A reader recently called for help with a milk mix-up.

She’d accidentally grabbed a can of evaporated milk from the grocery store shelves instead of the sweetened condensed milk she needed for a recipe. She wondered if there was any way to substitute one for the other.

It’s an easy mistake to make. Both evaporated milk and sweetened condensed milk are heated until about 60 percent of the water evaporates.

It’s the “sweetened” part that’s the problem. Sweetened condensed milk contains about 40 to 45 percent sugar. Evaporated milk is unsweetened, so there is no way to substitute one straight across for the other.

But can you make your own sweetened condensed milk from evaporated milk? After searching through a boggling array of Web sites with advice and admonitions, I decided to turn to the “Food Substitutions Bible,” by David Joachim.

According to Joachim, if you don’t have a can of sweetened condensed milk (14 ounces) you can substitute 1 cup evaporated milk plus 1 1/4 cups sugar, heated until the sugar dissolves.

I would approach this substitution with caution. (In other words: Don’t use it for your holiday fudge recipe if you can help it.)

Even Joachim suggests that something that might be necessary in a pinch isn’t guaranteed to give you the results you’ve come to expect from a recipe: “When it comes to cooking, I truly believe that there ‘ain’t nothing like the real thing.’ ”