By Ross Goldenberg
May 5, 2011

In my house, Cinco de Mayo is a major holiday. This May Mexican fiesta celebrates God knows what (a military victory, maybe?) but around here it’s a throwback to my college days. As a 20-year-old at NYU, ordering cheap Mexican food from Fresh Tortilla (a Chinese-owned Mexican delivery service, according to or gulping pitchers of strawberry margaritas at El Cantinero (without getting carded) was nearly a religion. For me, this day rounds out a 30 day cultural world tour, beginning with Matzoh ball soup and Manishewitz with a layover among Cadbury cream eggs and ending with anything that looks or tastes remotely Mexican.

Since my “Mexican roots” begin and end in my days as an undergrad, I usually spend Cinco de Mayo with friends from that era and, fortunately for me, they all happen to love good food as much as I do.

A few years ago, my longtime friend from both college and childhood, Dave, showed up at my door on May 5 with a bag of churro batter (he knew where I kept my deep fryer) and an unmarked aluminum can that looked something like what you see in the picture below. It took only a few minutes of incessant pestering before Dave revealed the luscious content hidden inside: DULCE DE LECHE.

It turns out, as I’ve come to learn, that dulce de leche is commonly prepared by simply boiling a can of sweetened condensed milk (the kind you buy at Thanksgiving for pie making and find 9 months later in the back of your pantry) for 3-4 hours. The prolonged exposure to high heat caramelizes the sugars in the milk and turns it into a thick brown sauce suitable as a condiment for churros, a topping for ice cream and even a replacement for syrup on pancakes. For those of you who are traditionalists, you can find a step-by-step guide for making dulce de leche the old fashioned way here, here or here. Or, you can just read below for a synopsis of what all these articles say:

An aluminum can of sweetened condensed milk that has been boiled for 3-4 hours.
  1. Poke a few holes in the top of a can of sweetened condensed milk.
  2. Fill a pot with enough water to submerge most of the can, but don’t submerge it completely. (You don’t want water to enter through the holes.)
  3. Bring the pot of water, with the can submerged, to a rolling boil and let cook for 3-4 hours, adding more water whenever there is noticeable reduction in the water level from evaporation.

Simple enough, eh?

It sure is! Except for TWO SMALL PROBLEMS:

  1. 3-4 hours is a long time. Okay, not in the grand scheme of life. But how do you know if you should cook it for 3 hours and 9 minutes, 3 hours and 29 minutes or 3 hours and 59 minutes? The variability of time (and temperature for that matter since boiling water isn’t always the same temperature) creates variable results. And since an aluminum can is opaque, you can’t judge doneness by sight.
  2. If you’re going to go through the trouble of babysitting a pot of boiling water for 3-4 hours, you might as well make a large quantity. But the process of poking holes in the top of the can allows airborne impurities to come in contact with your food and in turn reduces the shelf life of the cans contents. (Think of a can of tuna. You can eat a sealed can that’s been in your pantry for 12 months but not an open can that’s been in your fridge for 12 days.) But not venting the can of milk before you heat it can (theoretically) cause the pressure to reach such heights that it will explode. (Authors note: I’ve made ducle de leche about a dozen times using the can method and I’ve never poked holes in my cans and never had an explosion. I guess I’m a real risk taker!)

So, this is where our problem solving quest begins:

  1. Find a way to make the dulce de leche cooking process consistent time and time again. We want predictable results.
  2. Find a way to keep the stuff shelf stable, as if it were still in a sealed can.
  3. If possible, find the perfect “doneness” and, once achieved, see item 1 so you can make it year after year.

Entrée: The Immersion Circulator

Polyscience Sous Vide Professional
Polyscience Sous Vide Professional set at 180 degrees farenheit

What better way to control time and temperature than cooking our milk sous vide using my new immersion circulator from Polyscience? (If you’re unfamiliar with sous vide cooking, click here, here or here. The basic premise is that by cooking a food at or n

ear the temperature at which you want the final product, you can extend the cooking time decreasing your margin for error and achieve the perfect doneness and uniformity throughout.

The key benefits of cooking my dulce de leche sous vide are significant:

  1. By sealing the milk in a vacuum bag and immersing it in 180-degree water, I can pasteurize the contents and obtain a shelf life similar to that of the original sealed can. Moreover I can actually see the color of the milk as it starts to caramelize, which will help me gauge its doneness.
  2. By cooking the milk at a consistent 180 degrees I can ensure consistent results because (a) the temperature is exactly the same each time and (b) the relatively low temperature will prolong the cook time giving me a larger window of opportunity to stop the cooking process (there will be relatively little difference if I remove the milk after, say, 12 hours versus 12 hours and 30 minutes).

With that, we’ve checked two things off our list—consistency (goal 1) and freshness (goal 2). We’ve still got to find the recipe that makes the best tasting dulce de leche. Because, after all, if the new way doesn’t taste better than the old-fashioned way, it’s got no business being on my dining table.

So how does one achieve dulce de leche perfection? With a controlled experiment and a blind tasting, of course!

The Experiment:

Sous Vide Dulce De Leche
Sous Vide Dulche De Leche: 7 samples of sweetened condensed milk that have been cooked for 2-14 hours at 2 hour intervals (the eighth sample at the back is uncooked).

We cooked 7 samples of sweetened condensed milk at exactly 180 degrees Fahrenheit for varying amounts of time, ranging from 2 to 14 hours, removing a sample at the end of each 2-hour interval. The results are, according to my wife Laura, a study in Benjamin Moore tan paint chips (see the picture to the right).

So right about now I bet you’re wondering if I found the perfect formula and now live in a world of dulce de leche nirvana, right? Well, I’ll have to keep you in suspense for another few days. The old college crew will be coming over on Thursday and we’ll blindly sample all 7 specimens to determine the winner. Stay tuned….

Authors Note: In the many positive comments I received about this article, I did get two important emails from my food science friends on my claim that the milk was pasteurized and sealed in a vacuum bag and thus it would keep as long as the can of sweetened condensed milk. This, I’ve come to learn, is not true. The pasteurization process kills many of the bacteria and living organisms but does not sterilize the milk and therefore bacteria that cause serious ilnesses like botulism can still flourish. Consequently, the dulce de leche should be kept in a fridge and consumed within about two weeks after making it. Alternatively you can consider sterilizing the materials using methods commonly practiced in canning or brewing.