SPECIAL REPORT: The Big Chill

The depths of winter seem like an odd time to talk about refrigeration. Most of us are in a deep freeze and fantasizing about tropical climes. But blast chilling is a special type of refrigeration that isn’t just for volume feeders anymore.

Not long ago, the primary purchasers of blast chillers were noncommercial operations either concerned about food safety or interested in implementing cook-chill systems to get greater efficiency out of staff and cooking equipment. Coupling tilting skillets and/or steam-jacketed kettles with large roll-in blast chillers enabled such operators to save on labor and food cost by cooking in large batches without losing food quality. The blast chiller’s ability to bring food temp down through the danger zone within 90 mins. also enhanced Hazard Analysis and Critical Control Point safety programs.

With the advent of midsize and smaller undercounter and countertop models, blast chillers over the last several years have started going mainstream. Several manufacturers even match the physical specs of their blast chillers to their combi ovens or those of sister companies now, making it easier to set up cook-chill systems for almost any size operation.

Safety First

Any operation that batch cooks at least some foods—soups, sauces, mashed potatoes, chili—or ends up with leftovers at the end of the night—roasted chickens, for example—can benefit from using a blast chiller. From a food safety standpoint alone, a blast chiller can pay for itself just in peace of mind, let alone in other costs.

Blast chillers, very simply, are designed to cool product very rapidly. In most cases, units chill foods from 160ºF or above down to 40ºF or lower in about 90 mins. The FDA Model Food Code says you have 4 hrs. to chill product to 70ºF from cooking temperatures, and an additional 2 hrs. to bring the internal temp down to 40ºF or lower, or 6 hrs. total.

What’s the big deal about those hours? Plenty. First, you increase your margin of safety by bringing internal food temps through the danger zone more quickly. Second, and related, by chilling food more rapidly, you actually increase its shelf life, giving you at least five days to use it in most cases.

The time saved often is labor saved. Staff doesn’t have to wait around at the end of a shift for product to cool before storing it in a walk-in. During a shift, employees can do something productive with the extra time. And, by cooking food in batches, you may be able to cook less often, also saving labor.

Quit Cookin’, Start Chillin’

Safer product is a higher quality product. Because blast chillers bring product temperatures down so quickly, they prevent bacterial buildup, which can degrade food quality along with making it potentially hazardous. Chillers also can prevent loss of moisture through evaporation, another enemy of quality. Depending on the product, blast chilling can give you a greater yield of anywhere from about 3% to 10% or more versus traditional cooling methods. 

Blast chillers essentially maintain the just-cooked quality of most foods, so when you rethermalize them they taste freshly prepared. The advantages are several. By preparing some foods during down time and blast chilling them for later service, you can expand your menu without expanding your kitchen. Even something as simple as sandwiches from a grab-and-go merchandising case can be prepared in advance and held for service. Blast chilling those sandwiches will give you crisper lettuce, juicier tomatoes and moist breads. And those sandwiches will stay fresher in the case longer.

If there are items on your menu that you prepare daily or several times a week, cooking them in larger batches less frequently and blast chilling them for later service can easily make your staff more productive and save you labor.

Learn The Lingo

Blast chillers can perform several different functions, but not all models do everything, so you need to find a unit that accomplishes what you want it to. And there are units on the market sold as “rapid chillers” that chill food quickly—generally from 160ºF to 40ºF in about 4 hrs.—but not nearly as quickly as blast chillers.

Hard chill. Blast chillers use the same principle as convection ovens, but in reverse—the polar opposite, you might say. They remove heat from food by rapidly circulating cold air through the cabinet. The colder the air and the faster it moves, the more quickly it strips away layers of heat from food.

The hard chill cycle typically refrigerates air to somewhere between 11ºF and 22ºF and circulates it rapidly until food in the cabinet is chilled to around 37ºF to 40ºF.

Soft chill. Soft-chill cycles use slightly higher temperatures of around 37ºF and often slower fan speeds to more gently chill delicate items such as seafood, pasta or desserts.

Blast freeze. Sometimes called shock freezing, this cycle is designed to bring food temps down quickly from around 160ºF to between 0ºF and -10ºF in 2 to 4 hrs. depending on the product. When food is frozen slowly, large ice crystals form and damage cells, which affects food taste, texture and quality. Blast freezing chills product so quickly that only micro-crystals form as the food freezes, resulting in higher quality when thawed and reheated.

Hold. Once a chill or freeze cycles has ended, most (but not all) models hold the product at the proper temperature until your employees are ready to remove and store it in a walk-in or reach-in. This cycle also can be used to thaw frozen products more quickly than simply leaving them in a walk-in.

Rapid chill. Though not covered in this article, it’s worth mentioning that a couple of manufacturers are producing refrigerated units that have more cooling power than a typical reach-in, but aren’t considered blast chillers. As mentioned above, these efficient rapid- or quick-chill models—some drawers and some reach-ins—are able to cool product from 160ºF to 40ºF in about 4 hrs.

Also not covered here in depth is a unit from one manufacturer that not only can blast chill or freeze a product, but also thaw and rethermalize it in the same box. It’s essentially a blast chiller and cook-and-hold oven all in one.

So what functions will you need? If you think you’ll use product quickly—within five days—or don’t have the frozen storage capacity, a blast chiller without the freezing capability may suit you just fine. If you plan on making some products like sauces only every so often and freezing them, you’ll need a blast freezer. If you plan on batch-cooking more delicate items like rice, pasta or seafood, you’ll need a model with a soft-chill cycle.

Another factor to consider is size. Most manufacturers still spec their capacity in terms of weight, but many also equate that to how many pans a particular model will hold. The reason for that is the performance of their equipment is based on how many pounds of food it will chill in 90 mins. or less. Obviously, the denser the food, the longer it takes to chill; it will take a 5-pan model longer to cool mashed potatoes than sole fillets.

As a general rule of thumb, figure 12 lbs. of food per 12″ x 20″ x 2½” hotel pan. So, a typical 5-pan model should easily chill 60 lbs. of food in 90 mins. or less; a 12-pan unit should be rated for 144 lbs., and so forth.

If you’re doing a lot of banquets or catering, you’ll probably want to consider a roll-in blast chiller that accommodates rolling racks or carts. Recently, a couple of manufacturers have introduced 3-pan countertop units that operate on 115V or 120V electric service, making blast chillers accessible and a smart alternative for even a small sandwich shop.

Power And Performance

Blast chillers, obviously, tend to be a lot more powerful than standard refrigeration equipment to cool down all that product in such a short time. Smaller 3-pan countertop or 5-pan undercounter models typically house ½-hp or ¾-hp compressors. Larger reach-in units are more likely to boast 1½-hp or 2-hp compressors, and roll-in chillers may have compressors as large as 4 hp or 5 hp.

One manufacturer has a unique 2-compressor system that uses both a larger and smaller compressor together to chill or freeze, and just the smaller compressor to hold food at the proper temperature once the selected cycle has ended.

Cooling power isn’t just a matter of compressor size, though. For example, the larger the condenser and the larger the fan, the more cooling the unit will provide. A couple of manufacturers use two fans to move more air through the cabinet and strip heat off the food more quickly.

Air movement, in fact, is important in a couple of key ways. The volume of air that moves through the cabinet has a lot to do with how fast product is cooled. But while cooling food faster helps it retain more moisture, paradoxically, blowing air across it can dry it out. How air is moved may be as important as how much air is moved.

Just as manufacturers have engineered different ways of eliminating hot and cold spots in convection ovens, most have their own solution to managing airflow in blast chillers. In a few models, air moves from front to back, but in most cases, air moves from one side of the cabinet to the other.

A couple of manufacturers use vents or louvers to move air in a circular pattern through the cavity to cover more territory more evenly. Another has vented the cabinet so air flows in a laminar pattern above and below the food pans that it claims strips away layers of heat more effectively.

Another maker has engineered its chillers so the fans pull air through the cabinet instead of pushing it through vents into the cavity. One advantage of the design, says the manufacturer, is that air pulled across the entire evaporator coil before entering the cavity is cooled more effectively.

Ultimately, as emphasized before, most models claim to pull down product temps to 40ºF in about 90 mins.or less. That’s well within HACCP and FDA Model Food Code parameters. But read the fine print. Some makers’ claims are based on a starting temp of 140°F, the minimum hot holding temperature in most health jurisdictions.

If you’re trying to cool a pan of stuffing with a recommended internal temp of 185°F or fruit pies hot from the oven with a core temp of 200°F, it might take a less powerful unit an additional 30 mins. to 60 mins.to pull down product to 40°F. That added time can affect how many production cycles you can fit into a shift or a day, so plan accordingly.

You’re In Control

Controls have gotten much more sophisticated in the past few years. At the same time, manufacturers have done a lot to make them simpler. Icons replace written instructions in many cases, and digital readouts (LED, LCD and even vacuum fluorescent) make it relatively easy to operate and troubleshoot most models. One maker just added a bigger color display to its units starting Jan. 1.

Blast chillers operate in one of three modes: time, product or probe. Not all models have all modes, but most have at least time and product modes. In the time mode you simply set the length of time you want the chill or freeze cycle to run and push a start button. The unit will alert you (audibly, visually or both) when the cycle is finished and/or automatically switch to a holding cycle.

In the product cycle, you select a product icon such as chicken and start the cycle. The blast chiller automatically selects the temperature to which it will pull down the product and the time it should take. Again, when the cycle ends the unit will hold the product at the proper temp and/or alert you.

Most models with a product mode also let you program in your own presets. Some models have about 20 programmable presets. Some controls let you program as many as 99 different chill cycles into memory.

The third type of cooling mode is done with a food probe. You insert the probe into the product you want to cool, close the door and press the start button. The chiller does the rest, automatically selecting temperature and time based on feedback from the temperature probe.

A couple of notes about models that offer probes: Some come with only one probe, but quite a few come with three. Three probes not only give you greater control, they also allow you to put three different types of products into the chiller. The probes will monitor how quickly the foods are being chilled (taking care not to freeze them if you’re only trying to chill them, for example).

When each pan of food is properly chilled or frozen, the probe will alert you, so you can remove that pan or the specific food if you have more than three pans in the unit. If employees are too busy to take food out of the chiller when it’s properly cooled, the unit will finish chilling the other product until the remaining probes are satisfied.

Probes from at least one manufacturer have three sensing areas for a more accurate picture of a product’s temperature on the surface, at the core and in between. This allows for more precise cooling, resulting in faster pull-down times and higher finished quality.

Probes for blast freezing from some makers are conical in shape, making it much easier to remove them from frozen foods. Another manufacturer has a probe that can be heated at the end of the blast-freezing cycle so it can be removed.

Finally, some probes are hardwired to the unit. Others, though, are removable, making it much easier to clean both the probes and the interior of the cabinet.

For The Record

Because a key function of blast chillers is food safety, most offer some form of HACCP record keeping. Until recently, many models featured an onboard printer that delivers a record of each chill or freeze cycle when it’s complete. One manufacturer features two printers on its models.

Many models now have a USB or other communications port instead of a printer. HACCP data is retained in the chiller’s memory until you download it onto a laptop, or in the case of the USB port, onto a thumb drive. Some makers who offer this feature also offer HACCP software that you can install on your computer. When you download the HACCP data, the software automatically loads it into a spreadsheet for tracking.

At least one manufacturer offers models with both an onboard thermal printer and a USB port, giving you the option of seeing printed reports immediately or waiting until the end of the day or week to download the data from memory.

On units with multiple probes, the HACCP memory typically records the start and end time and temperature for each probe, so you have a record of each product in the chiller. Units that allow you to select chill/freeze cycles by product type (e.g., chicken breasts or mashed potatoes) also will automatically note the type of product in the HACCP record.

And, for the record, make sure the racking system on the units you spec has pan slides or tray slides that will accommodate the hotel and sheet pans you intend to use. As mentioned earlier, some manufacturers design their blast chillers to complement their combi oven lines.

Ideally, the more flexible the rack system, the better. Some makers do offer a lot of flexibility, with slides that can accommodate both 12″ x 20″ hotel and 18″ x 26″ sheet pans. Some even have removable and adjustable slides, giving you not only greater flexibility over the combination of pans you can put inside, but making it even easier to clean the interior of the unit.

Some makers also offer you the option of similar-sized models in different physical formats. One maker, for example, has a 10-pan reach-in model that stacks pans vertically and another 10-pan model that is designed horizontally to fit under a counter or double as a worktable.

Care And Feeding

All blast chillers are built for durability, with stainless construction, and some go even further with small details like coated evaporator coils that resist corrosion from food acids.

Since blast chillers generate such cold temperatures, the evaporator coil will need regular defrosting, and the condenser coil may experience moisture buildup. Automatic hot-gas defrost is available on many models. Others use electric defrost that you can start manually. Models from at least one maker have an electric heating element to evaporate moisture on the condenser coil, too, so you don’t need a drain beneath the unit.

Like most refrigeration equipment, blast chillers don’t require a lot of maintenance other than regular cleaning. In addition to wiping down the interior and exterior daily with warm, soapy water (and a sanitizing solution, if required), keep the condenser coil free of dust and dirt. Never use chlorine-based cleaners as they can corrode even stainless, and use a flexible brush or a vacuum to clean condenser coils so you don’t bend fins.

Some models offer ultraviolet light sanitizing as an option. A UV light inside the cabinet helps kill bacteria and other microorganisms, but it doesn’t replace regular cleaning.

Many models have audible and/or visual alerts when a cycle ends or something goes wrong, such as a dirty condenser or evaporator filter, or temperature that drifts out of range. On models with more sophisticated electronic controls and displays, these warnings also are spelled out for you, often giving you ways to troubleshoot problems before a service tech needs to be called.

A Note About Energy

Since power and performance are important to blast chilling, this equipment isn’t the most energy-efficient in your kitchen. Energy Star doesn’t include blast chillers in its standards yet.

However, manufacturers have designed these units to be more energy efficient in several ways. Most now use thicker, better insulation. All use more energy-efficient fan motors.

One manufacturer uses centrifugal fans and scroll compressors to save energy. And a few models have a pre-cooling feature that brings down the cabinet temperature before hot food is inserted, so pull-down time is lessened, putting less stress on the compressor. And at least two manufacturers plan to introduce new models with improved technology at this year’s National Restaurant Association Show in May.

With all the choices on the market, you’ll find a blast chiller that suits your operation.