I was making a filling for a refrigerated pie with 1 1/2 cups sugar, 6 tablespoons cornstarch, 1 teaspoon salt, and 1 1/4 cups water blended and brought to a boil. The instructions said to boil for two minuntes until thick and bubbly. When it was thick and bubbly, I add 2 teaspoons butter, 2 teaspoons grated lemon peel, and 2/3 cup lemon juice. It said to bring it to room temperature to thicken, then I would be able to put it on top of a cream cheese filling and chill overnight. Okay. Now for the problem: The filling thinned out as soon as I took it off the heat and added the butter. It never thickened again. I even put it in the fridge after a while. It tasted great, but was really runny. Can you figure out what I did wrong? Thanks. --iVillager suzanne_cooks
Cooking with cornstarch is tricky. I have ended up with pie custard that wouldn't set myself. The timing of adding in the lemon juice is the key. You need to bring the mixture to thick and bubbly and then remove it from the heat. Let it sit a few minutes only before adding in the last ingredients. During cooking, if you add in lemon juice, it causes the mixture to thin permanently, as you have already found out. And if you boil a cornstarch thickened filling for more than three minutes, it will thin out.
Here's another technique to try: First combine the cornstarch and sugar together. Then, whisk in the water to dissolve the cornstarch. Bring the mixture to simmer over medium heat. The mixture will be very thick. Reduce the heat to low, then simmer and stir for 30 seconds. Remove from the heat and stir in the butter, lemon juice, etc. Strain, if necessary.
Sarah Phillips is the author of Healthy Oven Baking Book.