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
The Science of Fudge: How Fudge Is Made
Fudge is made by heating sugar and water to a temperature above the boiling point for water, which is 212° Fahrenheit. The candy maker pours the syrup into a pan so it can cool faster. This technique helps prevent sucrose molecules from forming into a large crystal.
How is fudge a supersaturated solution? ›
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.
What is the softball test when making fudge? ›
According to most recipes, the ingredients of fudge are cooked to what is termed in kitchen parlance the soft ball stage, that point between 234 and 240 °F (112 and 115 °C) at which a small ball of the candy dropped in ice water neither disintegrates nor flattens when picked up with the fingers.
What is done when fudge is cooked to avoid a grainy texture from improper crystallization? ›
Once a seed crystal forms, it grows bigger and bigger as the fudge cools. A lot of big crystals in fudge makes it grainy. By letting the fudge cool without stirring, you avoid creating seed crystals. Stirring would help sucrose molecules "find" one another and start forming crystals.
What gives fudge its texture? ›
The main difference is the texture, which is determined by two things: the size of the sugar crystals in the candy, and the concentration of the sugar. Toffee is smooth with no sugar crystals, whereas fudge has tiny crystals that give it that texture.
How does temperature affect fudge? ›
Confectionery experiments have shown that the ideal cooking temperature for fudge is around 114 to 115 °C (237 to 239 °F). The cooking is intended to evaporate a part of the liquid and concentrate the sugar. The temperature of the cream/sugar mixture (called syrup) rises as water evaporates.
How are crystals reduced in the making of fudge? ›
For instance, if you want to make rock candy, you need to let the syrup slowly cool down over many days until big sugar crystals form. But if you want to produce fudge, you need to continuously stir the syrup after an initial cooling period, so when the sugar crystals form, they stay small and do not grow too much.
What makes fudge firmer? ›
The amount of time you cook fudge directly affects its firmness. Too little time and the water won't evaporate, causing the fudge to be soft. Conversely, cook it too long and fudge won't contain enough water, making it hard with a dry, crumbly texture.
Why is the sugar not dissolving in my fudge? ›
It might be that you haven't dissolved all the sugar before boiling the fudge mixture. It could be that there just wasn't enough fluid or fat to enable the sugar to dissolve or it might even be that the fudge wasn't beaten long enough or hard enough.
How do you know when fudge is beaten enough? ›
After letting the fudge cool, it's time to beat it. It is important to stir constantly with a wooden spoon until the mixture starts to thicken and its surface starts to look dull or matte. Now is the time to stop beating and pour the fudge into a mould.
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 won't my fudge reach the soft ball stage? ›
The fudge needs to be cooked at a vigorous boil and needs to get to a minimum of 116C/240F, so you may need to increase the heat slightly. This is the soft ball stage and if you drop a little of the mixture into a glass of cold water then it should form a firm ball that you can still squeeze between your fingers.
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.
Why is my old fashioned fudge not hardening? ›
Fudge usually behaves this way when it's not cooked to a high enough temperature (due to oversight or a faulty candy thermometer).
What to do with failed fudge? ›
Options for what you can do with your unset fudge:
OPTION 1) Depending on how runny it is, you can either use it as a frosting for cakes, or a sauce for ice-cream. OPTION 2) Freeze it overnight. Cut it into squares. Cover each square thickly in melted chocolate, ensuring no part of the fudge is exposed.
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.
