“Why does pasta water turn white,” a Redditor recently asked on a subreddit I follow, “and why do some chefs use it after they cook their pasta?”
This is a question so good, I couldn’t resist but write an entire article about it. Keep on reading if you, like me, have ever asked yourself this as you cooked pasta at home.
Boiling pasta releases some of its starches into the cooking water. Starch is dissolvable in water, and breaks down in the presence of water and heat. As it does, it thickens the pasta water, making it cloudy and murky.
If you pour less water or add more pasta noodles to your pot, the concentration of starches in the water will be higher and the water will turn thicker and cloudier.
Don’t throw the cooking water away when you make pasta. Instead, add ½ to 1 soup ladle of it to your sauce as it cooks. The salty and starchy water will help to season and thicken the pasta sauce.
Some cooks (me included) intentionally boil their pasta in less water, so that the cooking water comes out murky. They then use the salty and creamy cooking water as an ingredient in their pasta sauce.
This technique works well on egg, cream, and tomato-based sauces. You can also use it as a “cooking hack” to improve the taste of store-bought pasta sauce.
As a rule of thumb, boil 1 pound pasta noodles with 1 tablespoon of salt in 4 quarts (16 U.S. cups) water.
Why Does the Cooking Water Turn White When You Boil Pasta?
I always wondered why the water in my pot turns white when I’m boiling pasta. And it’s not just me—I’ve heard people ask this question many times before.
Why does it do that?
The answer, it turns out, is in the flour used to make the pasta.
Pasta noodles, as most of you already know, are made by mixing flour and water into a dough.
The dough is rolled out into lasagna sheets or pushed through molds, called “pasta dies,” that turn it into the various shapes and noodles sold at grocery stores.
The freshly-made pasta is then dried, packaged, and distributed, only to end up on the shelves at supermarkets, Italian delis, and mom and pop shops—at least until you buy it, cook it, and serve it for dinner.
Flour is a fine powder traditionally made from wheat. Most baked goods like breads and pastries are made from wheat flour because wheat flour has one important trait: when you mix it with water, it develops a complex protein called gluten.
The gluten is what makes the dough elastic, which allows its bakers to work, knead, and shape it into the bread and pastry we eat, and fresh or dried pasta noodles we cook.
Pasta noodles are made from a specific type of flour called semolina flour.
Semolina flour is a protein-rich flour. When you mix it with water, it develops more gluten than other flour types, which makes it extra elastic and workable.
Elastic and workable dough is exactly what pasta makers are looking for when they make noodles, because it can be shaped into more than 350 pasta varieties like spaghetti, macaroni, penne, lasagne sheets, tagliatelle, and others.
To be elastic and workable, semolina flour is made from a specific type of wheat called durum wheat. Durum wheat is what is known as a hard wheat. Its germs are tougher than those of most other wheat varieties that farmers grow on crops.
Because durum wheat is harder than most wheat varieties, more thorough grinding of the germs is needed to produce semolina flour. This damages some of its starch contents, which in effect reduces its ability to ferment and rise.
This is why durum wheat is used for making pasta noodles and not for making bread, where the ability of the dough to ferment and rise is essential to making a good product.
Durum wheat has a 70-75% starch content. According to the USDA, 100 grams of durum wheat contains 73 grams carbohydrates (the carbohydrate content includes starches, sugars, and fibers). These starches are both on the surface and on the inside of your pasta noodles.
When the noodles come into direct contact with the boiling water, some of the starches on their surface will dissolve. As the starches dissolve and get heated to 212°F (100°C), the boiling point of water, they gelatinize.
Starch gelatinization is when starch granules swell in hot water (thickening and clouding the water as a result).
Starch gelatinization, as Wikipedians explain, is a process of breaking down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water.
This dissolves the starch granules in the water.
Why Your Pasta Water Is Yellow
If you cook pasta often, you’ve probably noticed that, sometimes, the water in your pot turns yellow. Why is that?
When your pasta water turned yellow(-ish), that’s probably because you cooked fresh pasta or dried egg pasta.
Dried pasta is made from a mixture of flour and water. Fresh pasta and dried egg pasta, on the other hand, contains eggs. When you cook pasta that contains eggs, the egg yolk can color the cooking water with a yellowish color.
Should I Throw the Pasta Water Away?
Don’t hurry to throw the pasta water away as soon as your pasta is cooked. Instead, scoop out a soup ladle and add it to your pasta sauce as you’re simmering it. The salty and starchy water will not only add a wheaty aroma to it, but the starches will also help you to thicken the sauce.
This technique, by the way, works especially well for improving store-bought pasta sauce.
Now you know why the cooking water turns white and thick when you boil pasta in a pot. You also know why this salty and starchy water is perfect for seasoning and thickening your pasta sauce.
The next time you make pasta, don’t drain the cooking water into the sink. Save some of it (I usually pour some in a cup) and use it to season and thicken the pasta sauce.
If you’re pan-frying Guanciale, Pancetta, or bacon for your pasta, you can also pour some of the water in the pan to deglaze it.