Ice cream’s toughest opponent - The Heat Shock Effect

There’s nothing worse than losing control over the quality of your ice cream – particularly when it left your factory in perfect condition, on its way to what you had hoped would be a perfectly satisfied consumer.

Out-of-control quality is, however, a reality for all too many ice cream manufacturers whose precious products are subjected to temperature fluctuations between the factory and the dinner table. With the right blend of emulsifiers, stabilisers and know-how, however, quality ice cream can be helped to stay that way – and customer satisfaction maintained or even increased.

Ice cream at risk

Of all the frozen food types, ice cream is the most sensitive to temperature fluctuations. If not kept frozen at very close to its ideal storage temperature of -18 to -25 °C (-0.4 to -13°F) from one end of the cold supply chain to the other, it can suffer severe damage, including changes in flavour, colour, texture, smoothness and even the state of packaging.

• Ice cream is affected in two key ways by temperature changes:
• As temperatures rise, ice crystals melt and air cells collapse, and neither of these effects can be restored by lowering the temperature again.

As temperatures fall again, ice crystals build up in size (although never increasing in their total number) and lactose crystals form, lending a sandy sensation to the consumer’s eating experience.

The final result of the Heat Shock Effect is shrinkage, gritty ice crystals and sandy lactose crystals. In fact, after being in contact with warmer air for just a few minutes, ice cream will start to thaw – even though the product may still appear frozen! When again subjected to the correct temperature, the product will freeze slowly because typically, equipment in the cold chain is designed to maintain product at -18°C (-0.4°F) rather than to freeze the ice cream down to this temperature. Slow freezing creates large ice crystals, damaging the product’s structure and mouth-feel.

Weak links in the cold chain

The Heat Shock Effect may already appear from the moment finished products sit on the factory’s loading dock. Where the manufacturer has stringent quality control, such damage affects only a small percentage of shipments. For those not deploying best practices, however, or whose staff lack a culture of strict compliance, noticeable damage can already be done at this early stage. And in hot climates, of course, even the slightest of delays can have far-reaching consequences.

Transport hot points

The next Heat Shock ‘hot point’ concerns the trucks that transport the ice cream to distribution points or directly to retail outlets from the manufacturer’s loading dock. The problem here is that the refrigeration systems of such trucks are often incapable of maintaining a strict temperature level, instead fluctuating between -17° and -20°C (0° and -4°F). Further, heat can get into the storage compartment, reaching the product itself through the vehicle’s insulation or via air leaks in badly sealed doors. And the ingress of water is yet another factor that has quality control experts feeling less than secure.

When the truck’s cargo doors are opened to make partial deliveries, the temperature may rise for goods stored closest to the opening, depending on a number of factors such as the quality of the packaging, the length of time the door is open, and the temperature outside. And transfer points – when a vehicle or its load are assigned to a new vehicle, perhaps with a new driver – can leave ice cream standing in a non-refrigerated area for far too long.

Arriving at a distribution centre, goods are offloaded, introducing swings in temperature that can range from almost imperceptible to completely irresponsible. In hotter regions of the world, some proportion of the goods may be significantly affected, reaching internal temperatures as high as -10°C (14°F) degrees. Once in storage, temperatures are likely to be a stable -20 (-4°F) in highly controlled facilities, but can easily climb to -15°C (5°F) in less controlled ones.

A similar situation may occur when goods leave the center in smaller consignments for retail outlets: some goods will take too long to be loaded, affecting the temperature of externally positioned packages. And again, the truck ride may present similar problems to those of the original factory-to-center trip.

Welcome to the Wild West

Retail outlets are the Wild West of the cold supply chain, where just about anything can happen. For one reason or another, such as overly busy (or overly relaxed) shop floor staff, it can take far too long to get the goods into retail display cabinets. During this time, a temperature that rises to -12°C (5°F) is not unusual. Once in the outlet’s storage cabinet, the temperature drops to -18 and by now, the product can have lost much of its original quality. The worst, however, is yet to come.

Supermarket storage cabinets require periodic defrosting, during which time the goods are removed and often placed next to the cabinets. In some parts of the world, where electricity is considered an expensive overhead, cabinets are turned off at night – or power outages must be expected weekly or even daily. Finally, lids can be left off the cabinets, introducing significant delays and temperature fluctuations if left undiscovered by staff. In all, the challenging journey from factory to retail outlet could threaten any ice cream brand’s success.

Home is where the heat is

Then there’s the consumer. On a sunny day, the interior of a family car can exceed 30°C (86°F). So, in the 20 minutes that typically passes from the moment the ice cream is plucked from the cooling cabinet until it arrives safely in the home freezer, its temperature may rise to -12°C (5°F) or more. Close to, or actually melting as it waits on the table, a perfectly good ice cream can become almost unrecognisable.

Combatting the Heat Shock Effect

Ensuring Heat Shock stability provides a better consumer experience, stronger brand perception, increased re-purchasing and a better bottom line result. To achieve this stability, manufacturers need to take a holistic approach, combining know-how and experience, the right emulsifier system and production process, optimised packaging, and improved control of storage and distribution temperatures. Of course, not all of these factors are within the manufacturer’s control. Here, emulsifier systems once again come to the rescue, equipping the product to better withstand quality challenges.

Emulsifiers commonly used in ice cream include mono-diglycerides (E471), lactic acid esters (E472b), propylene glycol esters (E477) and blends of these. Propylene glycol esters, for example, protect against the Heat Shock Effect by ensuring small ice crystals are created during freezing and reducing their tendency to grow during the journey to the consumer’s table.