So I had a kind of pie-making binge weekend, and in the process I ran out of sweetened condensed milk, since I made two batches of homemade caramel (in the microwave! It's SO easy--just mix it up, microwave until it's thick stirring every 3 minutes. Way easier than stovetop. But I digress) last week, and then two pies that had sweetened condensed milk in them, and I just plumb ran out. Unlike tomato sauce, it's not something I usually keep dozens of cans on hand.
But a friend of mine had mentioned that a mutual friend makes her own sweetened condensed milk, so I thought I'd see if I could make some myself, since I really wanted a key lime pie and the main ingredients are lime juice (I had that, weirdly) and sweetened condensed milk (sc milk, combined with any acid, turns into a gel, which is why it is the foundation of many pies, including my favorite: cherry cream) and I had no car. (Also, I realized that easter candy season is upon us, and my cream candy filling recipe is based on sweetened condensed milk).
I emailed my friend for her recipe and found my mom's old homemade sweetened condensed milk recipe (on the back of her caramel recipe, of course). I looked some up online and found a thousand variations. My friend's recipe is:
Sweetened Condensed Milk
1 c. hot tap water
2 c. sugar
4 c. dry milk powder
1/4 c. melted margarine
Put hot water into the blender. Add the sugar, dry milk powder and melted margarine. Put the lid on the blender whirl it around for a full minute. The mixture will be kind of thin, but will thicken up after standing for about an hour. Store in frig or freeze. Makes about 4 cups = 3 cans condensed milk.
So I tried making powdered-milk-based sweetened condensed milk. It worked! Unfortunately, I could still taste the powdered milk flavor, even through the lime flavor in the pie, and I'm not a fan of powdered milk flavor, to put it mildly.
So then I remembered that I had seen a lot of recipes where you actually condense the milk on the stove as I had been prowling around the web looking for powdered milk based recipes. But milk is expensive. So I spent an hour doing a little math and calculated the cost of making sweetened condensed milk using two other recipes I found vs just buying a can.
Buying a can of sweetened condensed milk at WalMart in Longmont costs $1.68 a can, or $1.34 a cup (1 can is about 1 1/4 cups even though it's 14 oz--it's oz weight, not oz volume in a sweetened condensed milk can, and, unlike with tomato sauce, they aren't equal). And they're often out, so you might have to buy it somewhere else in town where it costs significantly more.
The easiest looking recipe I found, which I haven't tried yet, is to take a can of evaporated milk, stir in 1 1/2 cups of sugar, and heat it until the sugar is dissolved and it's "thickened" (whatever that means. I hate finding that word in recipes--HOW THICK does that mean, thickened? Drives me nuts.) This recipe costs $0.63 per cup because evaporated milk is that much cheaper than sweetened condensed, and sugar is cheap, too.
And the more complicated recipe that I liked was written up by a Malaysian lady. Of course I researched dozens of recipes and concluded that most were plagiarized from one original (although I couldn't tell which was the original)--and this on supposedly professional recipe sites. Embarrassing. Do they think they're the only site people look at and nobody will notice?
So of course I took a conglomerate of different recipes and tried it. I mixed up sugar and milk in the crock pot and cooked it until it had reduced by half, and it was still pretty thin but people on blogs and in comments had assured me it would thicken as it cooled, and it did but it was still kind of thin. But they all said it was thinner but worked fine in candy recipes and stuff. I also stirred in butter, like some recipes suggested, and that just floated to the top and solidified there as the milk cooled, so that was a fail. And I stirred in vanilla, which made a delicious flavor but not the pure sweetened condensed milk flavor I was looking for.
So we made rainbow fudge with it. Aside from the fact that it was far too sweet to be edible, the stuff never did set up. It was just as runny as could be. Obviously the too-thin sweetened condensed milk was not sufficient.
Back to the drawing board. I googled. I read comments on recipes that said stuff like "Mine didn't set up so I tried this...." And I made another batch in the crock pot.
Cooked it on high instead of low until it reduced by half. Cooking it on low (the first time round) took 16 hours to reduce by half. On high it only ("only") took 12. (You have to do it with the lid off or it doesn't reduce, by the way). But it was still far too thin. So I added baking soda, like some commenters swore worked. No good. Still too thin. Extra sugar did nothing. Frustrated, I poured the stuff out of the crock pot into a sauce pan and boiled the heck out of it.
While I was doing that, I realized something. Altitude. The recipe was written for Malaysia, on sea level. I'm at nearly 6000 feet. Boiling sugar at this altitude never works the same because the boiling temperature is different, so I have to make candy by the cold water test rather than by a candy thermometer temperature or it doesn't work.
I boiled it until I thought it was thick enough, and then put it in jars and refrigerated it over night. Success! Except I'd cooked it too long this time and had just hit the line between sweetened condensed milk and dulce de leche. SUPER delicious. Slightly overcooked. I made it into a key lime pie anyway. I really wanted one that didn't taste like powdered milk!
Anyway, that all got me thinking--of course I should look up dulce de leche recipes and see if they were any better than sweetened condensed milk recipes. Because sc milk is just undercooked dulce de leche. The ingredients are the same. And that was really, really helpful.
For one, the dulce de leche recipes reminded me what I knew and forgot--the thickness of the finished product is not based on cooking time but on cooking temperature when you're dealing with sugar, which is why a sea-level recipe won't work at high altitude in the crock pot to thicken, only to reduce.
So here's what worked up here in Colorado.
Sweetened Condensed Milk Recipe (DIY)
6 cups of whole milk (I hear skim milk doesn't work, but cream does--that would be amazing, but not cheaper)
2 cups sugar
1/4 tsp baking soda (totally optional--it browns if it you're into that kind of thing)
Stir all ingredients together in the crock pot and cook on high with the lid off until the mixture has reduced by half--about 12 hours. (I checked this with a skewer. I dipped it straight into the liquid when I started and then drew a line around the skewer at the liquid line. Then I measured with a ruler and drew another line around the skewer exactly half way down. When the liquid reached the lower line, it had reduced enough.) Pour the condensed liquid into a large sauce pan (use a really really big one, like a soup pot, because it climbs). Boiled it on medium and then low until it thickened enough. (You can test it by putting a little in a spoon and setting the spoon on an ice cube--when it cools to the right thickness, you've cooked it long enough.) I did NOT stir the whole time--after I turned it to low, I stirred just every 5 minutes or so to let the steam out. If you want dulce de leche, cook it until it's light brown and thicker. Pour it into glass jars, cover, and refrigerate. If it looks like there are hardened bits in it, pour it through a strainer into the jars.
This recipe cost only $0.43 per cup. And it made a little over 2 cans worth (about 2.5 - 3 cups). So it's definitely cheaper, and not very hard.
I'm not completely satisfied yet, of course. I need to try:
--cooking it on the stove the whole time (I hear it works but that it can require you to strain the milk at the end), for 2-4 hours total
--cooking it in a pan in the oven. I read you can use that to make dulce de leche, so I'm wondering if you can do sc milk that way, too
--boiling the milk and sugar together first and THEN putting it in the crock pot with the lid off, so the crock pot can maintain the higher temperature (it never did actually get to boiling when I started it cold, on low or on high)
--using the caramel method (microwaving it). It works for white sauce and caramel, so maybe sweetened condensed milk, too? Probably would have to reduce the milk first, though, on the stove or in the crock pot.
--trying it without the baking soda. Most recipes don't use it, and I suspect it's extra. Dulce de leche recipes say it's just to help it brown.
I liked using the crock pot because it was so gentle--it didn't burn or scald or otherwise ruin the milk. Nothing grainy or lumpy or needing straining. But it also didn't thicken it. Combining that with the stovetop worked fine.
Those might all fail, but at least I know now how to make both sweetened condensed milk and dulce de leche without a can.
(With a can, the best dulce de leche ever is made by boiling the can, unopened, for 2-4 hours. But you have to keep water over the can or it can explode. Tim exploded a can once doing this, so it really is not a myth.)