A Field Guide to the North American Cold Chain

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So far in the “Field Guide” series, we’ve mainly looked at critical infrastructure systems that, while often blending into the scenery, are easily observable once you know where to look. From the substations, transmission lines, and local distribution systems that make up the electrical grid to cell towers and even weigh stations, most of what we’ve covered so far are mega-scale engineering projects that are critical to modern life, each of which you can get a good look at while you’re tooling down the road in a car.

This time around, though, we’re going to switch things up a bit and discuss a less-obvious but vitally important infrastructure system: the cold chain. While you might never have heard the term, you’ve certainly seen most of the major components at one time or another, and if you’ve ever enjoyed fresh fruit in the dead of winter or microwaved a frozen burrito for dinner, you’ve taken advantage of a globe-spanning system that makes sure environmentally sensitive products can be safely stored and transported.

What’s A Cold Chain?

Simply put, the cold chain is a supply chain that’s capable of handling items that are likely to be damaged or destroyed unless they’re kept within a specific temperature range. The bulk of the cold chain is devoted to products intended for human consumption, mainly food but also pharmaceuticals and vaccines. Certain non-consumables also fall under the cold chain umbrella, including cosmetics, personal care products, and even things like cut flowers and vegetable seedlings. We’ll be mainly looking at the food cold chain for this article, though, since it uses most of the major components of a cold chain.

As the name implies, the cold chain is designed to maintain a fixed temperature over the entire life of a product. “Farm to fork” is a term often used to describe the cold chain, since the moment produce is harvested or prepared foods are manufactured, the clock starts ticking. The exact temperature required varies by food type. Many fruits and vegetables that ripen in the summer or early autumn can stand pretty high temperatures, at least for a while after harvesting, but some produce, like lettuces and fresh greens, will start wilting very quickly after harvest.

For extremely sensitive crops, the cold chain might start almost the second the crop is harvested. Highly perishable crops such as sweet corn, greens, asparagus, and peas require rapid cooling to remove field heat and to slow the biological processes that were still occurring within the plant tissues at the time of harvest. This is often accomplished right in the field with a hydrocooler, which uses showers or flumes of chilled water. Extremely perishable crops such as broccoli might even be placed directly into flaked ice in the field. Other, less-sensitive crops that can wait an hour or two will enter the cold chain only when they’re trucked a short distance to an initial processing plant.

Many foods, including different kinds of produce, fresh meat and fish, and lots of prepared meals, benefit from flash freezing. Flash freezing aims to reduce damage to the food by controlling the size and number of ice crystals that form within the cells of the plant or animal tissue. Simply putting a food item in a freezer and waiting for the heat to passively transfer out of it tends to form few but large ice crystals, which are far more damaging than the many tiny ice crystals that form when the heat is rapidly removed. Flash freezing methods include cryogenic baths using liquid nitrogen or liquid carbon dioxide, blast cooling with high-velocity jets of chilled air, fluidized bed cooling, where pressurized chilled air is directed upward through a bed of produce while it’s being agitated, and plate cooling, where chilled metal plates lightly contact flat, thin foods such as pizza or sliced fish.

A Field Guide to the North American Cold Chain

What’s A Cold Chain?

Big and Cold

Reefer Madness