Ice Cream: production process and maths
Once consumed only during the warm months, ice cream now plays an important role in our diet throughout the year.
For lay people who ignore baking or ice cream production, it is a sort of simple dessert made of milk, sugar, eggs or fruit purees all mixed together and frozen.
In actual fact making ice cream does require a considerable knowledge of the physical transformations of ingredients and their processing techniques.
We could talk about ice cream for a month, but I’ll try to keep it short and summarise in this post the most important things you need to know.
Balancing ice cream ingredients
Ice cream is made of liquid and solid ingredients plus air.
To obtain the desired ice cream we need to know the correct ratios of ingredients and how to combine them.
Sugars lower the freezing point of liquids, hence they are the anti freeze of ice cream.
These are the percentages of sugars you need:
- 16-22% in cream ice creams
- 26-30% in fruit ice creams
When our ice cream is too soft, it tends to collapse and looks very shiny, the balancing mistake lies in an excess of sugars.
Conversely, if the ice cream is too hard, almost rocky and unscoopable this can be caused by insufficient sugar content.
The problem, though, is that adding too much sugar to our dessert can make it nauseating:
this is the reason why sugars like dextrose are used: they have an anti-freezing power similar to sucrose but a lower sweetening power.
Sugars possess an anti-freezing power and a sweetening power that allow us to act on structural parameters.
Sucrose is taken as a standard of 1 to establish sweetening power.
A quick glance is enough to realize that sweetness varies among different types of sugar:
- Fructose 1.1-1.7
- Dextrose 42 DE 0.7
- Glucose 0.5- 0.6
- Maltodextrins 0.1- 0.2
- Inverted sugar 1.2
- Lactose 0.2 – 0.6
- Isomalt 0.5
- Sorbitol 0.6
- Maltitol 0.8
- Honey 1.3 – 1.5
- Aspartame 200 times sweeter than sucrose
- Stevia 300 times sweeter than sucrose
- Sucralose 650 times sweeter than sucrose
Table sugar – or sucrose – is taken as a standard of 1 for antifreezing power, too:
- Fructose 1.9
- Dextrose 1.8
- Glucose 0.9
- Maltodextrins 0.3
- Inverted sugar 1.9
- Lactose 1
- Honey 1.9
If you pasteurize the whole lot and separate flavours later on, remember to consider the sugar content of flavouring pastes:
zuppa inglese (similar to trifle), crème caramel, cassata, etc., tend to make ice cream too soft, therefore you’ll have to add a small amount of milk to perfectly rebalance its structure.
Fats give structure and quality to ice cream thanks to a property that makes them solid with the cold.
They are contained in milk, cream, butter, egg yolk
(and yet I have seen people adding palm oil to the mixture to cut costs!!!)
The ideal fat percentage is between 6 and 12%.
Again, if you pasteurize the whole batch and add flavours later on, remember to calculate the fats contained in flavouring pastes.
The structure of ice cream with added hazelnut, pistachio, peanut, almond paste or similar flavouring pastes is too thick, so you’ll need to add some dextrose to make the ice cream perfectly scoopable again.
Non-fat Milk Solids
Non-fat milk solids refer to what is left after all the water and fats are removed from liquid milk.
They consist of proteins, lactose and mineral salts. They are quite important because they help give consistency to the ice cream by reducing the amount of frozen water in the finished product and keeping in the air during
the whipping phase.
Their percentage must remain between 7 and 12%.
Stabilizers – Emulsifiers – Thickeners (more solid ingredients)
Stabilizers are hydrophilic colloids, i.e. they are attracted toward water and bind it, bringing more consistency to the mixture; they also prevent it from melting too quickly and dripping into the ice cream.
Such troubles do not arise when equipment such as Pacojet is used to make plated ice cream desserts, because the ice cream is consumed shortly after production.
The most common are carob seed flour, guar gum, alginate flour, carrageenan, agar-agar and pectin.
Their percentage varies from 0.5 to 5%, but heed manufacturers’ directions to avoid ending up with “gluey and spongy” ice cream.
Stages and Equipment of Ice Cream Production
During this stage liquids, sugars, fats, non-fat milk solids and stabilizers are mixed together in the pasteurizer.
Mixing is carried out according to specific parameters so that solids are well blended into liquid ingredients.
Liquids must be added at cold temperatures; when the mixture reaches 40°C powder ingredients are added.
Cream can be added during the heating phase to give more structure, or during the cooling phase to make taste more intense.
As we know, pasteurization is the process used to eliminate most pathogens, i.e. disease-carrying microbes, from foods.
There are 3 kinds of pasteurization:
- Low pasteurization – 65°C for 25-30 minutes, quick refrigeration at 1-4°C.
- Mid pasteurization – 72°C for 12-15 minutes, quick refrigeration at 1-4°C.
- High pasteurization – 82/85°C for 10-15 seconds, quick refrigeration at 1-4°C.
At this point the mix is “aged”, i.e. set aside for 12 hours so that milk proteins are well hydrated and fat particles crystallize; this also improves the later addition of air.
This process involves freezing the mix in a batch freezer or churner; during this stage ice cream undergoes two crucial moments: freezing the mix and incorporating air.
The addition of air is called “overrun” and increases the volume of the ice cream mixture, making it “semi-whipped”.
On that account air is a crucial “ingredient”: without it, ice cream would be heavy, cold to the palate and not very creamy.
Ideally artisanal ice cream has an overrun between (at least) 20% and 45% (industrial ice creams have much higher overrun).
For years now ice cream machines (like Trittico), have been available on the market to pasteurize and cream very quickly.
At the point of discharge from the churner, ice cream has a temperature of about -6/-8°C, therefore if it is not frozen it tends to collapse.
It takes about ten minutes in a blast chiller to stabilize the ice cream in the pan creating a sort of iced crust that protects both the ice cream and its overrun (incorporated air).
At this point the ice cream is ready for display. Ice cream parlours usually store ice cream at -13/-16°C to preserve scoopability without affecting consistency.
This is the reason why artisanal ice cream becomes as hard as an ice cube in our home freezer: it is made to be stored in ice cream parlour display counters, not in -18°C freezers.
Companies that produce ice cream for domestic consumption, on the other hand, balance it in such a way that it is soft and scoopable at -18°C.
Have a nice ice cream dessert!