Donut dough rising in the oven

How & why a water roux improves your donuts

Great things happen in cooking when you use a technique that you would normally use for one application in a new and inventive way in something totally different. That’s why I was so curious to test out using a roux (which I would normally use for thickening sauces) in a donut recipe. I read it would improve donut consistency, so wanted to try it out to understand what would happen. Would it give me a better donut, or just a different one?

What is a water roux?

Water roux is a type of roux. A roux is a mixture of flour and liquid (e.g. water, milk, stock, but also oil or butter) that has been heated. By heating and stirring the mixture you induce all sorts of transformations in the flour, which we’ll come back to soon. If you heat a roux just slightly it will be perfect for thickening soups and sauces (e.g. for a bechamel sauce in lasagna). Heat your roux further and it will slowly lose its thickening power, but it will become a powerful contributor to flavour.

A water roux is one of the simpler types of roux, consisting only out of water and flour. The ratio of water to flour determines its functionality. For the donuts we’re making here (see full recipe at the bottom of the post) you add about 5-6 times as much water to the the flour (in weight). The water should be at room temperature at this point, it should not be warm. This ensures that you can easily mix the flour and water together (hot water may lead to clumping). You then gently heat up the mixture in a pan on the stove. Gently, because you don’t want it to burn on the bottom. As it heats up you will notice that the mixture starts to thicken up, this is the flour at work. This occurs at approximately 65°C.


Tangzhong is another name for water roux that you might find being used in recipes. It is the same concept, just the Japanese term since it is regularly used in Japanese breads.

Why does a water roux thicken liquids?

Thickening of the water roux upon heating is all caused by changes in the flour itself. Wheat flour consists of starch (a polysaccharide) and gluten (a protein). In water roux the gluten don’t play such an important role, it is the starchwe have to focus our attention towards to.

Starch is a collection of very large complex carbohydrate molecules, one such molecule consists of thousands of glucose molecules bond together. Most of these long molecules organize themselves into starch granules.

When starch is dissolved in cold water it will only absorb a little bit of water, which will make it easy to mix with the water. The starch granules ‘hide’ some of the starch making it easy to mix the two together.

When you heat up the starch it absorbs more water. From around 50-60°C the starch loses its organized structure, some of the granules burst. All these individual molecules will bind water. As a result it thickens the liquid since not all the water flows freely anymore. We call this gelatinization of starch. It also happens when you cook potatoes, make another type of roux, a creamy creme patissiere or boil bagels.

This is why you use water roux in donuts

It took me a little more trouble to find this out since there is no obvious reason for wanting to thicken a bread. But based on what I read I think the following is happening. When baking bread in the oven starch absorbs moisture and breaks down slightly while forming a dough. However, this will not happen to all the starch. A lot of broken down/gelatinized starch is present in a dough though, the better it is in absorbing and holding onto water.

When using water roux the starch has already broken down and gelated slightly. Therefore, relatively more starch has gelatinized. This allows the starch to hold on to more water. More water, means a more moist bread. It should even hold on to the water better, so the donut should become dry less easily, prolonging shelf life.

So, adding this water roux to my donuts, should have made them more moist than without. Furthermore, its shelf life was probably prolonged. Its a shame my donuts were finished so fast, I didn’t have a chance to see how long they would hold… However, it does give me a good reason to try the recipe again!

Water roux donuts

I used a recipe from 350 degree cooking, which I tweaked a little, especially the topping, I like chocolate on my donuts.

Donut with sprinkles and chocolate

Making donuts - discovering water roux!

Yield: 6 donuts
Prep Time: 2 hours
Cook Time: 2 minutes
Total Time: 2 hours 2 minutes


Water roux

  • 20g flour
  • 120g water


  • 160g flour
  • 2 tbsp sugar
  • 1/4 tsp salt
  • 20g butter
  • 60g milk
  • 1/2 egg
  • 1 tsp yeast
  • all the water roux

Chocolate topping

  • Cream and chocolate in a ratio of 1:1.


  1. Make the water roux by mixing cold water and flour in a pan and slowly heating it. You will see it thicken as it goes, keep on stirring. Take it off the heat once it's thickened, do not let it brown.
  2. Once that's finished leave it to the side and make a regular bread dough by mixing the flour with the sugar, salt and yeast.
  3. Add the butter, milk and egg to the flour and start kneading on your stand mixer or by hand. Keep on mixing for a while and then add the water roux. Leave to knead for another 10 minutes or so.
  4. Cover the dough and place in a warm spot to rise, leave for approx. 45 minutes.
  5. Push it down and leave for another 30 minutes before you roll it out into the flat sheet. Cut donuts out of the dough and leave to rise for another 30 minutes (cover the donuts to protect them from drying out).
  6. Fry the donuts in oil of 180C. They will pop up as soon as you put them in and should require only 45s frying per side.
  7. Take them from the oil and soak on a kitchen towel.
  8. While they are cooling down, melt chocolate in the microwave and mix with the cream. It should give a delicious rich ganache. Make as much as you like and smear it over the donuts. If you prefer it a little sweeter, add some glucose syrup, but I like mine slightly bitter.


On Food and Cooking from Harold McGee, AAC net, Bakeinfo New Zealand, Somamiko blogspot, Pastry chef online.

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  • Hi there! Loved your scientific analysis of tang zhong (aka water roux). This is a technique we often use in making Japanese or Asian style “milk breads” to make them soft and fluffy (without going stale too fast).

  • Glad you found my article useful. I love the Tangzhong method. And now I *need* to give it a try with doughnuts, although just like with you, mine would be gone too quickly to see if Tangzhong extends shelf life! lol

  • Hi i just did your recipe using water roux.. Is it normal? Cause my dough is soft and sticky? Thank you

    • Hello, thank you for coming by! The dough is slightly more sticky and wet than a normal bread dough due to the water roux and high moisture content. However, you should be able to roll it out. Here are a few tips that might help: make sure that when you make the roux it has thickened up properly (it shouldn’t flow freely anymore). If it still feels too wet after it has risen, feel free to add some extra flour to knead and form it (it’s a pretty delicate dough, so be generous with flour to prevent it from sticking to the surface). Last but not least, I’ve noticed that flours from different regions require more of less water, if your dough hasn’t come together into a ball before adding the water roux but is still very wet, add some extra flour to compensate. Hope this helps!

    • Hi Tyler,

      Thanks for coming by! The majority of sources I have found state it is Japanese so I based my statement on that. That said, it is also used by the Chinese and I found statements for both, a few examples for Japanese are this one or this one) or this one, for Chinese I found this one.
      As usual with food history, origin stories of food tend to be messy and not super clear, so it might have been either. If you have a reliable source for me to quote on the Chinese origin, I’d be happy to include that as well!

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