The Science of Fudge

Fudge can be made from just a few ingredients: sugar, butter, and milk or cream. However, despite the simplicity of ingredients, fudge has a reputation for being quite difficult to make. This is because the creamy texture of fudge depends on the perfect amount of sugar crystallization. If there is too much crystallization, or the sugar crystals are too large, fudge will have a gritty texture and be too hard. Not enough crystallization, and it won’t be fudge, but rather a thick, syrupy goo. I’ve messed up fudge enough times now to realize that fudge failures can still taste nice (I’ve used my egg nog fudge failures to make egg nog lattes) but one of the most important features of fudge is its texture.

Making bad fudge isn’t such a terrible thing so if it doesn’t work for you right away, don’t give up! If you understand the process of fudge making (which you will by the time you finish reading this post), each failure is a learning process and a step towards making you a fudge master! Some fudge experts are so skilled that they can make fudge without a thermometer and will dip their fingers into boiling sugar. Yeahhh you won’t see me doing that any time soon.

Epic Fudge Fail

One of my friends, who also loves to bake, and I got together one day to attempt fudge. She shall remain anonymous, at her request. I, on the other hand, have no shame. Now, while most people mess up fudge through problems with sugar crystallization, we found a way to have an even more epic fail. We managed to melt–get this– not one but TWO DIFFERENT types of plastic into the fudge. Oh yes, we managed to do that. In our defence, however, I would like to point out that one of those plastic melt-downs was not our fault. My friend had bought a candy thermometer earlier that evening. I’m not sure if we had a faulty thermometer or if the problem was the brand of thermometer but, it decided to partially melt some type of plastic into the fudge. This led to my friend’s rage outburst: “Curse you PC [president’s choice]!! PC?! That must stand for piece of crap!” How I love her. I still have no idea what this plastic was doing in the thermometer but I checked the packaging and it did NOT say there was a piece of plastic that needed to be removed. I stand by what I said that this one wasn’t our fault. The other plastic, on the other hand, … well let’s just say… use a wooden spoon for fudge making.

I wouldn’t say that fudge is difficult to make, per se. Just very easy to mess up. When you do succeed,though, it feels good. After tasting our first delicious, smooth, and creamy fudge my friend and I began prancing around the kitchen saying things like “We are so good” or “We are the fudge masters.” I guess I spoke too soon because I had three successive failures afterwards. I blame faulty thermometers. I undercooked one batch, and then overcooked another, both of which are really easy to do if your thermometer is off. After learning this the hard way, I’ve decided to not rely on candy thermometers alone.

Testing Thermometers

I tested two different thermometers after beginning to get frustrated with fudge-making. I put a pot of water on the stove with the thermometers immersed in the water. I made sure that the thermometers were not touching the bottom of the pot, as this can give a false reading. When the water began to boil I checked the temperature. One thermometer said 90 C and the other one said 110 C. Since the boiling point of water is 100 C, I’m not very confident in either reading.

Cold Water Test

I’ve decided to start using the cold water test to double check that my thermometer is not really lying to me. Fudge needs to be cooked to the soft ball stage. I found this video on YouTube to help determine if you are at this stage.

Basic Steps in Fudge-Making

1. Dissolve sugar in liquid ingredients, and add corn syrup or acid to prevent big crystals from forming.
2. Cook mixture to the soft ball stage.
3. Allow mixture to cool, slowly.
4. Mix mixture to form small crystals.

The Science Of Sugar

Regular white sugar is also called sucrose. I got out my old Principles of Biochemistry textbook so I could draw a picture of what a sucrose molecule looks like.

or more simply represented as:

As you can see above, sucrose is made up of two other types of sugar (glucose and fructose.) Sucrose can be broken down into these two components when you add heat and an acid.

Sucrose has a tendency to crystallize when making fudge and other confections. This is because when you dissolve sugar in water, and then begin to cook this mixture, the water begins to evaporate. This leaves less water for the sugar to be dissolved in. The sucrose molecules do not like this, and decide to crystallize out of the sugar solution. Like I said earlier, a good fudge texture relies on the perfect balance of crystallization. You eventually want the sugar to crystallize to a certain extent, but you want the sucrose molecules to form little tiny crystals that are so small, you won’t be able to feel them in your mouth. If crystallization occurs too early in the fudge-making process, they will be big, gritty crystals. There are a few factors that affect sucrose crystallization. These factors can be manipulated to impede crystal formation so that you only get nice, tiny crystals.

  • Glucose and fructose
    Glucose and fructose molecules get in the way of sucrose crystallization. If enough glucose and fructose molecules are present, they surround the sucrose molecules, preventing too many sucrose molecules from joining up to make a big crystal. Remember that heat and acid will convert sucrose to its two components? By adding acid such as cream of tartar to a recipe, some of the sucrose will break down into glucose and fructose. To achieve a similar effect, you can also add corn syrup, which is made up of glucose.
  • Butter
    Butter plays a similar role in sucrose crystallization. Like glucose and fructose, butter gets in the way to control the number of sucrose molecules that can join to form a crystal.
  • Temperature, agitation, and seed crystals
    This should be a small refresher of high school chemistry. Allowing the fudge to cool slowly makes for a smooth texture. If cooled too quickly, if the fudge is agitated during cooling, or if seed crystals are present, this can start a chain reaction of sucrose molecules crystallizing out of the mixture. Here is a video from a chemistry class that I found on YouTube. It demonstrates this crystal chain reaction. Seed crystals are any particles that can set off the crystallization chain reaction. They can be sucrose crystals or any other surface that sucrose molecules would like to cling to.
Here is a picture of gritty non-fudge. It is gritty because I didn’t wait for it to cool before I mixed it. As a result, it has big sucrose crystals.


Fudge Troubleshooting

-Doubling the recipe
It is not a good idea to double or triple fudge recipes, unless you have some good equipment that will allow you to do so. By doubling the recipe, some parts of the sugar mixture may cook faster than others. So while some of the sugar is at the soft ball stage, others parts of the mixture may not have reached this stage yet (or be past it.)

-Too soft or runny
If you keep beating the fudge mixture and it just won’t turn into fudge, you likely undercooked it. Make sure you reach the soft ball stage.
Humidity also affects the crystallization. Sugar is attracted to moisture, so on a really humid day, some moisture from the air will be absorbed into your fudge. If there is too much moisture present, it will dissolve your sucrose crystals and not allow your fudge to set. If you in a humid area, you may need to cook your sugar a few degrees higher to make up for this.

-Too hard
If you let your fudge cool and go to mix it, but find you can’t, then you’ve overcooked your fudge.

This could be due to a variety of things:
Fudge did not cool to 110 F in pot before it was stirred.
Butter was added before the mixture reached a boil (and impeded the ability of the liquid to dissolve the sugar crystals.)
Mixture was stirred throughout boiling or during the cooling stage.
Fudge was cooled too quickly (i.e. in fridge)
Seed crystal formation on side of pot (try buttering the sides of the pot to prevent sugar from sticking.)
Not enough acid, corn syrup, or fat in recipe.

If there is one thing for you to take away from this post, it is this: small sugar crystals = good. Large, gritty crystals = bad.
I made some delicious, creamy egg nog fudge today, but in the interest of keeping this post from becoming a novel I will post the recipe tomorrow.

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