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This is a guest post by Karen Rutherford founder and editor-in-chief at the Cakedecorist.
I was making cheesecake the other day and thought it could do with a strawberry sauce on top. So, I set out to boil down my fresh strawberries from the farmer’s market with some sugar, to create a thick and luscious sauce.
As it turns out, I put too many strawberries into it and it took SO LONG to cook down that I almost gave up halfway. Luckily, I still had some cornstarch in my pantry. So I added a couple of tablespoons and within a few minutes my sauce was done! It turned out so good that it inspired me to explain how to use thickening agents for baking, as they can be handy in many situations.
What is a thickening agent?
Before zooming in on starches specifically, let’s have a look at what thickening agents even are. A thickening agent is a substance that can be added to food to make it creamier and, of course, thicker. They can be used anywhere, really, but can be especially helpful for bakers. You can use them to thicken a sauce, to fix some loose batter or filling, to create gel-like textures, and so forth.
Understanding how to cook with these ingredients will help you achieve the consistency you need for every preparation.
A lot of thickener agents are made of polysaccharides, which are very large carbohydrate molecules. These long carbohydrates interact with and absorb water, which causes them to thicken liquids and achieve gel-like consistencies.
There are a lot of different starches that all work a little differently depending on what plant they come from. Wheat flour, for instance, contains a high amount of starch. This starch behaves differently than potato starch, cornstarch, arrowroot, or tapioca starch. Starches are great to use in preparations that will be baked or in sauces as they need to be cooked off to get rid of their raw taste. More on starches further down!
Pectin is the magic behind jam and jelly and it’s another polysaccharide thickener. It is a part of a lot of fruits and transforms cooked fruit into a gel-like consistency when they are cooled down. Because of its firmness, adding cooked down fruit purees to other mixtures will make them thicker. Different types of fruit contain varying amounts of pectin. As a result, some fruit purees are considerably thicker than others.
Xanthan gum is a product created from the fermentation of sugar, carried out by a bacteria called Xanthomonas campestris. It is a common food thickening agent and a stabilizer, for instance in ice cream.
It is commonly used in gluten-free products to resemble the properties of flexibility and texture that gluten gives to food (like baked goods). To use xanthan gum in baking, mix with the dry ingredients of the recipe. If you are baking a gluten-free recipe, it is recommended to use more than one type of gluten-free flour (rice flour, tapioca, or chickpea flour).
Agar-agar comes from red algae and it is high in protein and fiber. It is used as an alternative to gelatin to thicken, stabilize, and give texture to baked goods, sauces, glazes, coatings, dairy products, and in small amounts to make jams.
To use agar-agar for water-based icings, dissolve it in a mix of sugar and hot water, then incorporate the rest of the ingredients. If your recipe is fat-based, blend the agar-agar with the dry ingredients, add it to the fat and then heat the whole mix.
Proteins can also be used as thickening agents. For example, egg whites or gelatin. The end result is more of a gel-like texture and so they are not suitable for the same purposes as starches are.
Egg whites thicken a mixture irreversibly once they’re cooked. The proteins denature and set the structure, which is what makes eggs so important for cakes. Gelatin, on the other hand, forms a reversible structure. You can re-heat a mousse thickened with gelatin and it will soften again. Cooling it down will then re-set the gelatin. By incorporating some gelatin, the cake will hold its shape under much higher temperatures.
For the rest of the articles I’ll focus on using starches as thickening agents since they are especially helpful when baking!
How Do Starches Work?
Any thickening agent will absorb or hold onto water. This is what causes them to thicken a liquid. Starches do so as well, but only when they’re heated.
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Starches are composed of polysaccharides that, depending on their origin, have a different ratio of the two main components: amylose and amylopectin. They are distributed in granules that, when combined with water and heat, go through a gelatinization process. During gelatinization the granules swell. This allows water to attach irreversibly to the granule. This makes it larger and combines the starches properties with the water itself, causing it to gel. It increases viscosity and give stability to the ingredient mix. You can visibly see your sauce thickening when doing so!
The gel that results will be more opaque and firm if the starch had a higher amount of amylose. If it has a higher amount of amylopectin, then it will form a paste. This paste will be more translucent and remain fluid when cooled.
Impact of amylose:amylopectin ratio
A high-amylose corn starch will give you a more opaque, firm, and stronger gel. Keep in mind that there are three different types of corn starch (regular, waxy, and high-amylose starch with 26, 1, and up to 80% amylose respectively). Although in the supermarket you will only find one.
Tapioca and potato starch will form a paste texture, their amylose: amylopectin ratio is different from corn starch, they have between 17 to 22% of amylose.
In general, the amount of amylose in the starch gives strength to the gel and amylopectin gives high viscosity.
Gelification is not the last step that thickening agents can achieve. Each type of starch has its own gelatinization temperature according to its amylose: amylopectin ratio. If the starch is heated up further, over the gelatinization temperature, and stirred while cooking, then you can reach pasting. This means maximum thickness, it is when the slurry doesn’t have a starchy taste, the texture is smooth and can cover the back of the spoon.
Differences between starches
The gels that each type of thickening agent can deliver will vary in transparency and stickiness. Each of them will also need to be added in different amounts to create the same results. This is also the reason why they are not so easy to interchange or replace.
For example to substitute starches: 2 tablespoons wheat flour = 1 tablespoon cornstarch = 1 tablespoon tapioca = 4 1/2 teaspoons arrowroot = 1 1/2 tsp. potato starch.
When to use starches
Starches are usually used for sauces, gravies, soups, or pie fillings; for example, a roux, which is a French base for many sauces, is made out of wheat flour. But they can also be used for baking with excellent results.
When using starches, dissolve it first in a bit of cold water and create a slurry. Then mix it into your sauce that needs thickening. Only when you start heating does it thickening power activate. If you would not create this slurry at first, you would end up with a lot of clumps in your sauce! If that does happen, remember that you can often smooth it out with an immersion blender.
My best piece of advice for these is to start small. Add a little bit at a time of the chosen ingredient and stir until you reach the consistency and look that you are going for and stop there. Although thinning down a preparation that is too thick is easy enough, it does entail adding more and more ingredients, changing the original recipe. So take it slow!
Pros of using starches
Starches do not add flavor to the mix you want to thicken, if anything, they can bring down the flavor. They do not add any fat and tend to be inexpensive. They can add an attractive sheen to your sauces.
Cons of using starches
They react differently to temperature and not all of them tolerate extreme heat such as arrowroot or cornstarch, but they still need to be cooked. If not, they will leave a residue of raw flavor. It is why they should not be reheated.
To prevent the starches from breaking down, heat at very low flame, check the gelatinization temperature of the starch you are using and take care that it does not rise above 2 or 3 degrees, keep stirring the mixture at all moments.
If overcooked, starches can actually break down. If this happens, then instead of a thicker mix you will end up with a slurry.
Available Starch Types
Wheat flour, cornstarch, arrowroot, and tapioca are the most widely starches for thickening. But others like potato starch or other types of gluten-free flours are also quite common.
Remember, though, that wheat flour has half the thickening power of cornstarch. This is because it is not a pure starch. It has other components like proteins that interfere with its thickening properties.
How and When to use Cornstarch
Cornstarch is a pure starch that comes from corn. It does not break down easily so there is a very low risk of overcooking it or over stirring it. Because of its high amylopectin content, cornstarch will give the end result a great sheen.
These two properties (resistant to heat and shiny finish) make it perfect for a variety of preparations such as fillings that will be cooked and then baked again in the oven or delicate sauces that need to be translucent and glossy. For example, banana cream pie filling, berry pie, and even stove-top puddings.
Its downfall is its tendency to clump. This happens when you sprinkle it on top of hot substances directly. To achieve even dispersion, I recommend you use two different methods.
If you are making a filling, mix the cornstarch with the sugar. This will get rid of any possible clumps before you mix it with your other ingredients. If you are making a sauce, then mix a tablespoon or two of the cooled down liquid that the recipe requires with the cornstarch before adding it into the rest of the preparation.
Always remember to simmer a cornstarch thickened sauce for 1 to 2 minutes to get rid of any raw starchy flavor.
How and When to use Arrowroot
Arrowroot is a tropical plant and we can also derive a pure starch from it. It comes in the form of small granules or powder and you can find it at health-food stores or online.
It resists heat very well like cornstarch and flour. Like tapioca, it delivers a very clear end gel. It also makes everything smooth and you can use it as a cornstarch substitute.
I recommend it for open lattice fruit pies and sauces. Its only drawback is its price. I do think it is worth it if you can get it and make gluten-free desserts, though.
To dissolve the arrowroot powder, mix 1 tablespoon of the powder into 2 tablespoons of cold water, then add it to the hot sauce at the end of cooking. In this ratio, you will obtain a gravy consistency.
Its downfall is its incompatibility with non-frozen dairy products or cream-based sauces.
How and When to use Tapioca
Tapioca is also a pure starch. In this case, it comes from the cassava plant. You can find it in many different presentations. The most widely available is pearl tapioca, usually called instant tapioca. This quick-cooking version is perfectly suitable to use as a thickener. You can also find it as a powder, although it is rarer and maybe more expensive.
Tapioca gels are very translucent. I would say they are crystal-clear even. They also have more of a jelly-like consistency.
As a drawback, tapioca pearls usually do not fully dissolve into fillings. This means that they will be present as clear beads, adding a texture that may not be pleasant to everyone. If you find tapioca starch in powder you can use it instead of the pearls and avoid this problem.
I especially recommend it for fruit pies that have a lot of juice. The beads hold water and make the filling sturdier. It is also great for pies that will be frozen, as they prevent the pie from weeping when reheated.
Make sure, though, that they are not open lattice pies. Exposing them directly to hot air will prevent them from dissolving completely. Also, avoid using them in preparations that require too much stirring or a lot of boiling time like stovetop custards.
To use the beads for a fruit pie filling, I recommend that before you bake them, you let the beads sit with fruit for 5 to 10 minutes. The granules will begin to dissolve into the fruit before even being baked.
After reading about different thickening agents, what do you think about my solution for thickening my strawberry sauce with cornstarch? Would you have done anything differently? Tell me below!
Karen Rutherford is founder and editor in chief at Cakedecorist. You will often find her in the kitchen creating edible works of art or trying out some new recipes. As a pâtissière and baking enthusiast, Karen has decided to share her abundant knowledge with the internet audience and provide only the best tips and recipes for baking and decorating your favorite sweets.
Nicole Rees, Thickeners, Fine Cooking Issue 81, link