What are ice cream stabilizers?

Stabilizers are hydrocolloids that are water-soluble, i.e. they disperse in water, and are commonly used in ice cream making. Stabilizers extensively used in the ice cream industry include guar gum, locust bean gum, carboxy, ethyl cellulose (CMC), sodium and propyleneglycol alginates, xanthan, gelatin, and carrageenan (Goff and Hartel, 2013). These stabilizers are derived from plants, bacteria, and animal by-products. Although derived from natural sources, stabilizers are considered food additives under European law.

Plants

Most stabilizers used in ice cream making are of plant origin. These include sodium alginate (E401) extracted from brown seaweeds, carrageenans (E407) extracted from red seaweeds, locust bean gum (E410) and guar gum (E412) extracted from tree seeds, pectin (E440) extracted from citrus peel and apple pomace, carboxymethyl cellulose (CMC) (E466) extracted from cotton and wood pulp, and sodium (E401) and propylene glycol (E477) alginates extracted from kelp.

Bacteria

Xanthan (E415), a bacterial polysacharide produced by the bacterium Xanthomonas campestris, is used as a stabilizer in ice cream making.

Animal by-products

Gelatin (E441), a polypeptide of animal origin (mostly from bones, bovine hides, and pig skin) is also used as a stabilizer. Gelatin was traditionally used as a stabilizer in ice cream making but has now largely been replaced by polysaccharide hydrocolloids in ice cream making. So we know that stabilizers are food additives that are derived from plants, bacteria, and animal by-products.  Let’s turn now to why stabilizers are used in ice cream making.

Why are stabilizers added to ice cream?

So just why are stabilizers added to ice cream? According to Goff and Hartel (2013), the primary purposes for using stabilizers in ice cream are to:

• increase mix viscosity;
• retard ice crystal and lactose crystal growth during storage;
• help prevent shrinkage of the ice cream during storage and
• reduce the rate of meltdown.

Let’s look at each of these points individually.

Increase mix viscosity

Mix viscosity can be loosely defined as the thickness of the ice cream mix. Generally speaking, the thicker and more viscous a mix is, the better the texture is likely to be. A certain level of viscosity is also essential for proper whipping and retention of air that is incorporated during the churning process, and for good body and texture in the ice cream (Goff and Hartel, 2013). Increasing the concentration of stabilizer, protein, fat, and total solids in a mix will increase viscosity, with stabilizers having the greatest effect on mix viscosity (Goff and hartel, 2013). Concentrating a mix by evaporating some of the water will also increase mix viscosity. I have found that heating a mix at around 71.4°C for 60 minutes denatures whey proteins, which contributes significantly to smooth and creamy texture, and also increases mix viscosity thus reducing the need for stabilizers.

Retard ice crystal growth during storage

All ice cream will eventually become sandy and coarse as the ice crystals grow during storage. Small ice crystals, essential for smooth and creamy texture and developed during the whipping process, will eventually grow into large crystals that are detectable on the tongue. These crystals can be easily seen when you open an ice cream tub that has been left in the freezer for months and find large bits of ice on your ice cream.

Stabilizers are added to ice cream to slow down the rate at which ice crystals grow during storage. Stabilizers retard ice crystal growth by slowing the rate of diffusion of water to the surfaces of growing crystals (Goff and Hartel, 2013). Although stabilizers keep ice crystals smaller for longer during storage, they actually have little (Caldwell et al., 1992) or no (Sutton and Wilcox, 1998a,b) impact on the ice crystal size distribution in ice cream right after it has been churned in the machine and also little or no impact on initial ice crystal growth during quiescent freezing and hardening (Flores and Goff, 1999a), but they do limit the rate of growth of ice crystals during recrystalisation (Flores and Goff, 1999b).

So, we know that small ice crystals are essential for smooth and creamy texture (see my post on ice crystal size effect on texture). Stabilizers do not have an effect on the size of ice crystals at the time the ice cream is churned in the machine. This means that adding stabilizers will not promote the formation of small ice crystals when the ice cream is made. Ice crystals will grow over time and the bigger they grow, the sandier the texture becomes. The longer ice cream is left in the freezer, the bigger ice crystals grow. Stabilizers are added to retard this ice crystal growth so that the texture stays smoother for longer.

Because stabilizers do not have an effect on ice crystal size when ice cream is made, ice cream that is freshly made and eaten within a short time does not really need added stabilizers. Stabilizers are mainly added to ice cream to increase its shelf life in the supermarket by keeping ice crystals smaller for longer. That is why you rarely find added stabilizers in good ice cream parlours where the ice cream is freshly made, consumed within a short period of time after it has been made, and not stored for long periods of time.

Help prevent shrinkage of the ice cream during storage

Shrinkage can be seen in ice cream that has been stored for long periods of time and has contracted or ‘deflated’ so that it no longer touches the sides or the lid of the container. Shrinkage is sometimes noticeable when you open an ice cream tub that has been left in the freezer for a while and notice that it has deflated and looks somewhat flat. Shrinkage results from a loss of air bubbles as they come together and begin to form continuous channels, eventually leading to collapse of the product itself into the channels (Turan et al., 1999). Stabilizers are added to ice cream to slow down the rate of shrinkage.

Reduce the rate of meltdown

The melting rate of ice cream is of great importance; no one likes an ice cream that quickly turns to slush as you are eating it. Added stabilizers increase the melting resistance of ice cream due to their water-holding and microviscosity enhancement ability (Goff and Hartel, 2013).

Ice Cream defects caused by stabilizers

Although stabilizers have many beneficial functions in ice cream, too much stabilizer can have adverse effects on texture. These include a gummy or sticky texture that is often slow to melt and a heavy or putty-like texture.

Conclusion

Although stabilizers have many beneficial effects on ice cream, I have found that extremely smooth and creamy ice cream can be made at home without the need for added stabilizers. The beneficial effects of added stabilizers can be easily achieved by heating a mix to somewhere around 71.4°C and keeping it there for 60 minutes. This increases mix viscosity and improves the water-holding capacity of protein. The increased milkfat used in home made ice cream also plays a similar role to added stabilizers in that it will retard or reduce the rate at which ice crystals grow during storage, keeping the smooth and creamy texture for longer. I still maintain that these food additives should not be used in ice cream and that the main reason they are added to commercial ice cream is to allow companies to keep their ice cream on supermarket shelves for longer. Because us home-made ice cream enthusiasts devour our home-made ice cream in a matter of days, we don’t need to store it in the freezer for months and months and do not, therefore, need to add stabilizers. I hope that helps. All the best, Ruben.

References:

Bahramparvar, M. and M Tehrani. 2011. Application and functions of stabilizers in ice cream, Food Reviews International, 27:4, 389-407

Caldwell, K. and D. Goff, and D. Stanley, 1992. A low temperature scanning electron microscopy study of ice cream. 1. Techniques and general microstructure. Food Struc. 11:1-9

Clarke, C., The Science of Ice Cream, 2004

Flores, A. and D. Goff 1999a. Ice crystal size distributions in dynamically frozen model solutions and ice cream as affected by stabilizers. J. Dairy Sci. 82:1399-1407.

Flores, A. and D. Goff, 1999b. Recrystallisation in ice cream after constant and cycling temperature storage conditions as affected by stabilizers. J. Dairy Sci. 82:1408-1415

Goff, D. and R. Hartel, Ice Cream, Seventh Edition, 2013

Sutton, R. and J. Wilcox, 1998a. Recrystallisation in model ice cream solutions as affected by stabilizer concentration, J. Food Science. 63:9-11

Sutton, R. and J. Wilcox, 1998b. Recrystallisation in ice cream as affected by stabilizers. J. Food Science. 63:104-197

Turan, S. and R Bee. 1999. Measurement of gas phase morphology in ice cream. In Bubbles in Food, pp. 183-189.