One of the best things about summer is sweet corn. We’ve had it almost every night for supper this week. The two nights we didn’t, my kids whined like I just told them they have to give away their favorite toy. I don’t blame them though. What’s not to love about sweet corn? It’s not only delicious, but it’s fun to eat and fun prepare too. My kids love helping husk sweet corn. It’s a mess and takes longer than if I did it myself, but it’s well worth it. They have a blast, and I love the non-stop questions they ask. “What makes sweet corn sweet?” “Why does corn have hair?” “Is this the same corn that cows eat?” I usually give them pretty simple answers, but their questions got me thinking about the science behind the whys. Below are some of their questions, as well as questions about corn that I’ve been asked by students and teachers over the years.
What makes sweet corn sweet?
It’s all about sugar. Not cane sugar or beet sugar, but natural sugars that occur in plants. Sweet corn kernels have a very high sugar content when harvested at right time. I’ll go into more detail about this later.
What is the difference between the corn we eat (sweet corn) and animals eat (field corn)?
Although they are closely related, they look different, taste different and are used for different things. Sweet corn is a naturally occurring genetic mutation of field corn. The sweet corn plant is shorter, matures faster, and its kernels have a higher sugar content. Field corn is harvested in the fall, after the plant dies and the seeds are dry and hard. Field corn has a much higher starch content and is used to make livestock feed, ethanol, corn meal, corn starch, corn syrup and more. Check out our blog post from last year to learn more about the difference between sweet corn and field corn.
Is Iowa the top sweet corn producing state? If not, why?
Nope. Iowa doesn’t even make the top 20 list. Our growing season is too short and we are not home to any major canned or frozen vegetable companies. Sweet corn is only harvested in Iowa from July through early September. The fresh corn we eat the rest of the year comes from warmer states like Florida, California, and Georgia. Most of the frozen and canned corn we purchase is grown in Minnesota, Wisconsin, and the Pacific Northwest states. These states are home to many major vegetable processors who contact local farmers to grow sweet corn they use. Iowa’s landscape is covered with corn fields, but nearly all of it is field corn. Less than 1% of the corn grown in Iowa is sweet corn.
Why doesn’t sweet corn taste as good a few days after you pick it?
True sweet corn connoisseurs, including most farmers I know, prefer to eat corn the day it is picked. That is because it tastes better! When freshly picked, sweet corn is high in sugar and low in starch. As sweet corn sits after picking, the sugars in the kernel turn to starch. This mutes the flavor and affects its texture when cooked.
Having said that, it is completely safe to store in the refrigerator for up to a week. Be sure to leave the husks on until you are ready to cook it though. The husks help seal in the moisture and slow the conversion of sugars to starch.
Is sweet corn a fruit or vegetable?
Both. Botanically speaking, an ear of sweet corn is a fruit (the seed producing part of the plant). Tomatoes, squash, peppers and other seed-containing vegetables are technically fruits too. In culinary terms, corn is considered a vegetable because it is a relatively unsweet edible plant part. If you really want your head spinning with botanical lingo, check-out this fun video from SciShow. I think it is more entertaining than most prime-time TV, but I am admittedly a plant-loving science geek.
Why doesn’t sweet corn from the grocery store in the winter taste as good?
Corn purchased in the winter, is grown in southern states like Florida. It can be several days to a few weeks form the time it is picked until you buy it at the store. During this time, sugar in the corn converts to starch making it less sweet and tender. Growers and distributors store and transport corn in refrigerated units to slow this process, but there’s no way to stop effects of time completely.
What are the hair-like things between the husks and the kernels?
Although they are a big nuisance while cleaning and eating sweet corn, those “hairs” are extremely important. Corn kernels couldn’t develop without silks. In simple terms, the silk is a tiny tube that pollen travels down to make the kernels of corn. Corn is monecious, meaning it has both male and female flowers on the same plant. The corn silk is the female flower and the tassel at the top of the corn plant is the male flower. During pollination, pollen from the tassel is carried by wind to the silks. Pollen grains attach to the sticky end each silk, and then travel down the silks to fertilize each ovary. After pollination, the ovary develops into a kernel of corn at the other end of the each strand of silk. Take a look the next time you husk corn, and you will notice that there is a silk attached to each kernel.
How do farmers know when sweet corn is ready to harvest?
Sweet corn should be harvested at the milk stage. As the name implies, the kernels are full of a milky-looking juice when ready to pick. To test, growers will pierce the soft kernels with their thumbnail to look for the milk, or even bite into a raw ear to test for sweetness. Immature corn will ooze a clear liquid, while over-mature sweet corn kernels are tough and almost doughy inside.
There are also visual cues that you can use at the store without pulling back the husks. Ready-to-eat ears are plump. The silks at the end are brown and starting to dry, but the husks are still bright green and supple. Skinny ears with extra pointy ends and white silks are immature. These are signs that pollination just occurred and the kernels inside are not fully formed. Also avoid buying ears with completely dry silks and husks that are pale green, brownish, dry-looking. This indicates over-mature or not freshly picked corn.
Can you pick field corn early and eat it like sweet corn?
You can eat it, but it won’t taste nearly as good. Field corn also goes through a milk stage like sweet corn. As mentioned earlier, field corn has a much higher starch. This makes the kernels considerably less sweet and much tougher, even when harvested during the milk stage.
What other questions do you have? Ask away! I’d love to answer your questions and help simplify the science of sweet corn.
-Cindy
Iowa Agriculture Literacy 
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Great article. I found this through a Google search trying to find some info on a process that someone mentioned to me that I found interesting. Someone has suggested that if you leave corn with husk and silk in a grocery store produce bag, sealed, and at room temperature the corn will start to produce condensation in the bag and is actually sweeter than what it was initially. Do you have any thoughts on this?
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Sweet corn is going to be sweetest when it is fresh picked. It is best to eat it within two hours of picking if at all possible. The longer the corn sits off of the plant, the more of those natural sugars (fructose) will start to convert to starches. Starches won’t be as sweet.
If you can’t eat sweet corn picked straight off the plant, then there are some things you can do to try and recreate that sweet fresh-picked taste. The first thing I would recommend is leaving it in the husk. The husk serves as a natural protective layer. It reduces moisture loss and will slow down the conversion of sugar to starch. I’ve not heard of putting it in a produce bag before. I can’t speak to any science that might be involved in that. But it seems like the bag might simply provide an extra layer of protection. Corn produces chemical compounds as it sits – continuing to ripen and convert those sugars to starches. My theory is that by making the homeostasis environment smaller within the bag, the corn will slow down that chemical change. The condensation doesn’t really tell you anything other than prove that the corn is continuing to respire and release water.
Another trick that I’ve heard of includes adding a little bit of milk to the water as you boil and cook the sweet corn. Again there is probably some chemistry behind this. From personal experience, it seems to work.
And of course it is relatively common practice to salt the sweet corn when you eat it on the cob. Adding salt simply enhances and pronounces the natural sweetness of the corn.
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Thank you so much for the detailed answers. Are you in any Facebook food groups?
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We are slowly starting to get more active in some Facebook groups – emphasis on slowly. You can find us on Facebook at https://www.facebook.com/iowaagliteracy
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Does sweet corn get sweeter the longer it sits in the freezer? I did the whole blanching, shocking, kernel removal process and froze corn at the end of the summer. We have been eating it lately and it seems to taste more sweet than it did when we ate it during the summer. Am I just imagining that?
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Sara, I haven’t seen any research to suggest that sweet corn gets sweeter the longer it is in the freezer. From a scientific perspective, the amount of sugar that the corn has upon picking is the most that it will ever have. When you blanch the corn, what you are doing is stopping the respiration process – consequently stopping those sugars from converting into starch. So frozen corn should stay as sweet as fresh picked summer sweet corn. I might speculate that when frozen, some of the water crystals in the corn are slowly extracted. They might cling to the side of the corn or the side of the container. Left too long and this could result in freezer burn. But in the short term, what this might do is concentrate the remaining sugars in the corn. They are less diluted with natural water. This is only a hypothesis. The only way to know if frozen corn is sweeter is to do a side by side taste comparison and also measure the sugar content. But that experiment would be nearly impossible to set up because you have to have several months to freeze one sample. So….even if you are only imagining a sweeter taste…we say, just enjoy it!
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Thank you so much for the response! It does make sense about the liquid is extracted and thus brought to the outside more so it is the first thing you taste. I am going to go with that! LOL
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You say that sweet corn was developed in Pennsylvania and introduced to the market in 1779 but according to wikipedia “Sweet corn occurs as a spontaneous mutation in field corn and was grown by several Native American tribes. The Iroquois gave the first recorded sweet corn (called ‘Papoon’) to European settlers in 1779.[2] It soon became a popular food in southern and central regions of the United States.” – which doesn’t totally make sense because the Iroquois are in the northeast (in central NY state). I’m just trying to get my facts straight.
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Also found this (from the source on the wikipedia article quoted above) – The specific time when sweet corn originated cannot be pin-pointed; however, sweet corn was grown by the American Indian and first collected by European settlers in the 1770s. The first variety, Papoon, was acquired from the Iroquois Indians in 1779.
https://content.ces.ncsu.edu/sweet-corn-production
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Nice research! Yes, sweet corn is a natural mutation of field corn. For commercial purposes, native farmers had to isolate the seeds that displayed this natural mutation to ensure that the entire field yielded sweet corn – not just a few random mutations. If you follow the wikipedia citations, it links to the same research from North Carolina that our article linked to and the one that you cited.
The Iroquois nation was primarily in what is now modern day New York. But throughout the 1700s Iroquois tribes controlled territory south into modern day Pennsylvania. Specifically, Iroquois tribes that lived in Pennsylvania were the Erie and Susquehannock (not part of the Iroquois League and Six Nations, but still spoke Iroquoian and had similar cultures). And they traded with other tribes as far south as modern day Kentucky. So there is bound to be some lack of specificity. The Iroquois can be credited with providing the first sweet corn variety, but sweet corn had been worked on and perfected for maybe as many as 80 years before by many native and later European farmers.
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Will wet rainy weather wash the sweetness from corn?
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Dan, All of the sweetness is found inside each kernel of corn. So it is a myth that rainy weather will wash away the sweetness. However, with an abundance of rain the plant may absorb more water in the growing process. The sweetness might become slightly diluted as each kernel fills up with just a little extra moisture. But the plant should balance it self out again once the rain stops. Remember, sweet corn is still actively growing before and after it is picked. It has a tendency of changing from one day to the next based on the environmental conditions (dry, wet, hot, or cold).
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Iowa is as much a fantastic place to grow sweet corn as it is to grow field corn. In fact, the most naturally prolific stands of sweet corn I have ever seen have been in the heart of the “corn belt.” That is no accident. The season is plenty long (think about much of it in Iowa coming from Minnesota…); it’s just that the commercial processors and marketing mechanisms aren’t available and viable compared to other areas. If you are familiar with sweet corn production in CA, the Northwest, and elsewhere, you know that Iowa could put most of them out of business on an inputs-cost basis if Iowa farmers really wanted to focus on that. They are less advantaged as a rule, not more. They’re just there for customer ease of access.
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What is the biochemical bases and procedure of preserving sweet corn
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Sorry…can’t help you with the biochemical bases part of your question. We aren’t experts in chemistry. But I can tell you that procedures for preserving sweet corn can vary widely. The two main methods are canning and freezing. For both you start by cutting the kernels from the ear. Some people blanch it and then freeze or can it. I would recommend looking for a recipe to follow and then do some experimenting yourself. I haven’t found one perfect method.
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Is it possible to convert field corn to sweet corn by applying physical treatment, such as soaking in sulphur or another chemical element?
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Field corn and sweet corn are genetically different. So, no, you can’t apply a physical treatment to make field corn turn into sweet corn. That said, field corn produces many of the same sugars early in its development. If you pick and eat it at just the right time it will taste sweet – very similar to sweet corn. But identifying when to pick it is really hard. Those sugars quickly turn into starches as the plant matures and won’t be sweet. The two crops are bred for different purposes – sweet corn to be picked fresh and eaten and field corn to be picked dried and stored for use later.
For a fun chemistry experiment, try putting a little bit of corn starch (corn flour made from field corn) onto your tongue. At first it will be dry and maybe a little bitter tasting. But after a few minutes it will start to taste sweet. That is because the amylase enzymes in your saliva are breaking the starches back into simple sugars. Your tongue will recognize the sweetness of the sugars. The plant works hard to produces sugars and turn them into starches. Then enzymes in your saliva basically reverse that process.
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I work at a local grocery store. The management of the store insist we trim the corn, pulling off the dark green leaves from the husk and trimming the silks off the top before we place it in the bin. I have long argued that this is a waste of time and that pulling off the dark green leaves and cutting the silks will cause the corn to dry out faster. I feel the corn will stay fresher, sweeter and moisture if left alone. Management has advised me that there was a memo sent out requiring us to cut the silks off saying that the silks dry out the corn. Please tell me, who is right
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We’re going to side with you! The green husks are a natural protective layer that will help keep the moisture in the corn. They should only be removed at the last possible moment for maximum quality. I have not read anything that would suggest that the silks will dry out the corn. They are probably just observing the natural process. But the silks don’t speed that natural process.
Many grocery stores do choose to remove the husk, leaves, and silks. This is for two reasons – aesthetics and consumer easy. Having the bright yellow cobs visible rather than the green husks may be more appealing to customers and therefore may sell more corn. Having the husks removed also makes it easier for customers as it is one less thing for them to have to do when they get home. In the end it is customer preference…do they want the highest quality produce or do they want ease and convenience.
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I work at a local grocery store. The management of the store insist we trim the corn, pulling off the dark green leaves from the husk and trimming the silks off the top before we place it in the bin. I have long argued that this is a waste of time and that pulling off the dark green leaves and cutting the silks will cause the corn to dry out faster. I feel the corn will stay fresher, sweeter and more moist if left alone. Management has advised me that there was a memo sent out requiring us to cut the silks off saying that the silks dry out the corn. Please tell me, who is right
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Thank you so much for this informative article! I’ve got a question about the parts of a corn kernel and their impact on flavour/texture (in, say, a blended corn soup): the outer skin/cover of each kernel seems to be called a pericarp, and I wonder, does it bring any flavour to the party? Or is that all from the insides it’s holding? (I would assume the pericarp is high in fibre, so there’s that.)
Thanks in advance!
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Corn isn’t a vegetable or fruit; it’s a grain, like rice. The seeds of a grass plant: grain. 🌽😊💛
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What’s the ideal time to boil sweet corn to change starches to sugar? Does the different sweetness levels change the boil time? And does microwaving corn change starches to sugar?and what would be the ideal to microwave?
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