The short answer
Diet, zero and “no added sugar” drinks won’t make proper slush in a home slush machine on their own. Ninja says:
“Sugar-free or low-sugar liquids won’t slush because they need at least 4% sugar for the right texture.”
Tower likewise says its Slushie Fusion is not for diet or zero/low-sugar drinks and recommends a minimum of 5% sugar. The science is in how slush machines work.
Alternatives Ninja lists
Ninja suggests coconut sugar, maple syrup, agave syrup, simple (sugar) syrup and honey. These are all still sugars — the NHS counts honey and syrups as free sugars. Ninja also mentions allulose, which it says “can help slush but may make it sweeter”.
If your drink is too low in sugar, Ninja’s fix is to add 15–30 ml of syrup, juice, sugar or honey per serving, mixed in before pouring.
Why not glycerol?
Commercial slush often uses glycerol (E422) to keep a slushy texture with less sugar. The Food Standards Agency advises that children under seven should not have slush drinks containing glycerol, and that applies to home kits with glycerol concentrates too. It is not a fix we recommend for family slush. See the safety guide.
Ways to cut the sugar per cup
You can’t go much below the 4% line, but you can control how much anyone drinks:
- Serve smaller cups. At 4% sugar a 260 ml cup holds about 10 g of sugar; a 150 ml cup about 6 g.
- Aim for the minimum, not double it. Many drinks are well above 4%; diluting a sweet squash a little further (and checking it with the calculator) keeps it slushing with less sugar per sip.
- Serve water alongside, especially for children.
The bottom line
Slush is a sweet treat by design. If you need a genuinely sugar-free cold drink, a blended ice drink or plain ice water is a better fit than a slush machine.