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Holding off Heat Shock with emulsifiers and stabilizers
Ice cream manufacturers care deeply about the quality of their products – whether their market is a premium one or more mainstream. And they put every effort into ensuring that the ice cream leaving their production plants consistently makes the grade. What the consumer ends up experiencing, however, is likely to be something quite, quite different – and it’s due to a phenomenon called ‘Heat Shock’.
Ups and downs
In a nutshell, Heat Shock is a quality-damaging reaction to fluctuations in temperature along the journey from production to the point of consumption. And there are plenty of opportunities for such ups and downs, too: Process errors, extended waiting time on the loading dock, poor refrigeration during transport, retail level entry and placement in storage cabinets, power outages and power-saving tactics at retail outlets, the long, unrefrigerated journey to consumer freezers and, finally, removal and re-storage in home freezers until the container is empty.
Heat-shocked ice cream, when it’s worst, becomes a crunchy, gritty, watery disappointment instead of a smooth, full-tasting indulgence. That’s because, with each rise and fall in temperature, a little water is released, migrating to nearby small crystals and expanding their size until they become unavoidably (and unenjoyably) noticeable to the consumer.
With so many uncontrolled and uncontrollable dangers along the way, it may seem as though little can be done to maintain ice cream’s quality. In fact, however, there are some quite effective things manufacturers can do to guard against Heat Shock and keep their ice cream’s quality as high as possible.
Let’s start with the recipe itself. Here, we can single out three ingredients that can make quite a difference to the product’s Heat Shock resistance:
- Milk solids
- Additives in the form of emulsifiers and stabilizers
Clearly, the temperature at which the ice cream’s all-important, foamy network structure solidifies or begins to dissolve (its freezing point) will determine how often and how much free water will be released.
The first two on our list above, milk solids and sugars, can help us to adjust the product’s freezing point. Getting the types of these ingredients just right, as well as the amounts used, is crucial.
Milk solid choices
Let’s think about milk solids for a moment. The first thing to note is that they’re a relatively expensive ingredient. So, while using plenty of high-quality milk solids typically brings a more indulgent, more reliable eating experience, that’s not a strategy that will suit every manufacturer’s or consumer’s budget. Reducing the amount of milk solids in an ice cream product, however, means you necessarily have a higher water content – and that means greater potential for ice crystal expansion whenever the temperature varies. Here’s the basic rule of thumb: If you’re not going to use much, then make sure you choose high-quality milk solids – and make sure, too, that it it’s in an optimal form (powder, milk or cream) for creating the texture you want.
Sugars influence ice cream’s freezing point and its taste. And, if there’s one thing to remember about their relation to ice cream’s freezing point, it’s this: small changes in composition or amount are likely to have a big effect.
But it’s not a simple matter of decreasing the amount of sugar, for example, to combat Heat Shock. You may, for example, need to add more sugar to achieve the softness you’re looking for in a free-flowing application. But by doing so, you’ll lower the product’s freezing point, opening it up to increased damage on its journey to the consumer.
As mentioned above, it’s not just the amount of sugar that matters. It’s also its composition. Most manufacturers use a blend of refined sugar and syrup, even adding a small amount of salt (which any high school chemistry student could tell you makes it harder for liquids to freeze). As you can see, therefore, adjusting the product’s sugar types and amounts isn’t a task for the inexperienced!
Making it easier
Is there an easy answer to the problem of Heat Shock? To some degree, at least, there is. That’s because the right blend of emulsifiers and stabilizers can do far more than many people realise!
The most common emulsifiers used in ice cream are mono-diglycerides (E471), lactic acid esters (E472b), propylene glycol esters (E477) and blends of these. These powerful yet safe additives position themselves in the interfacial layer between the fat/protein and water, helping to improve or control a wide range of phenomena from fat emulsification to melting resistance, mouth-feel and, yes, Heat Shock stability.
Different emulsifiers, however, will have quite different effects. Adding propylene glycol esters such as propylene glycol monostearate (PGMS), for example, protects against the Heat Shock Effect by ensuring small ice crystals are created during freezing and reducing their tendency to grow. Another popular choice, monodiglyceride (E471), comes in many forms and qualities (differing in fatty acid composition, and in the levels of mono and diglycerides) each bringing out different qualities in the final product.
Of course, it takes a bit of work and a lot of expertise to find the right combination and quality of emulsifiers and stabilizers. For example, not all emulsifiers work well with milk replacers (cheaper milk solids used to replace skim milk powders) So, in this case, more trial and error is involved in figuring out exactly which additives, combinations of additives and dosages will work best.
Is that all?
Once you’ve equipped your recipe with the right amount and composition of milk solids and sugars, and you’ve enlisted the quality-protecting power of emulsifiers and stabilizers, you should be ready to face Heat Shock and win, right? Almost. There are still many points to consider in your mixing, aging and freezing processes. Even packaging choices are likely to make a difference! For a more in-depth look at overcoming the effects of Heat Shock, you might like to read this article, where I dig into the details and show the results of specific trials.