There's nothing quite like a quiet night on the couch, digging into a tub of delicious ice cream. Like so much else, engineering has a lot to contribute when it comes to crafting that perfect scoop. In fact, the ice cream-making process has many of the same challenges as other food production. Getting ingredients from the field to your fork might seem pretty straightforward, but there's actually a whole discipline dedicated to production, sanitation, transportation, and, of course, how it all tastes.

It's called food engineering. And the methods and techniques are every bit as high-tech as fields like aerospace or nanomaterial engineering. So, there's some food for thought.

[Intro]

It's no surprise that a lot of effort goes into maintaining the systems that make food, because everyone needs to eat. This is a place where engineers can make a big impact, and it's only going to become more important as the human population continues to grow. Whether it's ice cream or something else, engineering what we eat comes with a unique set of challenges.

Unlike a steel beam or a semiconductor, food tends to be perishable - in other words, it spoils. And, while people tend to be picky about what they eat, microbes like bacteria are much less fussy. They might already be in food, or they can easily find their way in through contaminated surfaces or the air. And, lots of those microbes love eating what we love eating.

That's not always a bad thing. Foods like blue cheese are purposely cultivated with certain kinds of bacteria to produce their distinctive flavor. But, most of the time, bacteria or viruses in your food are not good news. If the wrong kinds of microbes are growing on last week's pizza, odds are good that it will have a pretty nasty effect on your stomach. It could even lead to food poisoning. If food sits around longer, contamination becomes more likely. So, time is of the essence in food engineering.

From the time the ingredients are harvested to the moment the final product ends up in your bowl, there are lots of ways from contaminants to get into the mix and start causing problems. Exposing food to too much air, light, or the wrong temperature can also have adverse effects. A container of milk left on your porch in the sun too long will probably end up tasting strange.

So, engineers have to carefully control these aspects of food production that affect how easily bacteria can survive and how the food tastes. Accomplishing all this requires some of the other fields of engineering we've explored so far. Especially in the case of ice cream, our old friend thermodynamics comes into play.

To create cream in the first place, you have to separate it from raw milk. One way of doing this is with a centrifuge. Because of the difference in density between cream and the rest of the milk, the cream ends up farther from the axis of rotation in a spinning vessel, much like how swinging a pendulum in circles draws the heavier bit outwards. That cream can then be channeled away and collected.

Of course, other flavor-specific ingredients might require completely different production techniques. Consider the raisins you'd need for a batch of rum and raisin ice cream. As far back as ancient Rome, food production techniques took advantage of sunlight and wind to dry out fruits. Less water meant the fruits wouldn't spoil as quickly. Thousands of years later, the process hasn't changed an awful lot. Since the Sun is a readily available source of heat, many raisins are still produced by leaving grapes out to dry. And since the sugar stays behind as they lose water, raisins are sweet. 

No matter what ingredients you need for an ice cream flavor though, you need to mix them in large batches. Process control plays an important role in governing the ration of the ingredients and maintaining the machinery that transports them from one place to another.

You'll also need fluid mechanics, since the ingredients of mixtures like ice cream or cake batter are often in liquid form. You can use some of the same tools that might transport other liquids like petrol, but, again, everything needs to be sterile. And, you also need to consider the materials your equipment is made of.

For example,, microbes don't grow well on copper surfaces, so you might thank that would be great for preparing food. But, running a creamy mixture through a copper pipe might introduce bits of metal into the mixture. At best, it just ruins the taste, but, at worst, it could lead to heavy metal poisoning. Stainless steel, on the other hand, is particularly resistant to corrosion and doesn't lose a lot of material to the mixture.

So, say you have safe equipment to move your ingredients around. Next, the ice cream mixture, as well as flavor-specific ingredients like raisins or vanilla, will probably need sugar and emulsifiers to give it just the right texture.  In the ice cream production process, everything is combines in a tank, but it doesn't automatically mix evenly. To do that, you need to pass everything through what's called a homogenizer.

A homogenizer forces a fluid under high pressure through a small opening. That squeezing breaks down large chunks into smaller particles that are spread out more evenly for a smoother mixture. This mix of different ingredients makes the ice cream more viscous than cream alone. And, since the fluid is thicker, heat will flow through it rather differently than before.

That's quite important for what comes next: pasteurization. Pasteurization was invented by French biologist, Louis Pasteur. It involves heating foods, such as dairy products, and then quickly cooling them to kill off some of the bacteria. The resulting products then stay fresher for longer.

Because pasteurization involves a transfer of heat to the mixture, the ice cream's viscosity has to be taken into consideration when designing the machinery that efficiently heats it up. In the case of ice cream, you have two different options. One way is to apply a high amount of heat for about a minute. Or sometimes, large tanks can be heated at a lower temperature for a longer period of time. That changes the chemical nature of some of the ingredients, like caramelizing the sugar for example. It's up to the manufacturer whether or not they want that change in taste.

Once pasteurization is done, you need to bring the ice cream's temperature back down. And, crucially, you have to find a way to store it at that colder temperature.

Storage is a vital part of food engineering. Because of the shelf life of most foods, maintaining supply chains, which transport food between producers and retailers, is a tricky business. The clock is always ticking. But, the way you package it can buy time, which changes depending on the food. Bread has to be sealed in bags to avoid going stale, while foods like chopped tomatoes are best preserved in cans. And the storage environment at every step of the supply chain can also prolong the shelf life.

After pasteurisation, the best choice for your ice cream is to quickly move it from one freezer to the next until it's ready to be eaten. If it's going into a soft-serve machine, it passes through a single stage of refrigeration before filling the tank of the machine as a thick, cold liquid. Or you might want individual scoops in paper cups, pint-sized tubs for those long nights in, or the five gallon plastic bins used in restaurants.

Whatever you decide, once you've transferred the product to its final packaging, it needs some serious freezing. For ice cream, there are two stages that take place. The first is to harden it and the second is for storing it.

You might think anywhere below zero degrees Celcius would be fine. After all, water freezes at that temperature, so surely that's enough to stop any food from going off? Unfortunately, that's not the case. Depending on how soon it's going to be consumed, frozen foods need to be kept at a particular temperature. Frozen fruits, such as strawberries, can have a different shelf life depending on the temperature they're frozen at. Minus five degrees Celcius might allow them to keep for a month, but storing them at minus 25 degrees keeps them edible for two and a half years. As for ice cream, it needs to be kept at a chilly minus 40 degrees in storage. Any trucks that transport it and the storage facilities at the grocery store need to have a similar freezing capacity.

Blast freezers can achieve this by blowing cold air over the contents inside the freezer, carrying away even more heat than the kind you have at home. But after all that, you can head to the store and pick up a tub of your favorite ice cream flavor to store in your own freezer, ready to comfort you when needed. It really makes you appreciate the amount of work that goes into that spoonful of Cherry Garcia.

Of course, food engineering is about more than making desserts. The world's population is growing fast, and the demand for healthy, nutritious food will grow along with it. Equipment, such as freezers, mixing vats, and packaging machines all need to be specially designed for handling different products. The equipment needed for ice cream is different than the stuff for packaging fresh fruit or dried foods, like rice. Not to mention the engineering efforts that go into agriculture and supply chains.

To create and provide the foods we love, engineers will have to find ways to scale up delivery and production. All while ensuring that it remains free from bacteria and still tastes delicious. With a problem this big, even small improvements can result in vast savings of time, money, and energy, and that's a vital step towards a happy and well-fed world. Your nana would be proud.

In this episode, we looked at food engineering. We explored how food's capacity to spoil makes it a unique challenge from an engineering viewpoint. We saw how many branches of engineering come into play to process ingredients, ensure safety for consumers, and package food. As well as how thermodynamics is involved in the different stages of food production.

I'll see you next week when we explore the world of geotechnical engineering.

[Outro]

CrashCourse Engineering is produced in association with PBS Digital Studios. Want to keep learning? Check out Above the Noise, a show that cuts through the hype and takes a deeper look at the research and context behind the controversial topics in the news, hosted by Myles Bess. Subscribe at the link in the description. 

CrashCourse is a Complexly production and this episode was filmed in the Doctor Cheryl C. Kinney Studio with the help of these wonderful people, and our amazing graphics team is Thought Cafe.