As you run your tongue over perfectly creamy ice cream, the sugars hit the sweet tastebuds and immediately tell your brain that a high-calorie food is on its way. The brain immediately switches to “GIVE ME MOAR” mode. The fats in the ice cream, aerated perfectly between really tiny ice crystals, evenly coat the mouth, further indicating to the brain that nine calories per gram of fat are coming in. And then the complex aromas of vanilla release themselves from the fats and travel to the back of your mouth and float up to your nasal cavity as you breathe out and tell your olfactory receptors and brain that the joyful smells of your childhood have arrived.
Ice cream is, at its basic component level, just four things: milk, cream, sugar and flavouring. It is also an emulsion of fat and water, a foam of air bubbles inside water and is also simultaneously solid (ice), liquid (water) and gas (air bubbles) in an uneasy state of coexistence. Too many things have to go right for ice cream to work.
Let’s start with temperature. If the temperature is not low enough, the ice crystals in ice cream will be too large and spoil its texture and mouthfeel. A large crystal-size is the equivalent of a bed of thorns on your tongue.
The amount of sugar in ice cream is another crucial factor. Sugar has the property of lowering water’s freezing point. As sugary water freezes, ice crystals form, and the remaining water is now more concentrated, depressing its freezing point further. What this does is ensure that the size of ice crystals remains small—this is crucial for a creamy mouthfeel. Too little sugar and you will get ice cream that turns rock hard in the freezer. Too much sugar and it will melt into an unappetising and cloyingly sweet liquid straight out of the freezer.
Great ice cream also uses eggs to improve texture. The fats in the yolk add to the creaminess and also prevent the ice cream from melting unevenly when it comes out of the freezer.
Commercial ice cream also uses a few other ingredients. Starch binders like carrageenan, a seaweed extract, also prevent water molecules from moving around too easily and forming large ice crystals. This is particularly important because home freezers are simply not cold enough and large ice crystals tend to form while your ice cream is sitting around waiting for you to eat it. This is why it’s best to store ice cream either in a separate closed compartment in the freezer or at the back of the freezer, and disable the auto-defrost function in your fridge since temperature fluctuations spoil the texture. Also, transfer store-bought ice creams to flat, shallow, air-tight containers since this ensures the creamy consistency lasts longer. And by the way, Indian “vegetarian” ice creams simply use more sugar, extra starch binders, and skimmed milk powder to replace eggs.
Incidentally, our tastebuds don’t work very well at low temperatures. This is why ice cream is palatable when it’s cold but becomes unbearably sweet as it melts. Vegetarian ice creams are particularly bad offenders.
Kulfi works slightly differently. Here the focus is not on getting ice crystals down to a tiny enough size to make for a perfectly creamy texture. The idea is to flavour the milk with spices, dry fruits, nuts and fruit flavours, cook it down to a thick consistency with heat and then simply freeze it in a mould. There is no slow churning process to ensure small ice crystal size, etc. There is just so much flavour that a gritty mouthfeel is actually preferred as a contrast to an overly creamy texture.
However, to make the greatest-tasting ice cream, you need a rather dangerous ingredient—liquid nitrogen. Simply pouring liquid nitrogen into the milk, cream and sugar mix and churning it will ensure the smallest possible ice crystal size because liquid nitrogen is about 200 degrees Celsius below zero. It goes without saying—do not try this at home.
Krish Ashok is the author of Masala Lab: The Science Of Indian Cooking.
