, he said, “we gave them basic tests, odorant recognition, intensity ranking, levels of sourness with increasing sweetness, levels of bitterness with increasing sweetness.”

He’d have seven different samples of sugar solutions that would start at 0 to intense, then he’d have people on staff who would take all the papers and crunch the numbers. This way, people would learn their limitations.

“Within an organization, you could tighten it up,” Baseman said. “This is the beauty of sensory evaluation.

“There’s a lot of companies that don’t do any of this stuff or very minimal,” he said.

Eventually, organizations could then train people regularly and create a sophisticated way to qualify ingredients in plants. As ingredients changes are made to any product, references could be sent out, and documentation provided. These measures would keep product quality and flavors consistent.