December. 1928
INDUSTRIAL AND ENGINEERIR’G CHEMISTRY
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Research in the Confectionery Industry H. S. Paine C A E B O H Y D R A T E DIVISION, BUREAU OF C H E M I S T R Y A N D S O I L S . U ‘ A S H I N G T O X ,
H E teclinology of candy manufacture, in common with that of many other industries, has been developed on a rule-of-thumb basis. The candy maker, dealing continuously from day to day with a great number and variety of chemical and physical phenomena, has acquired a surprising degree of skill in making nice differentiations. He has applied this expertness in making fine distinctions in the trial-and-error method of experimentation, and in this way has developed the technology of the industry to its present status. I n spite of the general excellence of the many types of confections now on the market, there is a great opportunity for improvement, based upon more exact knowledge and application of the chemical and physical principles involved. Such an advance would place manufacturing technic upon a scientific and exact basis. So far as what may be termed esthetic factors, such as selection and blending of colors and flavors and artistic form of the confections, are concerned, the making of candy may properly be regarded as an art. I n its ideal state of development, the manufacture of candy would represent a happy combination of science and art. The candy industry is unique in the food field because of the great variety of materials used. These include many kinds of fruits and nuts, in addition to the more characteristic sugars which largely determine the physical consistency. The sugars are present in a great variety of physical conditions ranging from complete solution (as in liquid “cordial” centers) through intermediate amorphous states (as in “chewy” caramels and nougats) to states approaching supercooled melts (as in hard candy of very low moisture content). For many years chemistry has assisted the candy industry indirectly by improving the quality and increasing the variety of available raw materials, but only within recent years has this science been utilized to assist the industry directly and constructively. It is the purpose of this article to review briefly the general character of the chemical problems of primary importance in the candy industry, the nature of the chemical contributions so far made, and the probable character of chemical advances that may be expected in the future.
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aging of candy as in making iinproveinents primarily affecting the character of the candy when fresh. Control of Consistency and Texture
The chemist directly engaged in the confectionery industry has his greatest opportunityfor constructive workin controlling the consistency and texture of confections and in devising and formulating new types of texture and consistency. From the standpoint of physical structure, candies may be regarded as a mixture of sugars in various physical states which may serve as a matrix for holding fruits and nuts, this matrix being flavored and colored as desired. The nuts and fruits have comparatively little effect in determining the consistency and texture of the matrix, although in some cases specific effects may be noted. The most apparent effect is that of absorption or giving up of moisture. For instance, shredded coconut may absorb moisture from the candy matrix, a fact which must be taken into account by the candy maker. Some fruits, on the other hand, may yield enough moisture to dissolve an appreciable quantity of sugar, thereby altering the consistency. Acids in the fruit may cause some inversion of sucrose. Fats in chocolate-coated nut centers, especially \Then their melting points are lower than the average melting point of cocoa fats, may diffuse into the chocolate coating and cause a loss of luster and lightening of color known as “graying.” On the whole, hoxever, the consistency of confectionery is determined primarily by the character and proportion of the sugars used and the quantity of water present. The quantity of water depends primarily on the temperature to which the batch is cooked in its initial stage. This is well illustrated by fondant, a plastic material consisting of a solid phase of microscopic sucrose crystals and a liquid phase which usually contains invert sugar, corn sirup solids, and sucrose, being saturated with respect to the sucrose. Although the density and viscosity of the liquid phase affect the consistency of fondant, the most important factor is the relative proportion of solid and liquid phases. This ratio, in turn, depends upon the character and proportion of sugars and proportion of water present. Chemical Problems of the Candy Industry It is frequently desirable to increase the proportion of liquid In considering the basic materials used, it is apparent that phase to solid phase-i. e., obtain a softer consistency-in color and flavor play an important part in determining the fondant centers after they are coated with chocolate. This attractiveness of confections to the consumer. However, may be accomplished by adding a definite proportion of the improvements in the quality and diversity of colors and flavors enzyme invertase‘ t o fondant just before the fondant is cast are matters which concern the chemist of the producing in- or molded. The invertase causes inversion of a portion of dustries more directly than the confectionery chemist. On the sucrose in the liquid phase, thus increasing the proportion the other hand, certain phases of color effect, such as localiza- of invert sugar present. This increases total sugar solubility tion and inadequate distribution of color and so-called “fad- and permits a portion of the sucrose crystals in the solid ing” caused by crystallization of sucrose, are a result of phase to pass into solution. As a result, the quantity of factors which determine the consistency and texture of candy, solid phase is decreased and the quantity of liquid phase a subject that will be discussed later. increased, thus producing softer consistency. The invertase Some of the chemical problems of candy manufacture are, process, which is now extensively used, has the advantage of in reality, problems of other industries. This is well illus- accomplishing this change after the candy is finished and the trated by the fats, a wide variety of which is used. Rancidity fondant enclosed in chocolate coating, the degree of change of milk fat in caramels and of coconut oil in various types of being controlled (in view of the rather restricted temperature candy in which shredded coconut is used is of importance to range and fairly definite time period intervening between prothe candy manufacturer, and means of controlling and retard- duction and consumption) by the quantity of invertase added. ing rancidity would be of great assistance in prolonging shelf It is evident that the solubility and saturation relations a t life and retarding aging. The function of the chemist in the 1 Paine, I N D ENG CHEM, 16, 513 (1924); Paine and Hamilton, U. S . candy industry lies as much in devising means of retarding Patents 1437,818 (1922) and 1,502,207 (1924).
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
different temperatures of the various sugars present furnish the key to the consistency which may be obtained in making fondant confections. This is likewise true of candy of other types. These relations are also the determining factor in the deterioration due to loss of moisture in aging. Consistency vitally affects the character of the confection and is a subject in which the chemist is preeminently qualified to guide the candy maker. In some kinds of candy of amorphous structure, such, for instance, as caramels, in which milk is used, the milk solids also play an important part in modifying consistency. I n candy of other types the character of the consistency is determined primarily by the presence of starch, egg albumin, and gelatin. The tendency of candy to undergo fermentation is closely allied to the subject just discussed. Candies containing a liquid phase of relatively low specific gravity are especially subject to fermentation. Losses in the candy industry from this cause have in past years amounted to a considerable figure. Investigation* of certain phases of this subject (in fondant candies) has shown that the most characteristic type of fermentation is that caused by torula-like yeasts, which are capable of growing in solutions of unusually high density. Even these yeasts, however, were unable to function actively in sugar solutions of very high density. The critical point was found to be a t about 79 per cent solids content. The character and proportion of sugars used, therefore, are factors of determining importance, as they primarily influence the solids content of the liquid phase a t the sucrose saturation point. This fact suggests that the remedy3 lies in a formula calling for proportions of sugars required to yield a density of liquid phase corresponding to a t least 79 per cent solids. I n most types of fondant candy subject to fermentation, this result can be attained by replacing a portion of the sucrose by invert sugar, either by changing the proportion of the original ingredients or by using invertase to invert a portion of the sucrose after the candy is finished. The latter course is often preferred and usually accomplishes the desired result, except occasionally when infection by yeast is so pronounced and fermentation gets under way so rapidly that increase in density of the liquid phase due to inversion does not proceed rapidly enough to check it. As the production of only a small quantity of gas is sufficient to burst the chocolate coating and ruin the confection, it is necessary that fermentation be checked a t the very start. The hygroscopic character of the raw materials used and the tendency of the finished candy to absorb or give up moisture in reaching equilibrium with varying atmospheric humidity vitally affect the shelf life of candy. In fact, aside from such factors as rancidity of fats which may be present and “graying” of chocolate coating, the principal feature of aging is loss of moisture. It is possible, by careful control of the proportion and character of ingredients and method of manipulation, to retard the loss of moisture and thus increase to a marked degree the shelf life of certain candies. Some types of candy lose moisture and age much more rapidly than others, but in all cases there is a possibility of retarding the aging to some extent. As levulose is exceedingly hygroscopic, especially in the presence of certain other substances, the use of invert sugar tends toward retention of moisture. The use of invertase in fondant, in addition to the advantages already mentioned, retards aging due to increased retention of moisture by the invert sugar produced. The incorporation of colloidal substances, with pronounced water-binding power, such as egg albumin, gelatin, and pectin, may also be beneficial from this standpoint in certain types of candy. I n candies of the fondant type or those that contain a liquid phase saturated with sucrose, loss of moisture causes 2
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Church, Paine, and Hamilton, IND.ENQ.CHBM.,19, 353 (1927). Paine. Birckner, and Hamilton, Ibid., 19, 358 (1927).
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supersaturation and resulting crystallization of sucrose, thus increasing the proportion of solid phase and decreasing the liquid phase. The candy therefore becomes harder and drier. I n candy like “chewy” caramels, especially when too much sucrose is used, loss of moisture may be sufficient to cause enough sucrose to crystallize to change entirely the consistency of the product. This change is seen in the transition of a “chewy” caramel into a “crumbly” one. In hard candy, which, when fresh, may contain as little as 1 per cent of water and contains sucrose in a condition resembling that of a supercooled melt, the absorption of a small amount of moisture on the surface greatly accelerates the transition of sucrose into a crystalline condition. As a result, the hard candy loses its luster and transparency, and finally, as a result of sucrose crystallization, reaches a consistency where it crumbles readily instead of breaking with the vitreous fracture characteristic of it when fresh. Absorption of moisture may also ruin the consistency of candy. If the candy contains a characteristic liquid phase, the liquid phase is increased unduly in proportion to the solid phase. In other cases ruin may be brought about by production of a liquid phase in candies not normally of this type. Proper Packaging
The question of packaging, particularly for goods to be shipped or held in stock for any length of time, is very important, and is closely allied to the problems of consistency, texture, hygroscopicity, and drying, which have just been discussed. The problem of retarding aging in candy can, so far as loss or absorption of moisture is concerned, be solved to a considerable extent by proper packaging. Candies of low moisture content, such as hard candy, are best packed in hermetically sealed containers. The quantity of moisture contained in the candy, even if yielded freely to the atmosphere in the container, is hardly sufficient to cause saturation with aqueous vapor, and even a t reduced temperatures does not result in “sweating.” On the other hand, candy of relatively high moisture content, such as that of the fondant type, especially bonbons, which do not have any protective coating other than a special kind of fondant, cannot be packed in hermetically sealed containers on account of a pronounced tendency to “sweat,” due to saturation of the air in the container by moisture lost from the candy and subsequent deposition of moisture a t reduced temperature. Such candies must be packed in loosely closed containers, SO that the moisture evaporated from them may be released to the outside atmosphere and not confined in the package. Under such conditions the candy may dry out rapidly, but this is preferable to “sweating.” Other candies of intermediate type are best packaged in fairly tight containers, but not hermetically sealed, thus causing a lag in attaining humidity equilibrium with changing outside atmosphere. There is distinct opportunity for fruitful research in devising means of proper packaging of candy of different types. The ideal package for candies of high moisture content would be one provided with a valvular opening, the closure of which could be regulated automatically by variation in atmospheric temperature and humidity. Even if this type of package should be unattainable, it should be possible to improve present methods of packaging. Application of Colloid Chemistry
Among the great variety of physical states and consistencies represented by various types of candy the colloidal condition is well represented, marshmallow furnishing one of the most typical examples The choice of ingredients in this case is primarily for the purpose of furnishing a medium in which to emulsify a large quantity of air, a t the same time providing
December, 1928
INDUSTRIAL A N D ENGINEERING CHEMISTRY
an agreeable flavor. The addition of materials, such as gelatin and egg albumin, to a viscous medium obtained by the use of sucrose, corn sirup, and water serves to reduce surface tension, and when the mixture is violently agitated a large proportion of air is incorporated in the mass. This incorporated air produces both lightness of texture and white ness of color. The problems of marshmallow manufacture are primarily those of texture and stability. Both depend to a great extent upon suitable water content, which, in turn, is influenced by the other constituents. There are many colloid problems in the candy industry, and the facts and principles of colloid chemistry find ever-increasing application. Use of Chocolate
Chocolate, which is one of the most important ingredients in many candies, presents a large number of problems. Although chocolate is relished by most persons for its agreeable consistency and flavor, its extensive use in the candy industry has resulted from other considerations as well, the most important of which is the fact that it serves as an excellent protective coating, which, on account of its high fat content serves to retard evaporation of moisture from the coated center. This protective feature is so important that, if a suitable substitute for chocolate were ever provided, the use of chocolate would in all probability decrease. The candy industry uses most of its chocolate in the form of coating, and, aside from considerations of flavor and color, the candy manufacturer is principally concerned with the fluidity of the chocolate coating. The fluidity should be sufficiently high and sufficiently uniform, particularly in coatings to be applied mechanically by means of enrobing machines. Although the fluidity is determined to a great extent by the quantity of cocoa fat present, the fineness of milling and the extent to which the individual cacao particles in the mass are enveloped by fat undoubtedly play an important part. The fluidity of chocolate coating is a subject which has not been investigated adequately. New Types of Candy
I n some fields of manufacture, industry is best served by the mass production of standard articles. I n others, there is danger of too much standardization, and the continued pro-
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duction of novelties and new types is vital to success. Old favorites will doubtless continue to play an important part in the stability of the candy industry, but there is also an urgent need for the production of new types of confections. The problem of producing new confections, so far as it involves combining and blending basic raw materials, flavors, and colors from the standpoint of their gustatory and esthetic appeal to the consumer, belongs more to the creative chef or candy maker than to the chemist. The appropriateness of texture and consistency, the constancy with which the desired consistency can be obtained, and the stability with which i t may be retained, however, are essential and vital features in any confection, new or old, and it is here that the chemist has an indispensable function in the creation of new confections. An excellent, illustration of this is in the production of a new type4 of candy containing dextrose instead of sucrose in the solid phase, the liquid phase containing levulose and being saturated with respect to dextrose. This is a distinct novelty, in that in all the usual types of candy containing both liquid and solid phases the solid phase consists of sucrose. On account of the difference in physical characteristics of dextrose and sucrose crystals, a confection of this type has a consistency quite different from that of candies containing. sucrose as the solid phase. Conclusion
Chemistry as so far employed in the candy industry has been used primarily for the purpose of analysis and control, and even then it has been restricted to certain phases of manufacture, especially to the control of dyes to obtain the desired shades. The field of application of chemistry in a constructive and creative way, to devise new types of. confections, to obtain suitable consistency and texture, to retard aging, and to design appropriate types of packages has hardly been touched. Herein lies a definite opportunity. The situation demands active cooperation between the chemist and the candy maker. As in other industries, the “practical man” often depreciates the value of the chemist or other technical man, and the chemist frequently views so-called “practical” knowledge with some disdain. It is undoubtedly by close cooperation between the two that the greatest and most rapid progress can be made. 4
Schneller, U. S. Patent 1,551,175 (1925).
Catalysts for the Formation of Alcohols from Carbon Monoxide and Hydrogen 11-Synthesis of Methanol with Catalysts Composed of Copper and Zinc’ Per K. Frolich, M. R. Fenske, P. S. Taylor, and C. A. Southwich, Jr. DEPARTMENT O F CHEMICAL ENGINEXRING, MASSACHUSETTS INSTmUTE
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HE recently developed processes for the high-pressure
synthesis of alcohols and other organic products from water gas owe their success primarily to the develop ment of a new type of catalysts composed of mixtures of metallic oxides a t various stages of reduction. The lack of detailed knowledge concerning the reactions involved in this promising field of industrial chemistry warrants a careful study of the fundamental nature of the metallic oxide catalysts employed. I n initiating an investigation along this 1 Received July 24, 1928. Presented before the Division of Industrial and Engineering Chermstry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928.
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line, data were obtained on the decomposition of methanol in the presence of catalysts prepared from the oxides of copper and zinc in various proportions, ranging from 0 to 100 mol per cent of each constituent. The results of this work, published as the first paper of the present series,* showed that there was a profound change in mechanism of the decomposition reaction in going from 0 to 100 mol per cent zinc oxide. Thus, while pure copper gave predominately formaldehyde, the addition of a small percentage of zinc oxide to the catalyst resulted in methyl formate production with a maximum yield a t about 88 mol per cent copper and 12 mol 2
Frolich, Fenske, and Quiggle, IND.ENG.CHEW.,SO, 694 (1928).
