Science and safety
Why ice cream freezes the way it does: fat, sugars, air and ice crystals. And how to make ice cream safely at home.
Ice cream science
How zmrzka calculates the composition of the mix
Fat, milk solids, sugars, total solids, PAC, POD and Brix: where the numbers on every recipe come from, which databases the ingredients are taken from and where the calculation reaches its limits.
PAC and POD: why ice cream is soft and how sweet it tastes
The anti-freezing power and sweetness of sugars compared with sucrose. How to soften ice cream with dextrose, invert sugar, alcohol or salt, and where the limits are.
What fat, sugar, protein and air do in ice cream
Ice cream is a foam and an emulsion at the same time. The roles of fat, milk solids, sugars, stabilisers, emulsifiers and air, and what happens when there is too much of something.
Ice crystals: why homemade ice cream goes hard and grainy
Crystal size decides how smooth ice cream is. Why freezing speed matters, what recrystallisation is and how to keep homemade ice cream smooth even after several days.
Pasteurising and ageing the mix: temperatures, times and why to wait
To what temperature and for how long to heat the mix, where the threshold for eggs lies and why it pays to leave the mix in the fridge overnight.
Stabilisers at home: locust bean gum, guar, pectin, starch and gelatine
A small amount of stabiliser slows crystal growth and improves the body of ice cream. Which doses are quoted, how to activate them and where the numbers are unverified.
Overrun: how much air is in ice cream
Overrun tells you how much the ice cream has grown in volume compared with the mix. How it is calculated, why gelato has less air than industrial ice cream and what a home machine can manage.
Safety
Using eggs safely in homemade ice cream
Why raw yolks don’t belong in ice cream, why 71 °C is enough for safety while 82 °C is the cook’s upper limit for custard, and when to reach for pasteurised eggs.
Storing ice cream and what to do when it melts
What temperature to store ice cream at, how long homemade and shop-bought ice cream keeps, and why melted ice cream shouldn’t be refrozen.
Keeping your ice cream maker and kitchen clean
Once the mix has been cooked, hygiene is your only protection against bacteria. How to clean the ice cream maker, the bowl and your utensils, and why leftovers should never go back in.
Listeria and ice cream: who should be careful
Listeria survives freezing, and a small dose is enough to make vulnerable people ill. What outbreaks in the US and the UK showed, and who should take more care with ice cream.
Liquid nitrogen ice cream: why not at home
Nitrogen ice cream looks spectacular, but liquid nitrogen belongs in the hands of professionals. What the risks are and what to watch out for when you buy it.