Does Cornstarch Go Bad?


Cornstarch is one of those ingredients that we always make sure we have on hand. It is so useful in a variety of recipes. If you are anything like us, we reckon you’ll have a bag or box of cornstarch sitting in your cupboard right now? How long has it sat there, and is it still good? In fact, does cornstarch go bad at all? If you are asking any of the following questions, you are about to find the answer. Read on to find out more.


Does Cornstarch Go Bad?

As with most types of flour, cornstarch does not go bad as long as it is stored correctly. In fact, it has an almost indefinite shelf life, provided it is kept away from a couple of harmful elements.

Those being: –

  • Moisture. If you allow moisture into your cornstarch, then bacteria can begin to feed on the sugars held within. As a result, this will turn your cornstarch bad.
  • Bugs. There are a few creatures that love nothing more than to feast on any flour. Weevils, in particular, love a cereal-based treat. However, this shouldn’t be a problem if they have kept away, and your cornstarch will stay good almost indefinitely.

Want to know everything you can about cornstarch? Keep reading.

What is Cornstarch?

While you might not realize it, cornstarch is actually just another type of flour. Unlike other types of flour, such as white or wholemeal flour, cornstarch isn’t made from the entire grain. Instead, it is formed from the very center of a grain of maize (otherwise known as ‘corn’). 

It is milled (a fancy name for ground) until it is really fine before being packaged as an ingredient. 

Depending on where you are in the world, you might also hear cornstarch referred to as ‘corn flour’.

What is Cornstarch Used For? 

You’ll see cornstarch features in lots of different recipes.

It is most commonly used in baking, and you’ll also see it used as a thickening agent in many dishes with a sauce. 

If you have ever used gravy powder or soup mix, you might be surprised to learn that this normally features cornstarch. This is what makes your gravy and sauce thicken up when you add to it hot water or sauce.

Cornstarch is very glutenous. When water has been added, these strands of gluten are hydrated and stretch. On a molecular level, they form a sort of elastic lattice that makes your sauce much thicker.

Cornstarch is also a key ingredient in custard powder too.

If you mix too much cornstarch with moisture, interesting things happen, and you end up with something called a non-Newtonian fluid. This essentially turns to a solid when struck or compressed before turning back to liquid. 

How to Store Cornstarch

The main enemy when thinking about how to keep your cornstarch good is moisture. If you can keep it free of moisture, you can prolong the life of cornstarch significantly.

The best way to store cornstarch is in an airtight container. Keep it in a cool, dry place, such as a pantry or store cupboard. Be sure not to store it along with any strongly flavored ingredients such as onions or garlic, or you may find that it becomes tainted with these flavors over time. 

Aside from bacteria, other bugs love cornstarch. Again, keeping your cornstarch safely stored in an airtight container prevents the bugs from getting to it, meaning it should stay good for a long time.

An airtight container could be a box, Tupperware, or if you are on a budget, a Ziploc bag will also work.

Is it Ok to Use Expired Cornstarch?

Provided that you have managed to keep your cornstarch dry, you don’t really need to worry about the expiry date. Cornstarch doesn’t lose its potency or properties as it ages.

The expiry date on cornstarch is more of a mandatory legal requirement. All foodstuff must be labeled with an expiry date. Even if it has not got a chance of going bad.

Want proof?

Mineral water has an expiry date, yet it has taken thousands of years to filter through the rocks to get to the bottling plant… Lucky we caught it just at the right moment.

There are a few times when you don’t want to use expired cornstarch. If you see any of the following, then discard it and buy a new bag or box: –

  • If it has congealed or formed a solid lump, indicating the presence of moisture
  • If it is full of black flecks indicating that weevils have got to it
  • If there are blue, black, or green spots
  • If it has a strong acidic smell, again, this could be moisture. The smell comes from fermentation
  • If it is discolored. Dark brown or yellow cornstarch is a big no-no.

How Can You Tell if Cornstarch is Still Good?

It isn’t rocket science with cornstarch. Inspect it visually and take a pinch in your fingers. It should be fine without any course lumps. It should be almost pure white in color and, when mixed with water, should form a smooth paste.

Cornstarch shouldn’t smell of anything. Give it a sniff. If you smell dampness or mold, it is time to get rid. 

Can Bacteria Grow in Cornstarch?

Normally no. Bacteria need two things to thrive.

  • Food 
  • Moisture

While cornstarch ticks the ‘food’ box, without moisture, bacteria can’t flourish. So keep your cornstarch dry.

Should I Put Cornstarch in the Refrigerator?

You don’t need to keep cornstarch in the refrigerator. A cool, dry cupboard will be just fine. 


There is one exception.

Suppose you’ve mixed cornstarch with water in preparation for adding to a stew, soup, or casserole. In that case, it is a good idea to refrigerate it. If you don’t, the bacteria will begin to feast on the sugars in cornstarch. They also expel alcohol and carbon dioxide, so if your cornstarch paste is a little fizzy, it means that bacteria have begun to multiply, so make a fresh batch and discard the previously made paste. 

Related: Does hummus go bad?


Does cornstarch go bad? The answer is no, not normally. Provided you store cornstarch correctly, it has an almost unlimited shelf life. The only things you need to watch for are water and bugs. Now that you have found your cornstarch is still good, what are you going to make? Let us know in the comments below. 


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