The Magic of Melting Ice Cream: Why different ice creams melt at different rates?
Ice cream is one of the most
popular, loved frozen treats. It is easily available and affordable. I have
never met anyone who has never tasted ice cream. But have you bought different brands
and types of ice creams and kept it at room temperature just to observe how much time it takes for them to melt. If you have done this, you would have noticed that
not all of them melt at the same speed. Some will completely melt within a few
minutes while others may take longer.
So what makes ice cream melt and why not all of them melt within the same time? Here's what you need to know.
Ice cream is usually made by mixing
the milk fat, sugar (or sweetener), stabilizer and emulsifier. This mix is then
pasteurized, homogenized, aged and frozen. During this whole process, water and
fat molecules in the mix are brought together with the help of protein molecules,
ice-crystals are formed, and air molecules get incorporated. In the end,
ice-cream is a frozen foam that consists of air dispersed in the ingredient
mix.
When you take out the ice-cream from the fridge and place it in the ambient or warm temperatures, within a few minutes you’ll find milky fluid replacing the solid structure of ice-cream a.k.a the magical phenomenon of melting. But Why? When you place the ice-cream open in the air, the air molecules, which are at a higher temperature, travel towards the surface of the ice-cream and transfer their heat to the surface of the product. As the ice-crystals on the exterior absorb the heat from the surroundings, they start to melt into the water while the temperature of the surrounding begins to cool down (as they have lost their heat to the ice-cream). Once melted ice-crystals turns into water, the water begins to flow all over the surface of the ice-cream. The heat from these flowing water molecules reaches the interior of the ice-cream and as a result, the ice-cream begins to melt from the insides too.
It is important to note that not all ice-creams melt at the same speed or in the same way. There are a lot of factors that influence the way and the rate at which a scoop of ice-cream melts. Some of these factors are heat transfer rate (that is determined by external temperature, overrun, size of air bubbles), number and size of the fat globule clusters and nature of ice-crystals.
Overrun
During the freezing, the air is incorporated into the ingredient mix. This incorporation of air molecules into the ice-cream increases the volume of the final product. Overrun is defined as the volume of ice-cream obtained in addition to the volume of the mix. The amount of volume increased by the air molecules affects the melting rate of the ice-cream. Usually ice-creams with low overrun melt rapidly while the ice-creams with high overrun melt slowly.
The
network of fat molecules
A lot of you might already know that water and oil don’t mix well and if put in the same container, these two tend to separate. Ice-cream is an emulsion of water and oil. In the manufacturing process, after the homogenization, the big fat droplets in the mix are broken down into smaller droplets. When this happens, the protein molecules attach themselves on the surface of these smaller fat particles. These chains of proteins form a membrane around the fat particles and it, in turn, leads to a more stable emulsion. But during the freezing, these membrane-coated fat molecules try to reach each other and end up forming a complex network of fat globules. If the developed fat network is very extensive, it’ll melt slowly. But if the network is poorly developed, the ice-cream melt very rapidly.
Ice-Crystals
The bigger the size of ice crystals, the more easily the ice-cream will melt. If the ice-crystals are smaller in size and more in number, they obstruct the path of heat transfer and it takes longer for the insides of the ice-cream to absorb heat. This slows down the melting of the ice-cream.
Total Solids
Ice cream is a network of 3 components- air, liquid and solids. The term 'total solids' in an ice-cream is defined as the sum of all dry and solid ingredients. These ingredients include fat, sugar, MSNF (milk-solids-not-fat- i.e. lactose, milk proteins and minerals), stabilizers and emulsifiers. The total solids in an ice cream mix affect the melting rate of the end product. It has been found that ice creams with higher amount of total solids melted faster than the ice-creams with a lesser amount of total solids.
Type of Sugar Used
Different companies use different types of sugar (liquid and solid) in ice cream and the kind of sugar used influences the melting rate of the ice cream. Few sugars lead to high melting rate, while others slow down the melting of the ice cream.
Viscosity
Viscosity is defined as the
resistance of fluid foods to flow. If a liquid is less viscous, it means
that it'll will flow easily, for e.g water. Fluid foods with higher viscosity will
resist flowing, for e.g tomato ketchup. It has been reported in a few studies that a
thicker, more viscous mix will lead to low melting rates.
thanks!
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