raw potatoes

What is Potato Starch and How is it Made?

Have you tried making a recipe that calls for potato starch and wondered what it is and why it’s in your recipe? If so, you’re at the right place. We’re going to dig into the science of potato starch, explaining you just exactly what potato starch is and how it’s made (even how you could make it yourself).

This is another article in our “Understanding Ingredients” series. In this series we dig into the science of ingredients we use to make our food.

What is Potato Starch?

Potatoes are tubers. Every potato is the potential starting point for a brand new potato plant. Plant a potato and you can grow a whole new potato plant. However, to grow into a new plant, a potato needs to bring along a lot of food. A potato stores this food in the form of starch. Since the main role of potatoes is to grow into a plant, a potato contains a lot of starch. Starch is the most abundant component of potatoes, after water (which makes up over 80% of the potato). So what is this starch made of?

Starch Chemistry

Plants (just like humans) use glucose (a sugar) to provide energy to grow and thrive. They make this glucose using photosynthesis. In this process, they use sunlight and carbon dioxide from the air to make glucose.

glucose molecule
A glucose molecule

In order to prepare for times that less glucose is available or, like the case of potatoes, to prepare for future growth, plants need to store this glucose. They by linking a lot of these glucose molecules together, creating a long chain of glucose molecules. These long chains of glucose are starch and are what we would call a polysaccharide! (Note, we humans use a similar concept for storing excess glucose, however, instead of making starch, we make glycogen.)

Starch is an energy reserve for the potato, consisting of long chains of glucose molecules.

The glucose molecules can link to each other in roughly two ways. One by forming a long, mostly linear, chain of glucose molecules. Each glucose molecule (except for those at the end) is linked to two others. The molecule formed this way is called amylose. Alternatively, the glucose molecules can connect in a more branch-like structure. In this case, some glucose molecules are connected to 3 other glucose molecules, creating offshoots of the linear chain. This branched structure is called amylopectin.

Starch contains a mixture of both amylose and amylopectin, just how much of each depends on various factors. For instance, starch from potatoes is different from that of rice. But also, younger potatoes can have a different ratio than older ones and different potato varieties will have different ratios. In potatoes about 20-35% of the starch tends to be amylose, the remainder is amylopectin.

Starch granules

Potato starch is present throughout most of the potato in the form of granules. Each granule will consist of a large number of starch molecules, including both amylose and amylopectin. The granules are very tightly packed (hence their storage function), so tightly packed that the density of these granules is higher than that of water (1.5 g/ml). It is why raw, uncooked starch sinks in water.

The starch molecules are packed in such a way that they create a semicrystalline structure. This very well-organized structure makes starch insoluble in water at room temperature (once you start heating the starch granules that all changes, as we discussed for cooking potatoes and starch thickeners).

Granule size & shape

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Granules in potato can vary in size from as little as 1 micron (= 1/1000th of a millimeter) up to 100 times (roughly 110 micron) that size. The smaller granules are spherical or oval in shape whereas larger ones are cuboid or even irregular in shape.

We won’t go into too much detail here but the shape and size of granules play an important role in how a starch behaves. Potato starch granules tend to be on the large side. Also, if you’d look at the granules under a microscope you’d notice that their shape is quite different from that of wheat or corn for instance. This all impacts the behavior of the different starches and makes them all slightly different.

Non-starch ingredients (e.g. phosphates)

Even though starch granules are mostly made up of starch, a few other molecules may have come in as well. For instance, some protein or fat molecules might be present. In the case of potato starch, you will likely also find some phosphates. Even though they make up a small portion of the granules, they do impact their behavior. The phosphates contribute to the high water-binding capacity, viscosity, transparency, and freeze-thaw stability of potato starch.

How Potato Starch is Made

To make potato starch manufacturers start by choosing suitable potatoes. To make potato starch manufacturers prefer potatoes with a high starch content, this way you get most potato starch out of your incoming potatoes.

Once the potatoes have been washed and cleaned it’s time to separate the starch from the rest of the potato. Keep in mind that potatoes are over 80% in water content. Of the remainder, more than half of the potato is made of starch, but there’s also a little bit of protein as well as some fibers.

Shred the potatoes

To get this starch out of potatoes, they are first shredded up finely in small pieces. This process breaks up all the cells of the potato. Starch sits within those cells and is released into the water. By rinsing the mashed up raw potatoes as much starch as possible is extracted from the potatoes.

Let the starch sediment out

The starch that leaves the cells and enters the water isn’t made up of individual molecules. Instead, starch is present in the form of larger granules, thus visible particles. These granules don’t dissolve in water. Instead, if left standing long enough they will sink down to the bottom of the water. In factories the water + starch is gently led through long ‘channels’, this gives the starch the chance to sink to the bottom and sediment out (it’s the same sedimentation process that would happen with your chocolate milk where cocoa particles sink to the bottom).

At this point, the starch mixture still contains a lot of water so it will need to be dried even further to form a dry powder. A challenge here is that these starch granules are quite large, making them mostly unsuitable for a fast technique such as spray drying. Also, you shouldn’t heat the starch too much. Once starch has been heated, it permanently changes its structure. As a result, it won’t have the same thickening effect anymore. In other words, its functionality has changed.

Modified potato starch

Manufacturers have found ways to modify starches, including those from potatoes, to make them more suitable for their applications. Starches that have been modified are modified starches (and often labelled as such). There is a wide range of possible modifications. Manufacturers might use enzymes, acid hydrolysis, or one of several other possible types to tune the starch to their application.

Can you make potato starch at home?

Yes, you can make potato starch at home and you would use a very similar process as they’d use in a factory! You also start by crushing (or grating) the potatoes and rinsing them several times to break down the potato cells. Next, you will have to wait for the starch to settle down and rinse it a few times. In the references below we’ve referred to a good guide from Wikihow.

Keep in mind that the quality of you homemade potato starch will be more variable than factory made one! How your starch will behave depends on the type of potatoes you’ve used and just how much and what type of potato granules they have. Of course, if you’re application is quite generic, that doesn’t matter too much. But if you’ve got a specific cake recipe you’re making, you might benefit from the consistency of factory made potato starch.

Using Potato Starch: What happens when you heat it

Now that you’ve got your potato starch, you might be wondering what to do with it! The most important first step: heating the potato starch. Raw, uncooked potato starch consists of mostly resistant starch. These are those semicrystalline starch granules. This type of starch cannot be digested by the human body. You need to cook/heat it to make it digestible.

Granules swell and break

We’ve discussed what happens when you cook/heat potato starch in more detail when discussing what happens when you cook a potato. Since the majority of the dry matter of a potato is made of starch its transformation is the most important one.

First of all, you would mostly use potato starch in the presence of water. As long as the starch is cold is won’t dissolve in the water, but it will absorb a little. Once you start heating the starch it will absorb more and more water, swelling up considerably. At some point, when it’s hot enough, it will have absorbed so much water that it breaks and releases all those individual starch molecules.

Thickening

These starch molecules are very long and love water (they’re hydrophilic). As such, they will bind a lot of water and thicken liquids. It’s why you often use starch as a thickener. When you use potato starch it will almost always be used at least in some way for its thickening properties.

Retrogradation

This process of swelling and breaking is irreversible. Cooling down your potato starch sauce or liquid will not bring it back to its original consistency. However, it won’t remain freshly cooked either. Instead, once the cooked potato starch cools down the starch will undergo a process called retrogradation. During this process, the starch recrystallizes to some extent. Potato starch specifically is known to retrograde considerably compared to other starches.

The retrogradation process of starch is also what makes fresh bread turn stale!

What can Potato Starch be Used for?

Just like most other starches, potato starch is often used as a thickener. You might find it being used in soups or sauces. Also, you can find it being used in cookies or cakes to replace (part of) the wheat flour (we tested that more extensively here). This tends to give very brittle (sandy) cookies and lighter cakes compared to using just regular wheat flour (thanks to the lower protein content).

Did you know though, that some of the major users of potato starch aren’t food manufacturers? On the contrary, potato starch is used a lot by both the paper and glue (adhesives) industry!

References

James BeMiller & Roy Whistler (editors), Chapter: Potato Starch: Production, Modifications and Uses, Starch: Chemistry & Technology, 3rd edition, Elsevier, 2009, link

W Bergthaller, Chapter 8 Developments in potato starches, Starch in Food: Structure, Function and Applications, CRC Press, 2004, link

Sreeshna Jagadeesan, Indira Govindaraju, Nirmal Mazumder, An Insight into the Ultrastructural and Physiochemical Characterization of Potato Starch: a Review, American Journal of Potato Research (2020) 97:464–476, link

H. Panda, The Complete Technology Book on Starch and Its Derivatives, 2-Jan, 2004, chapter 7, p. 137-145, link

Jaspreet Singh, Rosana Colussi, Owen J. McCarthy, Lovedeep Kaur, Chapter 8 – Potato Starch and Its Modification, Advances in Potato Chemistry and Technology (Second Edition), Academic Press, 2016, Pages 195-247, ISBN 9780128000021, https://doi.org/10.1016/B978-0-12-800002-1.00008-X. Viewed at

USDA, Food Data Central, Potatoes (FDC ID 170032), link

Wikihow, How to Make potato starch, 30 Nov 2020, link ; extensive guide to making your own potato starch at home

Kequan Zhou, Margaret Slavin, Herman Lutterodt, Monica Whent, N.A. Michael Eskin, Liangli Yu,
Chapter 1 – Cereals and Legumes, Biochemistry of Foods (Third Edition), Academic Press, 2013, Pages 3-48, ISBN 9780122423529, https://doi.org/10.1016/B978-0-08-091809-9.00001-7. viewed at

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