Thickening soup with cornstarch is a very common chinese cooking technique.
The representative soups using this technique is the hot and sour soup 酸辣汤 (suan la tang) and westlake beef soup 西湖牛肉羹 (xi hu niu rou geng).
Ingredients are usually diced or shredded quite finely and parboiled. Look at the hot and sour soup, all the ingredients are sliced and julienned. Each spoonful contains so many different tastes and textures.
Soups should be lightly seasoned before thickening because it will be more difficult to season well after thickening.
How to prepare cornstarch solution
Cornstarch powder must not be added directly to the soups. The powder is very fine and tend to clump together. They will turn into a gooey blob when mixed with hot water.
To prevent lumps, always mix the cornstarch in some cold or room temperature water first. Place a few teaspoons of cornstarch powder into a small bowl. Add the same amount of water and mix very well. Cornstarch do not dissolve. What you will get is a milky mixture.
When making cornstarch solution, add water to the cornstarch instead of cornstarch to water. Cornstarch is very light and will float on the water making it difficult to mix.
The normal ratio of water to cornstarch is 1 : 1.5 but I prefer to make thicker cornstarch mixture because it means I need to add less to a pot of soup to thicken things up quickly.
How to thicken soup with the cornstarch mixture
Cornstarch will settle if the mixture is left to stand. Always give the mixture a good stir before added to the soup.
Pour the cornstarch mixture into the soup slowly, stirring to check the consistency. You want to achieve a nice smooth slightly thickened texture, not a sticky gruel or a starchy paste.
Stop adding the cornstarch mixture when the texture is achieved, add more if your preferred consistency is not met.
Be patient, do not pour everything in at one go. If you are new at this, for a start, add the cornstarch mixture one spoonful at a time. After adding, stir the soup well. Check the consistency, then add another spoonful.
Art Paste & Clothes Starch?
Do you know that cornstarch can be used to make art paste? Cook a pot of cornstarch with water until it turns into a stiff starchy paste. Edible glue! Child-friendly too.
I once made a paper mache pig using a balloon, card paper, colour paper and cornstarch glue.
Grandma used to soak my uncle's army uniform in a thin cornstarch solution so that it would iron out straight and stiff. I still remember the way my uncle looks when he tried the uniform on for the first time. Too bad, no pictures.
Where to buy cornstarch?
I get the "where can I buy this?" question quite often and although I think cornstarch shouldn't be difficult to find in the supermarket, I thought I will just mention that Amazon has it: ARGO Cornstarch - 35oz. There are of course other brands. Pick the one you trust.
Some thickened soup recipes
Try some of these chinese thickened soups.
Alternative soup thickening agents
Some visitors have asked me whether they can use other types of starchy powders to thicken soups. The answer is yes. Some other possible thickening agents include arrowroot powder, kudzu powder and potato starch. What are the differences?
- Soups thickened with arrowroot powder tends to keep its texture when frozen or cooked for a longer period of time. Arrowroot powder has a more neutral flavour and can tolerate more acidic ingredients. It is more expensive than cornstarch. It is also not as easy to find in the stores. Bob's Red Mill Arrowroot Starch Flour, 20-Ounce Packages (Pack of 4) at Amazon has received good reviews. Yeah, it is also gluten-free.
- Kudzu powder has some medicinal properties. It is therefore more expensive and harder to locate. In chinese traditional medicine, it has been used to control alcohol intake. Recent scientific studies have confirmed this. So I guess it might be good for people recovering from alcoholism? It is commonly sold as capsules or tablets in health shops but the chinese still like to use it naturally. Eden Foods sells it as Eden Foods Kuzu Root Starch -- 3.5 oz.
- Potato starch is gluten-free which is good news for celiacs who wants to try soups like westlake beef soup and hot and sour soups. It is more delicate than cornstarch and will not stand prolong cooking. Add near end of cooking. Potato starch is widely available. Here one from Amazon that is selling quite well: Bob's Red Mill, Potato Starch Unmodified, Gluten Free, 24 oz (1 lb 8 oz) 680 g
Prepare the thickening mixture in the same way as cornstarch. Mix it first with cold or room temperature water before adding to your dish.
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