This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Though the amount of sugar added to chocolate liquor varies greatly and the blends of chocolate are unlimited, Zenlea makes the following classifications of general types: bitter-sweet, dark-sweet, medium-dark sweet, light-sweet, milk, ice cream bar, skim milk, buttermilk, malted milk, imitation, and lecithin coatings. Bywaters states that the tannin group of substances is a very important constituent of cacao matter, "for it determines to a great extent the colour and the taste of the product. Cacao catechin and cacao tannin are present in the fresh unfermented bean." The catechin gives a very bitter flavor. Adam and Jensen have both determined the amount of catechin and cacao tannin in the unfermented bean and in the manufactured chocolate and cocoa. During fermentation the cacao catechin is transformed to cacao tannin. The amount of cacao tannin found in the fully fermented beans averages 1.9 per cent.
Bywaters states that cacao tannin in the presence of oxygen is transformed into a phlobaphene, which is insoluble in water and reddish in color. The red color of cocoa is chiefly due to the presence of this phlobaphene.
To make cocoa the chocolate liquor is put in a hydraulic press and part of the cocoa butter is removed, leaving a cake containing less than one-half as much cocoa butter as the chocolate. This cake is pulverized.
Cocoa. Zenlea states that there are many kinds of cocoas, but depending on processing they may be separated into two main classifications: (a) natural and (b) Dutch.
Natural-process cocoas have had no alkalies or "Dutching agents" added during manufacture. Schaal states that probably about 75 per cent of the cocoas used by bakers are natural-processed cocoas. Some chocolate is also "Dutch" processed.
Dutch-process cocoas have been treated with an alkaline solution such as potassium carbonate, ammonium bicarbonate, or sodium carbonate or bicarbonate. In some instances, according to Zenlea, the cleaned nibs are actually boiled in an alkali solution as strong as 3 per cent, based on the weight of the nibs. In commercial practise 2 per cent of alkali is more commonly used. To complete the treatment, the water is evaporated and the Dutch nibs dried in a roaster. The nibs are then treated in the same manner as nibs for natural-process cocoas.
Bywaters gives the object of the Dutch process as follows: (1) To improve the flavor, (2) to improve the color, (3) to improve the solubility, and (4) to improve the digestibility. The proportion of cocoa that can be dissolved is less than 25 per cent, even after treatment. The treatment darkens the color. Zenlea states that natural cocoas have a pH value of 5.2 to 6.0; chocolate 5.1 to 6.2; "Dutched" cocoas have a pH of 6.0 to 7.5; and chocolate a pH 6.0 to 7.8. The reaction depends on the original pH of the nibs and the quantity and kind of alkali added.
Chocolate and cocoa contain some organic acids such as acetic and tartaric. The reaction of the cocoa determines the amount of soda that can be neutralized by the cocoa or chocolate in cooking. Less soda should be used with a Dutched cocoa in such products as cake and cookies in which soda is used, for the natural acidity of the cocoa has been lessened by the treatment.
Zenlea describes the following types of cocoas: (1) Semi-cocoas, not on the market in powder form, with 32 to 45 per cent fat content, and used for fine quality ice cream and icings. (2) High-quality cocoas containing 25 to 35 per cent fat. A higher fat content would prevent their preparation in powder form and a lower fat content causes loss of aromatic constituents. (3) Breakfast cocoas contain not less than 22 per cent cocoa butter. (4) Semi-dry cocoas contain 15 to 18 per cent fat and are used for malted-milk mixtures and other products in which with more fat there is difficulty in keeping the fat uniformly distributed, and with less fat the cocoa flavor is too strong. (5), (6), and (7) Dry, extra dry, and very dry cocoas contain 10 to 12, 8 to 9, and 6 1/2 to 7 3/4 per cent of fat, respectively. (8) Solvent extracted cocoas contain from 0.5 to 3.0 per cent fat and have practically no chocolate flavor. And (9) prepared cocoas, which are cocoa mixtures containing such materials as sugar, skim milk, and malt.
The less the fat content of the cocoa the more readily it absorbs moisture from the air and the greater its thickening power when combined with water.
Zenlea declares the ideal temperature and humidity for storing cocoa to be 60-70°F. and 50-65 relative humidity. Heat, vibration, and moisture cause cocoa to lump and lose its apparent color, which makes it more diffi-cult to mix, though its quality may not be damaged.
The use of chocolate and cocoa in cake. The factors influencing the color of chocolate cake may be listed as follows. (1) Reaction. This is probably the most important factor in producing a red mahogany-colored chocolate cake, the cakes having this color usually having an alkaline reaction. Grewe states that the "color constituent of chocolate is yellow at pH 5 and changes to red at pH 7.5," but she does not state what this color constituent is.
Schaal states that whenever the pH of the finished cake is above 7.9, the soda taste is pronounced and objectionable. He recommends that hot water and soda should not be mixed nor the soda combined with the chocolate and hot water, for leavening gas is lost and the cake color is a too "foxy" red. The soda, he says, may be creamed with the shortening and cocoa, or it may be dissolved in the cold milk. In addition, the soda may be mixed with the flour.
Chocolate has a slight acidity which will neutralize a small amount of soda, but many chocolate cake recipes call for an excess of soda, which gives an alkaline reaction. As the excess is increased, the soapy, bitter, alkaline flavor of the soda becomes more evident. Sweet milk and soda are likely to impart a deeper red or mahogany shade than sour milk and soda, for the acidity of the sour milk neutralizes a part or all of the alkalinity of the soda, the extent depending upon the amount of soda used. The use of soda, whether enough is used to give an alkaline reaction or not, always darkens the color; a lighter shade is obtained with baking powder. This darkening is probably due to the tannin constituents, for similar results are obtained with molasses or sorghum in gingerbread, the shade being darker with soda and lighter when baking powder is used.