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I've seen two basic kinds of recipes for peanut butter fudge. One is the traditional method of making fudge where sugar and milk is boiled and then peanut butter is added. The other method involves mixing butter and peanut butter over heat, usually until it boils, then mixing in powdered sugar off heat.
I understand the need to bring the sugar and milk mixture to a boil in the first method, as it is necessary for the sugar to candy. But is the step of heating the peanut butter and butter in the second method only to make mixing easier? Would the end result be any different if instead of heating the peanut butter and butter, you just stirred in room temperature butter to the peanut butter and did an extremely thorough job stirring everything together?

Here is an example of the second method that I'm wondering about: https://preppykitchen.com/peanut-butter-fudge/

3 cups powdered sugar 360g, sifted
1 cup peanut butter 250g, smooth or chunky
1 cup unsalted butter 226g
2 tsp vanilla extract 10mL
1/4 tsp salt optional

1. Line an eight inch square dish with foil or parchment paper.
2. Add the butter and peanut butter to a medium pot then place over medium heat and bring to a boil stirring occasionally.
3. Bring to a steady boil then remove from heat and stir in the powdered sugar and vanilla.
4. Once the sugar is completely stirred in transfer to your prepared dish and smooth with a spatula. Set aside to cool and set (about an hour).
5. When the fudge has set you can invert onto a cutting board, remove lining and cut into squares.

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  • There are many in-depth sources of how to properly control the temperature and agitation in candymaking in order to make fudge. I have never come across your second method, so I won't write an answer, but you might be interesting in reading articles like this one: blog.thermoworks.com/candy-chocolate/… for a background.
    – rumtscho
    Aug 16 at 11:34

1 Answer 1

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I referred to this page from Pastry Chef Online on the science of making fudge.

Fudge happens when you heat sugar and mix it with other ingredients. The water evaporates and leaves a sugar concentration that crystallizes. See footnote about sugar's water content.

So, if you just stirred in the powdered sugar, you wouldn't be evaporating the water in the sugar, the sugar wouldn't concentrate, and the end result wouldn't crystallize and turn into fudge.

Footnote - sugar contains some water.

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  • Are you saying that you need to evaporate the water from sugar crystals or they won’t crystallize?
    – Sneftel
    Aug 16 at 7:16
  • In the second method, would mixing the powdered sugar into the hot peanut butter off heat be enough to evaporate the water in the powdered sugar and crystalize?
    – Edward45
    Aug 16 at 11:16
  • @Sneftel I believe that's correct. The water needs to evaporate to create a supersaturated solution so that the sugar will crystallize. Here's a site with the science explained - foodcrumbles.com/how-to-make-fudge-controlling-crystallization
    – JC007B
    Aug 16 at 11:31
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    The water you suggested being present in sugar is negligible . The point in candy making is not to evaporate the water, it is to get the sugar to the target temperature, which should be 112 C for fudge. If you would start with a dry method and heat until the exact point where that 1% of water from your footnote has gone, but don't heat it to the candying temperature, you won't get fudge. If you are seeing references to evaporating somewhere else, they refer to the wet method of sugar work, where you add significant amounts of water, and then evaporate them before waiting for the temp.
    – rumtscho
    Aug 16 at 11:31
  • @Edward45 I would assume so since that's how the recipe is written and the boiling point is 212F/100C - the residual heat seems to be enough to melt the sugar.
    – JC007B
    Aug 16 at 11:35

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