Learn the science behind:
Grilled corn on the cob, cornbread, popcorn, corn tortillas, none of these would exist if there had been no corn. But did you know that they all rely on slightly different types of corn? There are a lot more corn varieties under the sun than your standard yellow corn cobs, that you might find in your (super)markets.
All corn varieties, and there are a lot, belong to the Zei Mays species. Within that one species, there’s a lot of variation. Just some of the aspects in which they can vary:
- Size of the cob, some are only a few centimeters long, whereas others are 20-30 cm in length.
- Color of the kernels, from red to white to yellow, speckled or just one color, corn can be a lot of different colors!
- Sugar content: some varieties only contain a small amount of sugar whereas others have been bred to contain very high amounts of sugar.
- Starch content: this is closely related to the sugar content, both the amount of starch as well as the type of starch can vary widely between corn varieties.
These differences make some corn varieties best suited for eating fresh, whereas others truly need to be processed extensively before eating. Over the years, humans have bred corn varieties to suit their needs. Simultaneously, we humans have adopted ourselves to different corn varieties, by developing different ways to use and eat them.
The different varieties do have several characteristics in common. First of all, corn always grows on a cob, which may be protected by leaves. The whole cob is full of corn kernels, that all attach to the center ‘pole’. The cobs attached to a central stalk of the corn plant. Some varieties only grow one cob per plant, others might grow several.
Corn needs to be planted every year, it’s an annual crop. Once the cob with corn has formed the initial kernels will be sweet and juicy. Over time, as they grow older, they become more starchy and less sweet. Also, their outer protective hulls become firmer and tougher over time. You will notice below that some varieties will be harvested early, to have those sweet and juicy kernels. Others though will be harvested way later, to ensure the kernels have become more starchy and firm!
The most visible corn variety is sweet corn (Zea mays convar. saccharata var. rugosa). Whether it’s corn on the cob, corn in a can, or frozen corn kernels, they’re all sweet corn. What’s interesting about sweet corn is that how we eat it, is more like a vegetable, than a grain. On the other hand, when used to make tortillas or cornbread, we treat it more like a grain, as we would wheat flour.
Sweet corn is harvested relatively early in the corn growing cycle. You want to cobs to be juicy and sweet. Once the corn has been harvested
As the name says, sweet corn is sweet. It has a higher sugar content than most other corn varieties. Over the years the corn has been bred for this specific characteristic. There are a lot of different sweet corn varieties, but there are a few ways to group them:
- Sugary 1: this is quite a sweet variety of corn with a high amount of sugar. If you dry this variety it shrinks considerably. Until the early 1960s, this was what sweet corn was.
- Supersweet: this corn variety is considerably sweeter and is what you might find in your supermarket. An added advantage is that it stores very well, while remaining sweet.
- Sugary enhancer: this is yet another sweet variety, with a higher sugar content at the point of harvest
Cornbread and Polenta corn
Next up is corn used for making cornbread and polenta. The big difference compared to sweet corn is that you want to convert this corn into a flour by milling the corn kernels. This is done through dry milling, which is similar in process to how wheat is ground. As such, you’re not looking for a juicy corn kernel, instead, you’re looking for a sturdier, drier kernel with a strong enough husk. The corn should crack and break in the mill, instead of becoming deformed or stretched apart. Of course, the kernel shouldn’t be too hard either. If it’s too hard it won’t perform well when used for baking or cooking. The cornmeal won’t be able to absorb moisture as well for instance.
Since these kernels should be hard, not juicy, this corn needs to harden out and dry. As such, farmers will harvest this corn a lot later in its growth period than they would for sweet corn. Also, they’d choose a corn variety that is naturally harder and better suited for milling. In the US (one of the biggest corn producers), a commonly used corn for dry milling is yellow dent corn.
Individual corn kernels can have a strong hull that’s not well digested by humans. Hundreds, if not thousands of years ago, people in the Americas realized that they needed to find a way to handle this tougher hull. A method that has since spread widely is to use of lime (a very alkaline ingredient) to process the corn hulls. People discovered that by soaking or cooking corn in this alkaline environment the hulls would soften and can be removed a lot more easily than through pounding the kernels.
This process, called nixtamalization, lies at the core of making corn tortillas and many other dishes. It so happened that this process also improves the uptake of vitamin B from corn. As a result, it prevented diseases such as pellagra in areas where people were heavily dependent on corn. It also changes the flavor of the corn, which is why flour made from nixtamalized corn will taste different than ‘regular’ cornmeal.
Whereas you can nixtamalize a lot of different types of corn, manufacturers look a for a hard corn variety. Again, it shouldn’t be too hard, or the cooking time in alkaline liquid will take too long. Also, manufacturers will look for a corn where the outer hull loosens from the center easily. This is also variety dependent. Dent corn is often used for nixtamalized corn, but there’s a wide variety of variants that are outside outside of this group as well.
Last, but not least, popcorn corn. Popcorn corn is successful when it can be popped. Not every corn pops, fresh sweet corn for instance won’t. Popcorn corn is a very specific corn variety: Zea mays var. everta. This type contains a lot of starch (which is what fluffs up) and not too much sugar. A strong husk on the outside is very important as well. It should be strong enough for the pressure to build up inside that enables the popping of corn.
Sign up to our weekly newsletter to be updated on new food science articles.
Whereas sweet (regular) corn is harvested at its sweetest and still very moist, popcorn is harvested at a much later point of its growing cycle. The corn is left on the stalk to dry out after ripening. This hardens and dries the corn, which will help it pop since it will be possible to build up some pressure inside the corn. During harvest farmers need to be careful. The hull should not be damaged or it can’t serve as a pressure vessel anymore.
One of the factors farmers and manufacturers test for on popcorn corn is its expansion rate. Just how many times bigger is the volume of the popped vs. unpopped corn.
Mixing it up
With the exception of popcorn, there are a lot of different corn varieties per application and there are plenty of varieties that can be used for more than one application! All have their own characteristics and strength and grow well in different regions. This last aspect is very important. You want crops that are well adjusted to their growing region to get optimal growth and harvest. A good amount of diversity in varieties will only make our agricultural system stronger and our stores more interesting!
Anthony Boutard, Beautiful Corn, 2012, link
Caleb Pershan, Where does your popcorn come from?, 2014, Modern Farmer, link
Maricel Presilla, Gran Cocina Latina, 2012, p.233-257
Jennifer Poindexter, Growing Corn: Varieties, planting guide, care, problems and harvest, Morning Chores, link ; if you’re looking for specific corn varieties to plant, this article gives several examples, though is US focused
Patrick, Corn Tortillas Made From Popcorn Kernels, Mexican Please, Oct-9, 2020, link
Rooney, LW., Serna-Saldivar, Sergio O.. Tortillas: Wheat Flour and Corn Products. United Kingdom: Elsevier Science, 2015, table 12.1
Science and Technology of Fibers in Food Systems. Switzerland: Springer International Publishing, 2020, p.95
C. Wayne Smith et al, Corn – Origin, History, Technology, and Production, 2004, Chapter 2 & 4, link