Shirley is one instructor, syndicated columnist and also author of 2 award to win cookbooks.

You are watching: Why are my scalloped potatoes still hard

Through the years, I have actually had many calls around lumpy gravy and an amazing variety of “Why wouldn’t my scalloped potatoes cook? The potatoes space rock-hard after two hours.” So, just how do potato cook? as the potatoes heat, the strength granules in them take it in fluid to swell and also soften to “cook.” with both lumps and also non-cooking potatoes, us are handling starch.

How starch Works

Starch granules contain 2 kinds of strength (amylose and also amylopectin) packed together layer on top of layer prefer an onion. When you stir starch granules into cold water, a small water begins to seep in. Together you warm the starch and water, more and more water look in. Somewhere in between 66°C/150°F and 100°C/212°F (depending top top the form of starch), the granule may organize hundreds of times its load in liquid. As soon as the granule have the right to swell no more, it pops. Strength rushes out right into the liquid. This is once your sauce or gravy thickens.


Both the strength particles and also the big, empty, jellyfish-like granules contribute to the thickening. Friend don’t desire to stir also vigorously, or you might smash these large empty granules and also the sauce or gravy will certainly thin.


If friend spoon dry starch (flour or cornstarch) into a hot liquid, the starch on the outside of every lump will swell instantly to kind a gelatin coating, keeping the bump dry for you to bite into. To protect against lumps, the three standard methods of prepare starch-bound sauces spread the starch out grain by grain. In a roux, the starch is blended with fat. In a slurry, the strength is stirred right into cold water to disperse it. In a beurre manié, equal portions of butter and flour are operated together. Then, once this mixture is added to a hot liquid, the butter melts and also disperses the flour grain by grain—no lumps.

Starch will Not Swell–Rock-Hard Scalloped Potatoes

Potatoes or rice deserve to remain rock-hard after lengthy cooking. Starch will not swollen if it is acidic. If you have a the majority of sour cream in your scalloped potatoes or include something acidic, your potatoes might not soften. You can cook the potatoes with heavy cream or milk and then, after castle soften, row in sour cream. If you have actually a many of really acidic tomato in a paella, the rice might never soften.

Pat and Betty, chefs because that Reynold’s Wrap, were occurring whole enjoy the meal (meat, vegetable, and also starch) recipes the were wrapped in separation, personal, instance packets for each member that the family and would chef in 20 to 25 minutes. To simplify the recipes, they used salad dressings come season rather of using salt, pepper, herbs, and also oil. They had a cooking recipes in which the potatoes would certainly not cook. They thought the potato pieces were too big, yet when they gained them down to the size of rice and they were still uncooked, they dubbed me.

The trouble was the really acidic vinaigrette salad dressing that they to be using. When they switched to a milder dressing the potato cooked perfectly.

This is additionally the factor that lemon pie recipes the are an extremely lemony will instruct you to warm the starch, water, and also sugar until the starch thickens and then add the lemon juice and egg yolks.

Starch in other Thickening

You may have seen a rice pudding v the rice in a dense layer on the bottom and also the custard ~ above top. This was probably made with refrigerated leftover rice. When cooked grain starches are chilled, the starch crystallizes into a firm network. When reheated, the crystals will melt and the starch will soften. But, together a strength will never ever exude starch to thicken. So, in a rice pudding made through this rice, the rice can not contribute any type of thickening.

The pudding is not thick enough to organize up the rice therefore it sink to the bottom. A good restaurant must use your leftover rice. They can sprinkle a few tablespoons that cornstarch over their rice, then blend it in v the other ingredients for a regular rice pudding. If you usage leftover rice because that my gold Brown Puffed Cheesy Rice Spoon Bread (see recipe), the tablespoon the cornstarch is vital.

Starch prevents Curdling

To the cook, starch deserve to be a an excellent hero by staying clear of curdling. Protein (egg or dairy product proteins) have the right to join as soon as heated, exposed to mountain or also air, and can become a curdled mess.

For example, if you to be converting a high-fat cooking recipes with heavy cream right into a low-fat recipe with skim milk or low-fat yogurt, girlfriend can gain curds. The proteins in the cream unwound through heat yet they were coated with fat therefore they walk not join to type curds. Yet low-fat milk or yogurt has loads that proteins and also no fat to keep them apart therefore you obtain a mass of curds.

Most home-use starches favor cornstarch, flour, tapioca, potato starch, or arrowroot can prevent this curdling. The exact mechanism is no known. It might simply be the the starch swells enough to it is in “in the way” and prevents protein from joining. A girlfriend of mine who taught great in low-fat food preparation would row a tablespoon of cornstarch right into a quart the low-fat yogurt and then usage that to make creamy sauces and also quiche.

Starch avoids Shrinkage of Meringues

Egg white proteins in meringues shrink once you chef a meringue. Not just does the meringue pull far from the leaf of the pie, it becomes complicated to cut. Starch can prevent this. Row 2 teaspoons cornstarch right into 1/3 cup cool water and heat until it thickens come a paste. After adding the sugar, near the finish of beating the meringue, add this starch paste a teaspoon in ~ a time. It will certainly interfere v the egg white proteins’ chop coagulation and will make a meringue the shrinks less and cuts without pulling or tearing.

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Custard Thinning

If friend stir a custard after ~ it has actually cooled and set–say to stir in grand Marnier–some of the starch bonds will certainly be broken and the custard will thin.


Shirley Corriher

Shirley O. Corriher has taught indigenous Vancouver to Sicily, has composed an internationally syndicated column, and is an award-winning author. Her book CookWise was the James Beard award winner for ideal Reference and Technique publication of 1997 and has marketed over 500,000 copies. Real straightforward magazine lists CookWise as One of the 50 good Books the Will readjust Your Life. BakeWise also winner a James moustache Award and also was named by food preparation Light newspaper as one of the 100 Best Cookbooks that the previous 25 Years.