Tharp's Food Technology
How to be a Knowledgeable & Discriminating Ice Cream Gourmet
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Bruce W. Tharp, Ph. D.

Based on a presentation by the author at the Smithsonian Institution Campus on the Mall Program, "Ice cream, Ice Cream: Food Fit for the Gods", Washington, D.C., USA, July 23, 1994.
Copyright © July 2002 by Tharp's Food Technology.

Ice cream has evolved from a simple mixture of ice and fruit juice said to have been enjoyed by the Romans in the time of Nero (and by citizens in what is now China long before that).  It is now a product that combines dairy ingredients with other foodstuffs and food ingredients.  The process of doing so involves the application of sophisticated processing techniques to produce a complex mixture of the following components:

Ice cream - a complex mixtureAlmost limitless lipids (a.k.a. fats);
A profusion of proteins;

A collection of carbohydrates;

A melange of minerals;

A variety of vitamins;

An accumulation of air;

A phantasmagoria of phlavors; and

A wonderland of water, with all three phases present - liquid, solid and vapor. 

The first step in making any ice cream is to calculate the precise amounts of individual ingredients that will be needed to make a specific ice cream formula.  These ingredients are then  blended together into a liquid mixture called "ice cream mix" or, simply, "mix".  The mix is then heated to a specific temperature and held at that temperature for a time that is specified by food safety regulations to accomplish pasteurization.  That process kills all pathogenic microorganisms that may have been in the liquid mix.  It also brings about subtle changes in the flavor and structure of ice cream components.  Those changes are essential to creating the distinctive properties associated with a specific brand of ice cream. 

Following pasteurization, the hot mix is homogenized to bring about an intimate association of all the components and achieve a permanent uniformity.  That is accomplished by  forcing the hot liquid through a very small orifice at high pressure - over two thousand pounds per square inch.

After the pasteurized and homogenized mix is cooled, it is then aged for anywhere from a few hours to overnight in order to achieve the final interaction of all the ingredients into a form that is needed for the perfect ice cream.  The mix is now ready to be converted into the ice cream we enjoy.

The first step of that process is known as "freezing", during which the conversion of water to ice begins.  Freezing occurs progressively as the mix passes under pressure from one end of a very cold stainless steel cylinder to the other.  As ice forms on the surface of the cylinder it is removed by sharp blades moving over the surface at a high speed.   During the passage through the freezing cylinder air is whipped into the ice cream.

The air component of ice cream is so critical to desirable properties that its presence is required by U.S. Food and Drug Administration (FDA) regulations.  The amount of air incorporated is referred to by the industry as "overrun".  Overrun is expressed as a percentage, and refers to the relative volumes of air and mix in the package.  For example, ice cream in which the volume of air is exactly equal to the volume of mix is said to have 100% overrun.  When overrun is properly incorporated, it is in the form of finely divided and evenly distributed air cells that help provide structure and creaminess.  In that form, air makes a key contribution to the pleasing properties of ice cream. 

The semi-frozen product emerges from the freezing/whipping equipment with two components that  were  not  present in  the liquid  mix - air  and ice.  To achieve specific flavor properties, the basic mix can be flavored with its characterizing flavoring before it is frozen.  Further flavoring materials such as fruits, nuts, candies, syrups etc. can be injected into the semi-frozen product before it is packaged.  

The final process, which is applied after packaging, is known as "hardening".  In this process, the packaged product is subjected to extremely low temperatures - as low as forty degrees below zero - in equipment designed to cool it rapidly .  (Rapid cooling is an important element in the development of the extremely small ice crystals that are necessary to give ice cream a smooth, creamy texture.)

With that general background, we are ready to examine the process of ice cream evaluation.


The organized sensory evaluation of dairy products has been an important factor in the development of the dairy industry.  Its application began as a tool for grading dairy products in order to associate selling price with quality.  That activity continues today - the grading of  butter, cheese and other dairy products through the application of sensory evaluation by the United States Department of Agriculture is still an important part of the economic structure of the dairy industry.

The basic concept of official judging is that a perfect product is one in which no defect can be detected.  For each product, a list of recognized terms that describe specific properties has been established.

Ice Cream Sensory  Evaluation Targets

The ultimate enjoyment of ice cream is an experience that is the result of perceptions provided by the simultaneous application of multiple senses.  The focus in this section will be on the following characteristics, each of which will be discussed individually: appearance, flavor, body, texture and melting properties.


The view of a freshly opened package of ice cream should show that the package is completely full.  The surface of the product (or that of a freshly dipped portion) should be homogeneous in appearance and show a color that is consistent with its declared flavor.  When fruits, nuts, syrups etc. are incorporated, they should be uniformly distributed. 

Descriptive terms for appearance characteristics:

Unnatural color

This term describes a color that is inappropriate for the flavor by which the ice cream is identified.  For example, it would be applied to strawberry ice cream that has a strong purple tinge, or a peach ice cream that shows excessive red color. 


This is a condition where slight variations in the color or visual texture can be seen.  It can result when several streams of ice cream of slightly different characteristics have been combined at the point of filling the package, and each has retained its identity.

Poor distribution

This is the term used to describe the uneven dispersion of added materials - fruits, syrups, nuts, candies etc. - into the ice cream.  They should be spread throughout the product in a uniform way.

Lacks _______________ (fill in the blank with the appropriate material - syrup, nuts fruit etc.)

This term requires little elaboration.  It is used when the quantity of added material does not fulfill your expectations.

Package not full

On rare occasions you may notice that when you open a carton of ice cream it does not completely fill the package.  There are two primary causes for that condition.  A short fill results when the packaging equipment was out of adjustment and the proper amount of product was not added.

If the ice cream appears to have pulled away from the sides of the package, the condition is known as shrinkage.  Shrinkage is the result of a weakness in the structure of the air cells in the product that has allowed the ice cream to collapse inwardly as the air cells lose their identity.

Package too full

Improperly adjusted filling equipment can add too much product to a carton, producing a bulged appearance.


The sensory evaluation of flavor properties should be applied in a way that  covers the full range of flavor characteristics - both those of the basic ice cream mix, and the added characterizing flavoring ingredients.   That is not an easy objective to accomplish with some ice cream flavors.  Many of these contribute strong and distinctive flavors of their own.  While these flavors add to our overall enjoyment of ice cream, their presence can mask some of the delicate dairy-derived flavor characteristics of the product. 

Vanilla is a flavoring that has minimal interference with the dairy flavor notes in ice cream.  Good vanilla flavorings add a subtle note that blends with the dairy flavors without interfering with their perception.  For that reason, vanilla is the flavor of choice for general evaluations.  Its delicate flavor allows for the intimate evaluation of all of the subtleties of the basic dairy flavor profile present in the ice cream mix that are masked by the presence of the more robust flavoring ingredients.

There are two components to the flavor characteristic -  taste and aroma.  Taste is perceived in the mouth - more specifically, on the tongue.  It includes the  sweet,  salty, sour  and bitter characters.    Aroma, which is perceived in the nasal  cavity, includes all other elements of flavor.  It is the aroma properties that characterize flavor.  Without aroma, it would not be possible to distinguish strawberry ice cream from peach, or butter pecan from toasted almond.

Descriptive terms for ice cream flavor characteristics:


The cooked flavor is a milk custard character associated with the use of higher than normal temperatures in the pasteurization of the ice cream mix or some of its ingredients.

Lacks freshness/old ingredient

These are two degrees of an unpleasant stale character that develops during the storage of dry dairy products such as nonfat dry milk, dried buttermilk and dried sweet whey.

Lacks/too high flavoring or sweetness

These terms are self-explanatory and require no elaboration as to their nature.

Lacks fine flavor

This term describes a flavor system  that, while pleasing, falls short of the perceiver's concept of perfection.


"Unnatural" is used to describe a flavor system that provides a  character that departs from the expectation created by the name of the flavor. 

In considering the presence of an "unnatural" flavor, it is useful to know that the phrase describing the flavor of packaged ice cream provides a clue as "naturalness" of the flavoring used.  FDA has defined three categories of ice cream  flavorings for labeling purposes, which differ in the degree of "naturalness" of the flavoring system.  The application of the FDA definitions is shown in the following examples using vanilla:

Vanilla ice cream (Category 1) is flavored only with pure vanilla flavoring;

Vanilla flavored ice cream (Category 2) is flavored with a blend of pure and imitation vanilla  flavoring, with the pure vanilla predominant; and

Artificially flavored vanilla ice cream (Category 3) is flavored with a blend of pure and imitation vanilla flavoring, with the imitation flavor predominant.


Not unexpectedly, a salty flavor can result when excess salt is used.  However, saltiness is also associated with the use of a high level of milk solids not fat (MSNF, or the solids component of skim milk) in the formulation.   MSNF contains a significant level of minerals that can contribute a noticeable salty character at higher levels of use.


The "syrup" flavor is associated with the  presence of corn syrup sweeteners derived from corn starch.  Karo™ syrup is a consumer version of this form of sweetener; its flavor is often used as a reference point for the syrup flavor in ice cream.


It is regulatorily and aesthetically acceptable to add good quality whey solids as a portion of the MSNF component of ice cream.  High  levels or poor quality of the whey solids ingredient used can produce an off-flavor reminiscent of alfalfa hay or graham crackers.


This denotes the presence of a flavor characteristic completely alien to the character of the flavor designation for the ice cream.  For example, if an ice cream identified as strawberry has a cherry flavor, the term "foreign" would be appropriate to describe that condition. 


A situation where the flavor very rapidly rises to a peak, and is perceived to have an unpleasant sharpness.


These terms are used interchangeably to describe the perception of the emergence of  flavor from the ice cream as it melts in the mouth and releases the volatilized flavor compounds into the nasal cavity.  It is usually used with appropriate qualifiers - delicate, light, full, rich, etc.


Ice cream - bodyThe term "body" refers to the cohesiveness of the product as it is being served and consumed.  It is an indication of the overall structure of the product.

Descriptive terms for ice cream body characteristics:


Weak ice cream lacks substance and offers little resistance to manipulation in the mouth.


The antithesis of weak - a character where the product may string out when dipped, and feels sticky in the mouth, reminiscent of eating a gumdrop.


This characteristic is best observed in the dipping or spooning process.  In crumbly ice cream, the structure breaks apart readily when it is dipped, making it difficult to remove portions without small pieces falling off.


A "short" body shows lack of cohesion to a degree less than that of the crumbly condition.


"Fluffy" is a light, marshmallowy character associated with high levels of air incorporation, or the use of conventional levels of air in the form of larger than desirable air cells.


This is generally a positive term.  It is used when the ice cream resists the loss of structure as it is manipulated in the mouth, but not with the persistence that would be associated with gumminess.


Ice cream - texture"Texture" refers to the relative smoothness of the ice cream perceived as it is being manipulated in the mouth.  This characteristic is directly related to the size  of crystalline material present.  All ice cream contains these crystals, either as a result of the freezing of water into ice or through the crystallization of  some component of the sugars present. The roughness that is observed when perceptible crystals are present is generally felt to be a sign of diminished quality.  That loss of quality is directly related to the size of the crystals - the larger the particles, the poorer the quality.  Most fresh ice cream has a silky smoothness, because the crystals are so small that they cannot be detected.  

For ice cream in which absolute smoothness is considered to be a hallmark of quality, the trick for the ice cream manufacturer is to keep the consumer from noticing the ice in the product in any way other than its coldness.  That situation changes when ice cream is exposed to fluctuations in temperature during shipping or storage.  The industry calls that temperature fluctuation "heat shock".  It causes the ice crystals to grow, and if it is severe enough they grow to a point where they can be detected as the ice cream is eaten.  Instead of the smoothness associated with small ice crystals that is the sign of good quality, large ice crystals produce a roughness that many find unpleasant.

Some ice cream manufacturers strive to produce an ice cream in which the size of ice crystals is such that they can be ever so slightly detected.  The slight lack of smoothness in such products is marketed as an "old fashioned" ice cream character. 

Descriptive terms for ice cream texture characteristics:


These two terms are used to describe a lack of smoothness produced by the untoward growth of ice crystals.

"Coarse" describes a condition in which only a very slight roughness due to the presence of ice crystals can be perceived.  An "icy" ice cream  is one that shows a more severe manifestation of the coarse character.


"Sandy" describes a grittiness similar to what would be produced by fine grains of sand.  It is caused by the presence of perceptible sugar crystals, usually the native milk sugar - lactose. 


This term is used to refer to a condition in which a film of milk fat is perceived in the mouth or on the lips as the ice cream is being manipulated.  It results from the presence of large agglomerates of fat that have developed under the rapid agitation that is applied during the whipping and freezing process.

In general, but by no means absolutely, ice cream consumers in Europe seem to accept a degree of fat agglomeration as creaminess that in North America would be described as greasy.

Body/texture combination

The simultaneous evaluation of body and texture characteristics provides an overall perception of a quality often described as "richness".


The term "meltdown" refers to the behavior and appearance of a portion of ice cream as it melts.  Ideally, the melted product should be a smooth, homogeneous mixture resembling ice cream mix before freezing.

Descriptive terms for ice cream meltdown characteristics:


This term describes the presence of a significant degree of air bubbles in the melted product.  The presence of excessive air is considered a defect.

Too fast/Too slow

The rate at which ice cream loses its shape during melting can provide an indication that is often related to other characteristics that are observed during sensory evaluation.  A very rapid loss of shape, usually referred to as a "fast" meltdown, is often associated with weak-bodied products.  The retention of shape by a portion of ice cream long after all the ice has melted is referred to as "slow" meltdown. 


The term "curdy" is used to describe a condition in which flecks of material appear on the surface or within the melted product.  These flecks are produced by the destabilization of the protein or fat system as a result of the stresses to which they are exposed during the processing of the ice cream mix, or one or more of its dairy ingredients.

Techniques for performing a discriminating sensory evaluation

Evaluation steps for vanilla ice cream (By making appropriate adjustments, it is possible to apply these techniques to other flavors as well.)

1. Observe the color and uniformity of the product. 

2. When practical, set a small amount aside on a plate for later evaluation of melting behavior.

3. Remove a portion - about a teaspoonful - from the general mass of the ice cream.  As it is separated, pay close attention to the behavior of the portion with respect to its body properties.   Transfer the portion to the mouth.  As you begin the oral manipulation of the portion, remember that many of the desirable properties of ice cream are related to the amount of ice present and the size of the ice crystals, so focus first on those properties - body and texture.  Taste and aroma perceptions should be filed away for later recall.

4. Bite down through the portion with front teeth (if dental sensitivity permits!) – iciness will be reflected by the perception of a crunchy sound. 

5. While moving the portion about in the mouth with your tongue, cheeks and lower jaw, and concentrate on the degree of resistance to that movement (body) and the smoothness of the still frozen sample (that's the texture).

6. Don't swallow after the ice cream melts.  Instead, with closed mouth, concentrate on the flavor, first on the taste perceived in the mouth (sweetness, saltiness, bitterness and tartness/acidity).   It is at this stage that the greasy character will be perceived as a slippery coating on the inner surfaces of the mouth, particularly the teeth.

7. With the mouth still closed, exhale nasally in order to expose the vapors released from the warming product to contact the aroma perception area in the back of the nasal cavity.  Concentrate now on whether the perception is pleasant or not.  If not, why not?  (Think about the descriptors discussed earlier.)

8. In professional evaluations, the portions of ice cream are not swallowed, but are expectorated into a suitable container.

9. Regardless of whether the sample has left the mouth in an outward or inward direction, allow a period of time to reflect on the flavor sensations it has left behind.  These residual perceptions are referred to as "aftertaste", and make up an important element of the overall flavor judgment.  A good quality product leaves behind a fresh, clean sensation, consisting only of lingering hints of the characterizing flavor and the basic dairy character.  The time during which these observations are made is referred to as the "clean-up" period.  Products are described as "cleaning up" well or badly.  If a greasiness was noted during earlier manipulation, the coating will persist and remain noticeable during clean-up.

10. Repeat 3 - 9, if necessary.  In so doing, beware of spheno palatine ganglioneuralgia, a condition commonly known as "ice cream headache".  (Note - that term is known only to the most knowledgeable of ice cream buffs; its use in casual conversation is bound to impress!)

11. Finally, solemnly and knowledgeably announce your comments about the product to your companions.  By this time, it should also be appropriate to observe and comment about the melting behavior.

12.  When evaluating more than one sample of ice cream, it is useful to cleanse the mouth with bland, room temperature water between samples.  This will remove any flavor influences left over from the previous sample, and avoid the desensitizing influence of coldness by hastening the return of the mouth to normal body temperature.

It should be kept in mind that none of the standards described here is absolute. The important position to reach is the development of a true understanding of what characteristics constitute the ideal ice cream for yourself, then develop the discriminating ability to identify the degree to which those characteristics are present in whatever product is before you at any given moment.

I scream, you scream, we all scream for ice cream, ...TECHNIQUES FOR THE CONVENTIONAL CONSUMPTION OF ICE CREAM

1.  Transfer a reasonable portion to the mouth.

2.  Chew and otherwise manipulate in the mouth.

3.  Swallow as necessary.

4.  Repeat 1 - 3 until the sample is depleted or the point of satiety has been reached, whichever comes first.

    Finally,........ ENJOY!!