There's a lot of physical chemistry involved in making old fashioned fudge. The recipe calls for combining and boiling milk, bitter chocolate or cocoa, and sugar together until the temperature of the syrup reaches 238 degrees F (114o C), pouring the seething mixture into a bowl, cooling to 115 degrees F (46 degrees C), and then beating until the surface shine disappears. If you don't follow the cautions in the recipe -- wash down the sides of the pan with a wet pastry brush or cover the pan for a few minutes early in the cooking process; don't scrape the pan; don't disturb the candy until it's cooled; don't let anything, even a speck of dust, fall into the cooling syrup -- you are very likely to wind up with a coarse, gritty mass instead of creamy fudge.
Sugar dissolves far less readily in cold liquids than in hot. There is no way that two cups of sugar will dissolve in a cup of milk at room temperature. Heating the sugar and milk mixture allows the milk to dissolve more and more sugar, and by the time the mixture is boiling, all the sugar is dissolved. The general principle is that at a particular temperature, a given solvent (in this case, milk) can dissolve only so much of a particular solute (sugar). When the milk has dissolved all the sugar it can hold, and there is still some undissolved sugar left, the mixture is said to be saturated. The higher the temperature, the more concentrated the saturated solution becomes.
Water (and milk) boil at 212 degrees F (100 degrees C) at sea level, but the sugar changes that. In general, a solid dissolved in a liquid makes it harder for the liquid molecules to escape. Consequently, the solution has to be hotter for the liquid molecules to get away at the same rate, and the boiling point rises.
In our fudge, the rise in boiling temperature is an exact function of the amount of sugar in the solution. Consequently, we can use the temperature of the boiling syrup to tell when enough water has boiled away to give the syrup the right ratio of sugar to water. For fudge and similar creamy candies, the syrup should boil at a temperature 26 degrees F (14 degrees C) hotter than the boiling point of plain water.
Some of the initial water in the syrup has now boiled away. Because the sugar couldn't dissolve completely until the mixture was near boiling, the syrup reaches saturation very soon after it starts to cool. If you've done everything right, however, sugar does not come back out of solution. Instead, the syrup continues to cool as a supersaturated solution. The solid phase -- in this case, sugar -- cannot start to crystallize without something to serve as a pattern, or nucleus. However, if a single sugar crystal is present, the syrup will start to crystallize, the crystals will grow steadily as the syrup continues to cool, and the result will be very grainy fudge.
This is why most fudge recipes require that the sides of the pot be washed down early in the cooking process, either with a wet pastry brush or by putting the lid on the pan for about three minutes to remove any sugar crystals clinging to the container walls. It is also why the recipes specify that the sides and bottom of the pan should not be scraped into the bowl where the candy is to cool. There is too much chance of scraping in a stray sugar crystal.
As the cooling syrup gets more and more supersaturated, its tendency to crystallize becomes even stronger. Even a speck of dust can start the process if all the candy contains is sugar, milk, and chocolate. Using more than one kind of sugar can counter this tendency. Most fudge recipes contain either corn syrup (which contains glucose instead of the sucrose of table sugar) or cream of tartar (which breaks sucrose into glucose and fructose). The different sugars tend to interfere with each other's crystallization and minimize the chance that the candy will crystallize too soon. They must be used in moderation, however -- too much and the fudge will remain a thick syrup forever!
The final stage is stirring the syrup when it is lukewarm to promote crystallization all at once throughout the candy. Disturbing (stirring) a very supersaturated solution causes many crystals to form at once. Because they compete with each other for the dissolved sugar, none can grow very large. The result is the proper creamy texture of fudge and the change in appearance from shiny (supercooled liquid) to dull (a mass of very tiny crystals).
FAQs
When making fudge, heat and acid work together to convert sucrose – basic white sugar – into its two components, glucose and fructose. When these sugars are present, they prevent sucrose from turning into big sugar crystals.
What is the principle of fudge? ›
Heating the sugar and milk mixture allows the milk to dissolve more and more sugar, and by the time the mixture is boiling, all the sugar is dissolved. The general principle is that at a particular temperature, a given solvent (in this case, milk) can dissolve only so much of a particular solute (sugar).
What is the composition of fudge? ›
fudge, creamy candy made with butter, sugar, milk, and usually chocolate, cooked together and beaten to a soft, smooth texture. Fudge may be thought of as having a consistency harder than that of fondant and softer than that of hard chocolate.
What gives fudge its texture? ›
Tiny microcrystals in fudge are what give it its firm texture. The crystals are small enough, however, that they don't feel grainy on your tongue, but smooth. While you ultimately want crystals to form, it's important that they don't form too early.
What is the secret to non-grainy fudge? ›
Brush the sides of the pan with a wet brush at the beginning of cooking to dissolve sugar crystals stuck to the sides. Never stir the mixture during cooking or sugar could crystallize again. The mixture may seize and become grainy. Use a candy thermometer or conduct a cold water test to check if the fudge is done.
Why does butter separate when making fudge? ›
Fudge is basically an emulsion between sugar, butter and milk. If the butter gets too hot, it can separate, causing the fudge to become oily on top. This is easy to prevent by monitoring the temperature with a candy thermometer, but separated fudge can also be fixed.
What makes fudge hard or soft? ›
If you don't heat your fudge to a high enough temperature, you'll end up with a soft product. And if you heat the mixture too much, your fudge may be harder than you'd like.
What is the interfering agent in fudge? ›
Corn syrup acts as an "interfering agent" in this and many other candy recipes. It contains long chains of glucose molecules that tend to keep the sucrose molecules in the candy syrup from crystallizing.
Why won't my fudge firm up? ›
The most common culprit behind unset fudge is inaccurate temperature control. If the sugar mixture hasn't reached the correct temperature, your fudge won't set. Ensure you use a reliable candy thermometer and follow temperature guidelines meticulously to achieve the desired consistency.
What is the function of butter in fudge? ›
Smaller crystals result in a smoother, creamier consistency in the finished fudge. Coarse grainy fudge results when large crystals are allowed to form. Butter is added in the final stages to add flavor and smoothness and inhibit large crystal formation.
Although fudge often contains chocolate, fudge is not the same as chocolate. Chocolate is a mix of cocoa solids, cocoa butter and sometimes sugar and other flavorings and is hard and brittle. Fudge is a mixture of sugar, dairy and flavorings that is cooked and cooled to form a smooth, semi-soft confection.
What consistency should fudge be before it sets? ›
The trick to good homemade fudge is to cook the ingredients to the right temperature to form a sugar syrup, and cool the mixture properly so the texture of the fudge turns out smooth and firm, but soft enough to cut.
Why is my 3 ingredient fudge not setting? ›
Why won't my 3 ingredient fudge set? This often happens when the condensed milk and chocolate chip mixture isn't hot enough to start. Everything must be completely melted before it is transferred to the pan to cool.
What makes fudge taste grainy? ›
Fudge usually behaves this way when it's not cooked to a high enough temperature (due to oversight or a faulty candy thermometer). If your fudge is tough, hard, or grainy, then you may have made one of several mistakes: You may have overcooked it, beaten it too long, or neglected to cool it to the proper temperature.
How is chocolate related to chemistry? ›
Immediately after harvest, the beans are piled under leaves and left to ferment for several days. Bacteria create the chemicals, called precursors, needed for the next step: roasting. The flavor you know as chocolate is formed during roasting by something chemists call the Maillard reaction.
What is the chemistry behind sweets? ›
In general, candy is made by dissolving sugar into water to create a solution. Granulated sugar, the most common type used in candy-making, is sucrose, a disaccharide molecule made up of glucose and fructose. When you force these two molecules to break apart, a very tasty reaction occurs: caramelization.
How is food related to chemistry? ›
Chemical substances can play an important role in food production and preservation. Food additives can, for example, prolong the shelf life of foods; others, such as colours, can make food more attractive. Flavourings are used to make food tastier.
What's chocolate and how does its chemistry inspire such cravings? ›
Chocolate is the richest natural source of theobromine, but coffee and tea contain some of it too. Theobromine chemically resembles caffeine and has a similar stimulating effect on our brains. The combination of theobromine and caffeine found in chocolate is believed to create the small lift we feel after eating it.
