This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Fondant is made when sucrose is cooked with water to a definite temperature, the sirup is cooled and beaten, and the mass crystallizes. According to accepted standards for good fondant, it should be snowy white. The crystals should be so small that they are imperceptible and not gritty on the palate. The fondant should be soft enough to be plastic and velvety but not dry and crumbly.
Cooking of fondant. Enough water should be added to dissolve all the sugar during the cooking period. With rapid boiling a larger proportion of water can be used. With a slow fire and slow boiling, it is preferable to use less water, or a long time is required for the cooking process. With larger quantities of sugar the proportion of water is reduced because evaporation is relatively more rapid from the small quantity of sirup. Covering the pan during the first part of the cooking period allows the steam to dissolve and wash down crystals from the sides of the pan.
Some directions state not to stir the sirup while it is boiling. It is well to stir it to be sure all the sugar is dissolved, so that there are no crystals in the sirup to start crystallization while it is cooling. The danger in stirring candy while it is boiling comes from splashing the sirup on the sides of the pan. These drops of sirup on the side of the pan become dry and nuclei form which serve as a basis for crystallization while the sirup is cooling. A damp cloth is often used to swab the sides of the pan to prevent nuclei and crystals forming there during the cooking of the sirup. Since boiling solutions of sugars are not saturated solutions, any candy can be stirred as much as desired while it is boiling without causing crystallization, provided the sirup is not splashed on the sides of the pan. But after the sirup stops boiling it cools quickly and soon reaches the super-saturation point. If the sirup is poured for cooling from the pan in which it is cooked, it should be done quickly. Directions often state not to scrape the portion clinging to the pan with the spoon. Of course this is because the small amount of sirup left on the sides of the pan soon cools to the supersaturation point, and if it is stirred, as it must be in scraping it from the sides of the pan, crystals may form that will seed the entire mass. The thermometer should not be allowed to roll around in the sirup while the sirup is cooling for this agitates the sirup. The pan should be set level so that all parts of the sirup cool equally. The container in which the fondant is poured to cool should have a smooth surface, as rough surfaces may induce crystallization.
In the preceding pages the factors determining the size of crystals in sugar crystallization are discussed. These factors are applicable in making fondant and fudge.
Concentration and temperature for cooking the sirup. A sucrose solution containing 80 per cent of sucrose, i.e., 80 grams of sucrose and 20 grams of water, boils at 112°C, is saturated at 90°C. and super-saturated below 90°C. Therefore, no crystals are formed in a sucrose solution cooked to 112°C. until the temperature drops below 90°C. Woodruff and van Gilder found that fondant cooked to 115°C. has an average water content of about 13 per cent. The higher the temperature to which the sirup is cooked, the less the percentage of water in the fondant. If fondant contains too small a proportion of water, it is dry and crumbly; if too much, it is sirupy and runny. When the sirup is cooked to 109° to 111°C. (Experiment 7B), the fondant contains a high percentage of moisture. Sirups cooked to this temperature give a fondant too fluid to knead or mold, unless it is beaten when hot. Fondant sirup for ordinary home use may be cooked from 113° to 115°C. The lower temperature gives a softer fondant for remelting and making candy like peppermints; the higher temperature gives a drier fondant for molding. It should be
Fig. 1. - Crystals from fondant. The sirup was cooked to 113°C.-then beaten immediately until the mass was stiff enough to knead. Magnification approximately x 200.
Fig. 2. - Crystals from fondant. A portion of the same sirup as that in Fig. 1. It was beaten slightly while hot to start crystallization; then left to stand several hours until the whole mass was crystallized. Magnification approximately x 200. (Photomicrographs of sugar crystals by courtesy of Ethel L. Swanson.)
Fig. 3. - Crystals from fondant. A portion of the same sirup as that shown in Fig. 1. Cooled to 40°C. Then beaten until the mass was stiff and kneadable. Magnification approximately x 200.
Fig. 4. - Crystals from fondant. A portion of the fondant shown in Fig. 3, immediately after adding 6 per cent of beaten egg white. Magnification approximately x 200.
Fig. 5. - Crystals from fondant. A portion of the same fondant shown in Fig. 3 after 20 days' storage. Note aggregation of the crystals. Magnification approximately x 200.
Fig. 6. - Crystals from fondant to which 6 per cent egg white v as added after 20 days' storage. Compare with Fig. 4. Magnification approximately x 200.
Fig. 7. - Crystals from fondant. A portion of the same fondant shown in Fig. 3 after storage for 40 days. Note the growth of crystals. Magnification approximately x 200.
Fig. 8. - Crystals from fondant, with 6 per cent of added egg white after 40 days' storage. A comparison with crystals in Fig. 4 and Fig. 7 shows that egg white tends to retard crystal growth during storage. Magnification approximately x 200.