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.

-Gritty
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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54 Responses to The Science of Fudge

  1. Steph December 26, 2011 at 4:36 am #

    As someone who loves making fudge and other kinds of confection, I appreciate your breakdown of the why’s/how’s of the process. Thanks dude!

    • Ashleen December 26, 2011 at 10:28 am #

      You’re welcome! I hope to try some of your delicious confections :)

  2. Crystal August 10, 2012 at 12:36 pm #

    I appreciate your part about the fudge being likely overcooked… I keep getting to the stir stage and it is already too thick at 110…. so I’m going to buy a new thermometer and a taller pot. Any other suggestions welcome! It is never grainy, and tastes good, but it rather like taffy when I go to stir upon cool down, and then cools to a firm texture, but yet melts in mouth.

    • Ashleen September 3, 2012 at 9:23 pm #

      Hi Crystal,

      How did it go with a new thermometer? It can be tricky, but I’m sure you’ll get it :)

  3. Dan December 20, 2012 at 5:13 pm #

    Wow!
    I helped my mother-in-law make fudge for the holidays, and being science oriented had all sorts of questions as to why stuff happened or didn’t (felt like a 3 year old asking Why? Why?) ! I feel like I just had fudge making explained to me by Bill Nye the Science Guy! Thanks! Now if you could just explain why it seems to super-heat when she adds extract? An obvious chemical reaction but what’s the science behind it?
    Thanks,
    Dan

    • Ruth February 25, 2013 at 7:30 am #

      You mean why does the vanilla extract boil like crazy when you pour it in?

      It is because the boiling point of sugar water is much hotter than the boiling point of alcohol (assuming your extract is in alcohol, but the same applies to plain water). When you put the extract in, the sugar water is still hotter than the boiling point of the extract — which causes the extract to evaporate like crazy.

  4. Kiara May 1, 2013 at 12:02 pm #

    So I am doing a science project with fudge so thanks for u r website

    • daisy December 3, 2014 at 2:06 pm #

      I am doing a science fair project on how fudge crystallizes in different tempers
      so your website is vary helpful thank you

  5. Andrew September 5, 2013 at 6:00 am #

    WOW tasted sooooo awesome thanks for the Crystal Fudge

    • leslie April 22, 2014 at 10:16 am #

      it was really good

  6. Andrew September 19, 2013 at 5:58 am #

    OMF it tasted sooo good thanks for this project :)

  7. Michelle Fowler September 23, 2013 at 3:32 pm #

    I need to know how my son would site this page as a resource for his science project

  8. N'Jernaria October 22, 2013 at 11:31 am #

    Yall motherfuckers supposed to help me out shidd

  9. Adaira November 7, 2013 at 5:30 am #

    hey im doing a project and i need citation for this website and i was wondering who the author was, thanks.

  10. Timothy December 15, 2013 at 3:27 am #

    I was using Ice water to check for the soft ball stage and it set up, I poured it onto a marble slab and added butter (1/2″ cubes over the top of it as my recipe said) waited for it to cool and folded in the walnuts, butter and vanilla. The “fudge” is still goopy…

    my recipe was:
    4 cups granulated sugar
    1-2/3 cups 4% whole milk
    1/2 cup light corn syrup
    5 – Dashes of salt from the shaker (salt is in the butter too)
    7-ounces unsweetened Bakers chocolate
    2 teaspoons vanilla extract
    4 tablespoons salted butter
    2 cups walnut halves, coarsely chopped

    I was watching the temperature pretty closely as the batch I did yesterday became solid very fast – I had strred it constantly as it cooked…

    Can I reheat it now that it has the butter and nuts in it or do I just use it like chocolate dip or something? (I’m reheating it now in hopes I can)

  11. Sara December 17, 2013 at 12:17 pm #

    This helped me so much with my science experiment. I wish I found this first. this would of saved all the mindless hours of searching for extra research.

  12. Denise December 27, 2013 at 11:24 am #

    Good presentation but, as i am a chemist, your molecular structure drawing is painful to look at. The correct way to draw the structure is to include the oxygens as a “O” . Each unidentified corner is assumed to be a Carbon. What you have drawn is cyclopenta-cylohexane. If you can get that in the kitchen with a 234 heat you are up for a Noble Prize. I assume you copied this from some non chemistry source. Please fix the structure or move Chemistry forward and get your Nobel Prize. No need to post this.

    • Anonymous March 17, 2014 at 10:58 am #

      Do you normally go on cooking websites and harass people about being chemists? It’s fudge, literally no one cares at all. Go to a Science or Chemistry forum and have people a million times smarter than you do what you just did, but about serious subjects.

      Just saying.

      • Larissa December 11, 2014 at 4:33 pm #

        Do you normally comment on peoples posts and harass people for trying to help? She was perfectly nice about correcting the author. There’s no need to be rude about it…

        Just saying.

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  17. Phil March 27, 2014 at 5:47 am #

    As a diabetic I’m not supposed to eat a lot of sucrose. However, because of its lower glycemic index I could eat a bit more of fudge made with fructose. But it definitely doesn’t work the same as sucrose! It seems like it skips the fudge stage and goes directly to taffy. are there modifications to the procedure and/or ingredients that would allow me to use pure fructose?.

  18. Denise April 19, 2014 at 3:03 pm #

    I’m curious if brown rice malt syrup could be used in place of corn syrup in fudge or other candy making. I tried a batch of fudge with the brown rice malt syrup, and it came out a bit grainy. However, after reading your troubleshooting tips, it could just have easily been that the cool down temp was listed at 150 degrees in my recipe, while you say 110 degrees. So now I’m not sure if it was the syrup or the temperature!

  19. CJ May 14, 2014 at 8:28 pm #

    WOW!

    Nice blog post, but I’m so glad I’ve been making fudge for years and years, because if I’d read this first (and the many comments after), I would never have attempted fudge.

    I have NEVER used a thermometer. I do mine by 1) times in my recipe, 2) consistency of sugar called for in the recipe (soft or hard ball), which I test for using cold water in a glass container, and 3) feel. It took a couple of tries at first, but in my 30 years of making fudge, I have only had 1 batch end up as a fail according to my standards. It was gooey, but I didn’t have the money or time to replace it and it still tasted good, so I used it anyway, and it got raves.

    I almost had another fail when it got hard and crumbly too fast, but my roommate at the time, had some experience with it, and she dashed to the frig, and poured a small bit of milk in my mixture and said, “Stir.” So stir I did, and she watched and poured a little more while I continued to stir, and voilà… my fudge was saved. I’ve used that little trick on my own more than once, and it’s worked with every kind of fudge I’ve made.

    Also, I’ve always used a wooden spoon. I wasn’t told why, but that’s how I was taught. I just found a site that said this, “For safety, use a long-handled wooden spoon that won’t heat up during the prolonged cooking period.”

    Finally, I didn’t see it mentioned anywhere, but I always store fudge in a cookie tin. Not plastic, but an actual cookie tin… otherwise, the fudge gets hard. The only other way is to wrap it in tin foil and then store it.

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  21. faye May 18, 2014 at 8:22 am #

    when do i add my chocolate chips and flavorings… before it cools to 110F or after? I heard you are not supposed to stir it from the point it finishes boiling until the point it reaches 110F,…… so when do I add my vanilla and chocolate chips?

  22. Rhonda June 1, 2014 at 1:04 pm #

    Hi, I am curious how the science is affected when cooking fudge in the microwave. What are some tricks or important things to know when cooking fudge in the microwave. Thanks.

  23. Shirl June 8, 2014 at 12:13 pm #

    I make fruity fudges – guava, passion fruit etc. I use the pulp from the fruit. My guava and mango come out ok, but I always have problems getting my passion fruit fudge to get firm. I have tried taking it to a temperature of 250F and that helps sometimes. I feel that the acidity in the passion fruit may cause the problem. Can you help? I use recipe:
    3 c sugar, one 14.5 oz tin evaporated milk, 1/2 tsp salt, 1 tbsp. corn syrup 2/3 c passion fruit pulp (it’s more like juice than pulp).
    Hope you can help.

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  25. MeloDiva June 16, 2014 at 2:26 pm #

    I had an epic fudge fail for an order tpday and didnt know why. Thanks to this post ive figured out my problem. Thankyou!!!

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  27. Volante July 27, 2014 at 7:43 am #

    omg! this is awesome! so much helpful information as to what’s going wrong with my fudge. i’ve got friends who’re like i don’t have a problem with humidity etc, only to find out they’re not making *old fashioned* fudge but ones with chocolate bits & marshmallow. not that there’s anything wrong but i prefer less unknown ingredients in my cooking ;)
    ANYWAY!
    My Sister-in-Law gave me a link to this posting and once i read through i saw where many of my problems had laid. i’ve had 2 spectacular yummy fails. one ended up a marvelous chocolate orange fudge sauce and the other a chocolate peanutbutter mush. ;) makes for good sandwich spreads ;)
    i’m gonna print this out and keep with my fudge recipe so that i know what to look for when attempting ^_^

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  32. steve black October 23, 2014 at 8:06 pm #

    Mom made a fudge I loved, but I can’t find the recipe. It was firm and rather crisp, oot creamy. Any guidance out there?

  33. steve black October 23, 2014 at 8:09 pm #

    Mom made a fudge I loved, but the recipe is lost. It was firm and rather crisp, not creamy. Any guidance out there?

  34. Jenny November 11, 2014 at 1:37 pm #

    I gave been making fudge for a while now and have my share of tootsie roll type fudge. I decided one day to put it back in the pan with a little milk and rebook it. Well it worked. I have to say though mine can be a little grainy sometimes. But I have people that beg me this time of year to make them some for Christmas.

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  37. FailedFudgeGal November 20, 2014 at 3:26 am #

    Thank you so much for your fudge troubleshooting tips. Anybody who lives along the Gulf Coast, or other locales where ultra high humidity is the order of the day – even in winter – has experienced Failed Fudge Frustration. I have made more pans of chocolate soup than I care to admit. I have tried myriad variations of ingredients in an attempt to create the creamy chocolate confection we all crave, with sporadic success. Who knew that all I needed to do was raise the cooking temperature a bit above 234° to compensate for humidity. The question is: how much?

    Do you have any suggestion as to how much I should increase temp? Mom never used to attempt fudge-making above 70% as it would never set. But she also slavishly adhered to the 234° soft ball stage, without deviation. Any recommendations would be appreciated. It’s time for me to start making holiday gifts, despite Houston’s miserable humidity. Thanks!

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  39. Veronica (Australia) December 13, 2014 at 8:01 pm #

    Hi, Thank you for saving my fudge today.

    I used a candy thermometer that I had had for a while and it proved to be unreliable. The first batch of fudge turned out to be crumbly and more of a biscuit mixture than fudge . The second batch didn’t set. With your advice and that of a reputable international chef I salvaged my fudge.

    For those who are interested in how I did this …
    * I returned each batch of fudge to the stove (in separate saucepans of course)
    * added just enough water to make a saturated solution ,
    *liquefied the ‘fudge’
    *The crumbly fudge took a bit more effort. I let it sit in the water till most of the ‘fudge’ has returned to a liquid state. Eventually I strained it to remove the remainder of the grainy bits that were being difficult.
    *then started again from the stage where you let the fudge reach 114 degrees without stirring.

    I was amazed that it worked. The chef suggested using electric beaters to beat the fudge and this also worked.

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