The Science of Popcorn delves into exactly this, in Adrian Pennington's debut CT article

The Science of Popcorn...

Adrian Pennington, Freelance journalist

We know about every technical advance that enhances the movie-going experience, from digital projectors to multidimensional sound systems. But what about the cutting-edge technology that goes into creating the world’s favourite cinema snack?

We’ve been to Dolby to see how they build their range of products and what they achieve is truly incredible. But there is just as much, if not more, technology and R&D in popcorn than in any other aspect of the movie theatre,” says Thomas Peace, International Sales for Nebraska-based farming collective Preferred Popcorn.

What would movies be like without this salty, buttery snack? Americans alone consume 16 billion quarts of the stuff every year. Two thirds of this is consumed at home, and a third in the cinema and at other events like baseball games, according to the Popcorn Board.

For cinema owners, the humble puffed snack, whose popularity grew during the Great Depression when it was an inexpensive meal, is a revenue lifeline. For years, the exhibitor business model has been built on ticket price plus concessions; one without the other means swiftly going out of business.

When it comes to popcorn, cinema owners want a seedto-snack treat that leaves more snacks than seeds when popped. This means when the corn is popped at the concession stand, there shouldn’t be many unpopped kernels left in the popper. Very few have the space to store kernels at any volume.

The agronomics (the science of soil management andcrop production) behind this are incredibly sophisticated. The major factors that influence popcorn quality, and ultimately exhibitor profit, are kernel moisture, expansion ratios, and popping ratios.

We talked to Preferred Popcorn about their process and also leaned on another cornbelt supplier, AK Acres (akacres. com), as well as industry veterans, Cretors (cretors.com), inventors of the popcorn machine, to learn more about thefield-to-forum process, which all starts in the lab.

The Raw Ingredient

Not all corn is popcorn and not all popcorn is created equal. Popcorn is a specific type of corn kernel which expands and puffs up when heated. The fundamental science - which pre-Inca cultures knew the basics of (enough to chuck the seeds in a fire) - is that the kernel’s strong hull (pericarp)contains the seed’s hard, starchy shell with 14-20% moisture. This turns to steam as the kernel is heated. Pressure then builds until the hull ruptures, allowing the kernel to forcefully expand, from 20 to 50 times its original volume.

Within the popcorn family there are many different hybrids. These are obtained by cross-breeding different strains of popcorn to emphasise specific characteristics in the corn after it is popped. Such characteristics include the size, shape and texture of the kernel but the main desired attribute is its expansion rate.

Most corn when it pops takes on an irregular shape and is referred to as ‘flake’ or ‘butterfly’ popcorn. Others take on a more rounded shape and are referred to as ‘ball’ or ‘mushroom’ corn. Yellow popcorn is the most commonly used for commercial applications since it is less fragile than the white version mostly consumed in the home. The kernels are rounded in shape and have a medium brown colour. Within this group there are several options available to the buyer.

Years in the Making

Preferred Popcorn grows 25 different genetic variations to meet the needs of its customers. “That starts with yields of sampling from which we test over 100 different varieties and narrow it down to make sure we’re growing the best crop,” Peace explains. “If you genetically modify it, you change the genetic code of the popcorn and get the attributes you want in one year,” he says. “We do not do that. We employ doctoratelevel biologists to help us selectively breed over many years to achieve the attributes we want. Each variety has a specific use and a specific customer in mind when we grow it.”

Popcorn hybrids with a thicker protective outer seed coating have a greater expansion ratio but this is not the only important trait. Other variables include grain yield, kernel length, popping expansion, kernel and protective layer thickness, heat transfer ability, and the amount of protein in kernels. Understanding which popcorn traits are related to the expansion capacity will help processors identify and breed high quality popcorn. The moisture content of the hybrid will also determine the expansion of the popcorn. In addition, cracks and abrasion on the outside of the kernels will reduce popping expansion; which is what both breeding and processing is designed to weed out.

Popcorn Expansion

This is the heart (kernel?) of the whole popcorn industry. Different varieties will produce different sized and shaped pieces of popcorn when popped, which has an impact on the cinema owner’s profit. This percentage variance can be quite significant which is why processors go to great lengths to grow varieties with the right (pop-for-buck) ratio.

Expansion level is the key metric. This is the amount of growth in volume that the corn goes through in the popping process. In general, the more the corn expands the better the product. High expansion corn is desirable for both the consumer and the manufacturer. From a consumer’s point of view high expansion corn is more tender and has fewer partially popped kernels that are hard to chew.

The theatre owner buys popcorn by weight and sells it by volume (in a box or bag). High expansion translates directly to increased profitability. Each percentage point of increased expansion is a reduction in raw material cost.

“If you’re a cinema owner you want as much volume out of that bag as possible because it means you can sell more servings,” says Peace. “The expansion level is very important. It is written into all the contracts we have for major cinema owners.”

Expansion is measured as a ratio that compares the number of popped popcorn servings produced from a specific amount of unpopped popcorn. The test is performed with a Metric Weight Volumetric Test (devised by Cretors - and they also make the MWVT machines) and the test is recognised as standard by the popcorn industry.

For example, an expansion of 42:1 means that 1 gram of unpopped popcorn will produce approximately 42 cubic centimetres of popped popcorn. The higher the MWVT number, the greater the volume of popped corn per weight of unpopped corn. A typical rate would be 42-44.

The customer usually equates high expansion corn with high quality. For the manufacturer, high expansion will create a physically larger bag for the same weight and may be considered better value by the customer. High expansion corn also usually indicates a low percentage of unpopped kernels or scrap. In this case corn is not only purchased by weight but also sold by weight.

From Field to Customer

One of the largest contributors to popcorn quality is the processing that the corn is subjected to after being picked. Much of this is automated.

Raw Popcorn Harvesting

The popcorn is processed using advanced milling and cleaning equipment to remove any foreign material such as broken kernels, corncobs, and dirt. There are several stages to this:

A screen cleaner uses shaking screens and highpowered blast fans to remove the large pieces of foreign material and field corn as well as smaller containments like weed seeds, immature or broken kernels, and dust.

A gravity table or destoner removes impurities on the basis of density. A gravity table uses high volume fans and a shaking perforated deck to suspend the popcorn above it on a cushion of air. The angle and shape of the deck causes the popcorn to move to different ends of it, depending on the popcorn’s density. Broken, cracked, and immature kernels move towards the back of the machine where they are removed, while all of the good kernels move toward the front of the deck and exit the machine. Some machines have magnets to remove metal.

A computerised colour sorter uses advanced highresolution optics to visually inspect each kernel of popcorn as it flows through the machine at a rate of 20 metric tonnes every 45 minutes. That’s every single kernel. Doing that manually would clearly be an impossible task but the most up-to-date machines can identify imperfections such as discoloured kernels using an AI algorithm and infrared light to check inside each seed. Defects are removed by a jet of air.

The colour sorter at Preferred Popcorn snaps a picture of each kernel and stores this image. Says Peace, “We can program the machine to look for red kernels, for example, and we can analyse the results to input into our breeding process.”

This phase is not just about removing visual defects or physical debris, it is also about removing chemicals like insecticides, pesticides or fertiliser that could have contaminated the harvest from a neighbouring field.

“We are continually testing to make sure these things are not in our process,” says Peace, who emphasises the stringent food regulations that are required to sell Preferred Popcorn products in markets like Japan and Germany.

“We are organically certified, non-GMO, halal and kosher,” he says. “All of that plays into how we design our plant.” Clean corn is then sent to packaging on pallets for shipping, or stored in huge silos.

A Focus on Sustainability

Green farming practices are encouraged, if not universally followed or mandated. Preferred Popcorn says its farmers deploy crop-rotation, soil- and water-testing and minimal use of fertilisers. It employs ‘no-till’ farming which reduces soil compaction (to give next years’ popcorn roots air to breathe) and also reduces the number of passes through a field, thereby reducing carbon emissions and encouraging microbiological soil development.

“We save valuable resources by gathering samples of the soil to more deeply understand which nutrients are missing,” Peace says. “With that information, we’re able to use precision GPS-monitored applications of fertilisers and use pesticides and herbicides only as needed to control crop issues. We are also testing new technology with nitrogen uptake enhancing microbes to reduce or eliminate synthetic nitrogen enrichment, which results in cleaner air and water for our communities.”

Moisture Content

Popcorn is usually delivered to the user with moisture content between 13.5% and 14.5% - because that’s when it pops best. The actual moisture content will depend on the variety and what the processor determines will give the popcorn maximum expansion when popped.

“Popcorn kernels are a little bit like a sponge,” says Peace. “If the ambient humidity is 60% or higher, the popcorn will absorb moisture, possibly causing it to go mouldy over time. If the humidity is 50% or less, the popcorn will dry out, hindering its ability to pop.”

Popcorn is normally harvested with a moisture content of 14% to 17%. According to AK Acres, popcorn harvested below 14% moisture may be too dry and may not pop well. But popcorn harvested above 17% may be too wet and may spoil when stored in grain bins.

Storing Popcorn

Consequently, monitoring of the moisture in storage is critical. Kernels can be stored almost indefinitely as long as the moisture level does not change. Silos are equipped with computer-controlled aeration systems that continuously monitor air humidity and temperature. AK Acres programs its computers to turn large aeration fans on or off to keep the moisture at the optimum level. Natural air-drying, as opposed to natural gas heat, preserves the seed coat integrity and the appearance of the popcorn for customer satisfaction and maximum expansion potential.

Preferred Popcorn keeps all its varieties in separate storage. Storage is incredibly expensive, says Peace, partly because of the constant monitoring, and partly because of the space it needs.

“Some companies don’t have the storage so they grow and sell it off in the first couple months after harvest. But storage is expensive for the customer too. We choose not to put the burden on the customer. Our customers tell us how much they need for the next year, we grow that volume and the kernels stay with us until they tell us they need it. That’s when it’s cleaned, packaged and shipped.”

Butterfly or Mushroom?

Butterfly kernels are the most common type of popcorn, tending to be large and fluffy with many ‘wings’ protruding from each kernel. The mushroom kernel is more compact and is shaped like a ball – ideal for processes that require heavy handling of the kernels such as sugar coating.

“A high expansion butterfly popcorn has really big wings which is great as long as it’s not handled a lot. In a cinema setting that’s perfect since the popcorn is popped and (ideally immediately) scooped into a bag and delivered to the customer,” Peace explains.

“If you take that high expansion butterfly corn, pop and season it, put it through a packaging machine, in a box on a truck shipped to a store then handled again, those wings will break off. That is how you get a bag that’s one third full. So, you can use a low expansion popcorn and it’s why we breed it for certain customers. It’s simply much hardier when handled.

“Some customers in retail settings like a grocery store might have a 1kg bag with their brand name on it. What matters to them is they want the unpopped kernel to look beautiful, to be big, bright, orange and clean-looking since this is what they are selling to their customers. So, we breed a variety for how the unpopped kernel looks.

“With mushroom corn there are also customers offering gourmet popcorn who care about the uniformity of large round balls because they want theirproduct to look good in a bag. Theydon’t care about expansion if it fills abag. What is selling their popcorn is itsvisual appeal.

“Other customers are catering to patrons who tend to like sugarypopcorn so it’s important that the popcorn won’t fall apart ina tumbler as seasoning is added. Mushroom is the key here.The thing about most mushroom popcorn is that it does noteven get close to the expansion level of butterfly. It’s at the23-30 levels rather than the 44-45 level. However, one SouthKorean cinema customer of ours wants a mushroompopcorn with a high expansion level. We have bred, andgrow, a special variety that just goes to them with a pop levelclose to 40. That is a unique variety that will coat well but hasa high expansion level.”

Sit Back and Enjoy

Believe it or not we’ve barely touched the sides of thepopcorn industry. Contrast a new 3D 4K digital projectorwhich might cost $100,000 with the latest combine used toharvest fields at over $500,000. Hopefully, we’ve given agreater appreciation for the level of research, innovationand engineering that goes into getting the perfect popcornto your cinema seat.

Why Popcorn Pops

A popcorn kernel’s very hard hull (pericarp) is capable of withstanding an internal pressure of 135 PSI (9.1 atmospheres). The starch in a kernel is a hard starch containing about 14% moisture. When heated, the pressure and temperature in the kernel rise, cooking or gelatinising the starch. At about 135 PSI (9.1 atmospheres), the pericarp ruptures and the pressure is released, the water expands to steam and stretches the starch cells to many times their original volume so they take on a foam structure.

As the steam is vented to the atmosphere, the pressure drops to atmospheric pressure. As the pressure drops so does the temperature. At the lower temperature the starch returns to a solid state but is now in the form of an open-cell foam, giving popped popcorn its crispiness.

The actual popping process requires a delicate balance of heat rate and moisture content. If the kernel is heated too quickly the starch at the centre of the kernel is not gelatinized and softened. The starch at the outer edge reaches the required temperature and causes the pericarp to rupture but the uncooked starch at the centre of the kernel does not expand. The result is a small hard partially-popped kernel of corn. But if the heat process is too slow, the build-up of internal pressure cannot keep up with loss of moisture as steam vents from the tip of the kernel.

Heating the kernel must be at a slow enough rate to cook the starch to its core, before internal pressure ruptures the pericarp; but not so slowly that the small amount of moisture available leaks out before the kernel reaches popping temperature and pressure.