What freeze-dried sweets are, and why they crunch

The vacuum does the work, not the ice

A freeze-dryer normally works on water: it freezes the food, then draws the ice off as vapour. Sweets hold very little water, and almost none of it freezes. What changes them is the vacuum. When the air is pumped out of the chamber, the air trapped inside a sweet expands, and if the sweet is soft enough, it puffs up like a balloon.¹

Warmth is what makes it soft enough. Sugar has a point, its glass transition, above which it stops being a rigid glass and turns soft and mobile; cooled and dry, it sets hard again. Dry sucrose crosses that line at 62 °C, glucose at 31 °C and fructose at 5 °C.² So the sweet is warmed until the sugar gives, the vacuum stretches it from the inside, a little water leaves, and the stretched sugar cools into a brittle foam.

How much of this is understood is another matter. A seminar at the University of Wisconsin–Madison’s food science department reported, as a preliminary finding, that such sweets are really “vacuum oven puffed”, and called the reason they expand the biggest open question in a field with “a literature gap”.³

Soft sweets puff, hard ones don’t

If it bends or chews at room temperature, it will probably puff. If it’s hard and glassy, there’s nothing to stretch.

Every bag in the Sweets range started as a soft sweet:

• Sour Keys: sour gummies with a sugared coat.
• Rainbow Crunch: fruit chews, the kind that inflate into round, crisp balls.
• Strawberry Bears: gummy bears, still recognisably bears.
• Peach Rings: peach rings that keep their sugared surface.
• Cola Bottles: cola bottles, a gummy from end to end.
• Marshmallows: marshmallows, which are mostly air before they even go in.

Weight and price of each bag of sweets

Pouch	Net weight	Price
Sour Keys	50 g	€4.95€99.00/kg
Rainbow Crunch	50 g	€4.95€99.00/kg
Strawberry Bears	50 g	€4.95€99.00/kg
Peach Rings	50 g	€4.95€99.00/kg

Weight and price of each bag of sweets

• Sour Keys

  Net weight

  50 g

  Price

  €4.95€99.00/kg

• Rainbow Crunch

  Net weight

  50 g

  Price

  €4.95€99.00/kg

• Strawberry Bears

  Net weight

  50 g

  Price

  €4.95€99.00/kg

• Peach Rings

  Net weight

  50 g

  Price

  €4.95€99.00/kg

Cola Bottles come in a bag of 50 g at €4.95 (€99.00/kg); the marshmallows, being mostly air, in a bag of 30 g at €4.95 (€165.00/kg).

The sugar stays where it was

Nothing leaves but a little water, so every gram of sugar that went in is still there. Per 100 g the figures stay the same or rise slightly, because the water that left weighed something. A puffed sweet is bigger and weighs almost what it did, so read the sugar on the bag as you would for any other.

Dry, from the bag

There’s no preparation. Open the bag and eat them as they are; water would undo the crunch. The one exception is a few marshmallows dropped on a hot chocolate just before you drink it, where they crunch for a moment and then melt.

For a party, tip a handful into a dry bowl and put the bag away again. Out of the bag, they start taking in damp from the air straight away, and a bowl left out on a humid evening goes soft before the cake is cut.

Keeping the crunch

Sugar draws water from the air, and water is what turns a glass soft again: the foam that was crisp goes chewy, then sticky.² Every time a bag of dried food is opened, the air and moisture that get in take a little more of its quality,⁴ and humid weather speeds it up.⁵ On the coast in August, close the zip after every handful; the end of the film is too late.

Fruit keeps crisp the same way once its water has gone, which is half the story of freeze-dried fruit. In a cooked dish the water does leave as ice, and that process is set out in the difference between freeze-dried and dehydrated.

A taste of three, or one of every bag

The Sweets Discovery Pack is Sour Keys, Rainbow Crunch and Strawberry Bears for €12.90, one bag each: a gummy, a chew and a bear, to find out which texture you like. The Sweets Sharing Pack holds one of every bag for €24.90: a bowl of each on the table and nobody arguing over the bears.

From our range

Sweets Discovery Pack

Three textures side by side, to find the one you’ll come back for.

€12.90Hear from us before the shop opensSee the three bags