Monday, November 20, 2023

Coffee Icing: or, Fun with percolators

I made these as an excuse to use the percolator.

Coffee Icing
1½ cups granulated sugar
¾ cups strong black coffee
1 tsp butter

Cook coffee and sugar until they form a soft ball when tested in cold water (about 240°F with a candy thermometer). Drop the butter on top without stirring it in. Then allow to cool until lukewarm.
Beat the mixture until it thickens and lightens in color. Quickly spread onto the cake (it sets very fast).
This is very good on spice cakes.

Note: The original recipe was for fudge icing. If you want to make it as written, stir three tablespoons of cocoa powder into the sugar before you begin (eliminating any lumps), and use milk instead of coffee.

Source: A Book of Selected Recipes, Mrs. George O. Thurn, 1934

A Book of Selected Recipes, Mrs. George O. Thurn, 1934

I don't like coffee, but I just find percolators so entertaining in their own understated way. And so, I wanted an excuse to use the one I have lying around the house. First, we revisited Mrs. George O Thurn's mocha cake. I have let that recipe lie dormant for too long. Good recipes should not be pressed into the pages of a book, they should be splattered with errant eggs.


But that was only one batch of coffee. And obviously, we can't drink quarts of iced coffee just as an excuse to operate the percolator again. You may think I'm daft just because I love the burbling sounds of this thing, and seeing the water splash up in the glass knob in the lid and gradually get darker. Also, it looks like an 1800s silver teapot with a power cord coming out the back. As things get tougher and tougher, sometimes it's nice to take pleasure in the little things without worrying about how silly you look. 

Anyway, we've made a few attempts at boiled icing, and I thought that today was the perfect day to try making it with coffee. If it came out right, it would be like topping a cake with a delicious cup of iced coffee made to A Book of Cookrye standards. As a reminder, a cup of coffee in my happy world looks like this:


I took a boiled fudge icing recipe from Mrs. George O. Thurn's book. At first I was like "Why does she have six recipes for boiled icing?" But actually, having six icing recipes allowed us to pick the one that matched what ingredients we had on hand. Five of them used egg whites, and I didn't want to waste egg yolks. One called for heavy cream, which never buy unless I have specific plans for it. And so, only one recipe remained to suit my percolator-related needs.

And so, we took Mrs. George O. Thurn's recipe for fudge icing,  omitted the cocoa powder, and replaced the milk with coffee. As an aside, boiled icings use a lot of sugar. Just like the last time we dabbled in boiled icing, we are putting more sugar on top of the cake than we put in it.

In other words, after adding the coffee to the pot, I could have either made a batch of icing or drunk this as-is. I should note that I reduced the recipe to two-thirds its original quantity because I couldn't imagine putting nearly a pound of sugar on top of a small square cake- even though I only made the cake as a vehicle for said icing. Even after getting out the tiniest thing that was stovetop-safe, we barely had enough coffee to coat the bottom of it.

For the longest time, nothing happened in the pot. I began to wonder if the stove was defective or something. (I have a bit of a combative history with flat-top stoves.) But after a long time, the coffee boiled up so much that I wished I'd used a bigger pot.

This mixture took a surprisingly long time to reach the soft-ball stage.  I began to wonder if the milk used in the original recipe was crucial to making this icing work. But eventually, after a lot of stirring, the icing formed a soft ball when tried in iced water. And so, we set aside our syrup to cool down to nearly room temperature. I would have forgotten to add the butter had I not measured it out at the beginning and left it conspicuously waiting right in front of me.

And so, we left the coffee syrup out to cool, just as we did when we made Louise Bennett Weaver's spice cake. Then came the long beating. And I do mean the long beating. I must have spent a solid fifteen minutes with a wooden spoon before seeing anything different in the pot. I began to wonder if I needed to return it to the stove for further boiling. Then, at long last, we began to see the slightest suspicion of a color change. After beating the snot out of the icing for still longer, it finally lightened to about the color of peanut butter.

I've seen a lot of candy instructions that say "beat until it loses its gloss," and decided that made sense for today's icing. We were again bitterly reminded of (what apparently is) a fundamental truth of boiled icing. You may have to beat the icing for half an eternity, but once it's ready you have at most 45 seconds to hastily smear it onto the cake. As you can see, I was not fast enough.

Indeed, while the icing had been obstinately runny for a long time, it completely solidified onto the pot while I hastily tried to scrape it out and smear it onto the cake.

However, an easy solution to our icing ineptitude was at hand: the presentation platter! We could cut away and conceal all the unsightly edges, even if it meant no one (besides those who did the baking) got a corner piece.

The cake, of course, was fine. But I was more concerned with the icing on top..... which was absolutely delicious. You may think that boiling coffee for so long would ruin it, but it was just fine.

Imagine a cake topped with coffee-flavored fudge on top, because that's what we got. I would definitely make it again. However, in the future, you shouldn't beat it too firm. As soon as it barely begins to lose its gloss, get it onto the cake- and fast. I wouldn't try to use boiled icing to cover a layer cake. The icing would probably set in the saucepan before you were halfway done. But it's great for when you're serving a cake out of the pan, or for drizzle topping. 

Also, this kind of icing requires patience. But on the bright side, you may offset the calories with the arm workout that comes with making it.


  1. Coffee flavored fudge. Now I know what new item the cafeteria (and all the coffee shops) at work need to sell.

  2. Have you ever heard of ermine frosting? It’s another boiled icing and supposed to be good to serve to people who don’t like frosting.

    1. I've seen people suggest it for red velvet cakes, but I've never looked it up. I'll definitely have to, since a lot of my friends like a decorated birthday cake but then discreetly scrape the frosting onto their plates.

      PS- I love Discworld too!