Fudge was actually one of my first escapades into the 'essences' of cooking. There are so many different recipes and methods out there, I just wanted to know what made fudge fudge, as opposed to something else.
So, here's my definition: fudge is a solution of sugar and liquid, which is boiled until it reaches a certain saturation, and then crystallised into a solid. All that means is, you can mix any amount of sugar with any amount of (primarily water-based) liquid, and cook it until a certain amount of the liquid has boiled off, and it will set into fudge when it cools down. More or less, anyway.
When you mix sugar with water (or a water-based liquid like milk, cream, apple juice), it dissolves - that basically means the bits of sugar go into the gaps between the 'bits' of water, until it's invisible and not taking up extra space. If it helps, imagine a box of footballs (those are the bits of water), and then me throwing a box of oranges (the bits of sugar) into that box. The oranges just snuggle into the gaps between the footballs. The level the footballs reach in the box doesn't increase, because the oranges don't need any extra volume to be able to fit in. I apologise if you have a degree in chemistry and you're currently having a heart attack - I'm basing this almost entirely on a science lesson I had when I was about 13, so if it's horrifically inaccurate, please forgive me. The fact is, this analogy works for me, and it pretty much works for fudge. In fact, you don't really need it at all to understand fudge, but I thought I'd add it in because I thought of it and I think it's a nice description of dissolving.
So imagine I'm now heating up this box of footballs (bear with me). In the world of particles, that means the footballs are going to start jumping around. The overall result of this is they end up moving further apart. They're bouncing around so much that they can't be snuggled as close together as they were when they were cold. Another result of heating it up is that some of the footballs jump around so much they jump clean out of the box and fly away. This is, essentially, boiling.
The footballs are jumping around all over the place, spread out nice and far from each other, and quite a few of them have jumped out now. So many, in fact, that if we suddenly cooled it down (stopped them all from jumping around), there'd be so many oranges, they wouldn't all fit into the gaps between the footballs. Some of them would be taking up extra space of their own because there are no more gaps for them to fit into. This is what's known as a saturated solution - it just means all the gaps are full of oranges (or solute, if you want to be scientific).
Actually, we are going to cool it down now. We're gonna stop it from boiling and let it cool down so everything stops jumping around. Now we have to remember the other thing that happened - the footballs moved apart. As they cool, they move closer together again. But there are so many oranges around, they stick in all the gaps as the footballs move together, and everything is packed so hard together that it goes completely solid. It's now crystallised.
Depending on how many footballs we lost before we cooled it down, it will have a different texture when crystallised. If we only lost a couple, it would still be runny, but it would just be thick, like a syrup. If we lost nearly all of them, it would be really hard and brittle, almost toffee. If we lost just the right amount, it will be slightly soft, a little bit crumbly and wonderfully delicious - you guessed it, fudge.
The next question that arises is how do we know when we've lost just the right number of footballs. Well, unfortunately, I don't have a bit of the analogy for this, so you might have to take me on trust. If you happen to have a chemistry degree and you can think of a way to add to my analogy for this explanation, then feel free to contact me! The thing is, as the footballs boil and the mixture becomes more saturated (a higher concentration of oranges compared to footballs), the solution needs to be hotter in order to be boiling. Something about the amount of oranges makes the footballs more reluctant to jump out, and we have to make it all even hotter to keep it boiling. This is a bit strange, but luckily, has good implications for fudge makers. It means that we can tell exactly how concentrated the sugar solution is, by doing nothing except taking it's temperature.
And it just so happens that the temperature at which the syrup is exactly the right concentration that it will become fudge when it crystallises is.....
So all we need to do to make fudge is get some sugar and some water-ish liquid, boil it until it's about the right temperature, and let it set and then BAM - fudge! It's really that simple (yeah I said simple, stop laughing at my footballs-and-oranges analogy).
Link to Part 2
Link to Part 2