Dr. Kiki Sanford goes over the chemistry of fudge to explain how super saturation and crystallization are involved in making delicious fudge.
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Dr. Kiki Sanford: Hi, I am Dr. Kiki and you are watching Food Science. Today we are going to learn all about the chemistry behind making fudge. That's right, I said chemistry behind fudge, turns out that fudge is very special in the candy world. Its recipe is based on the chemical principles of super saturation and crystallization. To start making fudge, what you need to do is take heavy cream with chocolate, some sugar, and a little bit of salt. So, I am going to start out putting one cup of heavy cream in this sauce pan. I turn the temperature on low and add four ounces of chocolate. I am going to melt this chocolate into the cream before adding any of the other ingredients. We are just going to sit here and I am going to stir this. The chocolate is starting to melt on the bottom of the pan I can feel it, so now the chocolate is fully melted into my cream and I am going to add my sugar. I am going to add two cups of sugar, which is way more than cream, should normally be able to dissolve. I am also using super fine granulated sugar, so that it will break down a lot easily and will be able to dissolve it into here. I am going to add a pinch of salt, and I am also going to add a tablespoon of Karo Syrup. Karo syrup is corn syrup; it's made up of glucose molecules, which is different from the table sugar. Table sugar is made up of sucrose. What ends up happening as you mix this altogether is that the sucrose and the glucose compete with each other and kind of messes up the crystallization process. So that crystals don't form earlier than you want them to. We're going to keep increasing the temperature of the solution until it is boiling, and we want it to reach well beyond the normal boiling temperature of milk, so we have reached our boiling temperature, it's 234 Degrees Fahrenheit, and what's happened right now is the fudge is boiling furiously. This means that all of the sugar has been completely dissolved into our milk and chocolate solution. So we know that we have a completely super saturated solution at this point so we can move on. What I was doing just a second ago is wiping down the sides of my sauce pan to make sure that there aren't any stray sugar grains hiding around. One of the problems with the cooling process is that, now that this syrup is supersaturated. It really wants to crystallize. The sugar doesn't want to be a liquid; it wants to be a solid. So it really wants to crystallize, but we are not going to let it. I am going to take this, pour it into a cooling container. Now that we have taken it away from the heat, we are going to put it into a quiet place. We are not going to agitate it. We are not going to stir it anymore. We are just going to let it cool on its own, so I am going to cover this fudge with a nice piece of cheesecloth, that's going to help keep any bits of dust or other debris from falling on our fudge as we let it cool. It is going to cool for a long time. So now I have waited a couple of hours for my fudge to cool down. I haven't been agitating it. Well maybe a little, I stuck a thermometer in it, so I could find out exactly how cool it was getting. Now let's take a look at it. I had this cloth over to make sure that no stray dust particles got in to keep it as clean as possible. It looks really good; I have got a nice shiny top on my fudge. It looks like it hasn't started to crystallize at all. This is great. But now we are at just the right temperature, what we are going to do is I am going to add a little bit of butter, two tablespoons of butter to the top of the mix here, and a teaspoon of vanilla. There is something about the combination of vanilla and chocolate that really makes the chocolate pop. So now I am going to go back and grab my spoon from earlier and take out my thermometer, and just start stirring. I have waited to this perfect temperature, I am mixing like crazy, my butter is going to melt, and right now it's got a nice shiny sheen on it, and this is going to stay for qui
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