Quick Freezing: IQF, Tunnel, and Spiral Freezers
Why Quick Freeze?
Toss freshly wrapped dumplings straight into a freezer, or freeze them with quick-freezing equipment, and the difference when cooked is obvious: slowly frozen dumplings have wrappers that crack and burst when boiled, and fillings that release water and turn dry and stringy.
The reason is ice crystals. Taiwan's Food and Drug Administration (TFDA) explains that in typical foods, about 80% of the water freezes between -1°C and -5°C; this temperature range is called the "zone of maximum ice crystal formation," and the longer the food stays there, the larger the ice crystals. Large ice crystals pierce cell and gluten structures, so water is lost on thawing and texture suffers. The TFDA also explains that quick freezing uses specialized equipment to freeze food rapidly within about 30 minutes, so it passes through this range in a short time and forms small ice crystals.
For dumplings and buns, quick freezing has another benefit: the surface freezes hard quickly, so pieces stay separate without sticking, and they don't clump together during packaging.
On the regulatory side, Article 9 of the Standards for Food Factory Construction and Equipment (食品工廠建築及設備設廠標準) requires frozen food factories to have production equipment for freezing; Annex 1 of the Regulations on Good Hygiene Practice for Food (食品良好衛生規範準則) requires frozen storage equipment to be kept at -18°C or below. Quick-freezing equipment "gets it frozen," while the freezer "keeps it frozen"; the two serve different functions.
What Is IQF?
IQF stands for Individually Quick Frozen, meaning each piece of product is frozen separately and quickly rather than frozen together as a whole tray or block. Small products such as dumplings, tangyuan, sweet potato balls, and taro balls are mostly meant to be IQF, so consumers can take out a few at a time to cook.
To achieve IQF, products must be kept apart during freezing, with strong cold air or refrigerant removing heat evenly. Tunnel, spiral, and fluidized-bed freezers can all do it; the difference lies in suitable product shapes and volumes.
How Do Tunnel and Spiral Freezers Differ?
Tunnel freezer: Products sit on a straight conveyor belt and pass through a tunnel filled with cold air, going in one end and coming out frozen at the other.
- Advantages: Simple structure, easy loading and unloading, and suitable for flat or easily deformed products or products that shouldn't go around curves.
- Drawbacks: Enough dwell time requires a long enough tunnel, which takes up a lot of floor space.
Spiral freezer: The conveyor belt winds round and round upward (or downward) inside the freezing chamber like a spiral staircase, and products travel a very long path along the spiral.
- Advantages: The long path is packed into a vertical space, so it uses relatively little floor area and suits high-volume continuous production.
- Drawbacks: The equipment is tall, so the factory needs sufficient ceiling height, and initial investment is usually higher.
Other types: Cabinet (batch) blast freezers suit the start-up stage; fluidized-bed freezers use upward-blowing cold air to "float" small products apart while freezing, suiting small products that stick easily; cryogenic freezers using liquid nitrogen and the like freeze quickly, but the refrigerant is continuously consumed.
How to Choose Freezing Equipment
- Output: How many kilograms per hour need freezing determines the equipment size.
- Product shape and weight: Buns are large and need longer freezing times; dumplings are flat and deform easily, so pay attention to the belt surface and placement.
- Infeed temperature: If steamed buns go into the freezer without being cooled first, the heat load rises sharply and freezing takes longer.
- Outfeed requirements: What core temperature the product must reach at the exit, which can be spot-checked with a probe thermometer.
- Factory conditions: length, height, power, and where the condensing unit goes.
- Cleanability: whether the belt, evaporator, and drainage are easy to clean and defrost.
A freezer's capacity varies with product, infeed temperature, and environment, so when comparing equipment, ask suppliers for an assessment based on your own product conditions rather than just looking at catalog figures.
FAQ
Q: Can I use a household freezer to freeze dumplings for sale?
A: Household freezers freeze slowly, forming large ice crystals and poor quality; under the factory standards, frozen food factories must have production equipment for freezing.
Q: What does IQF mean?
A: Individually quick frozen: each piece is frozen separately and quickly, so they don't stick together in a block.
Q: At what temperature should products be stored after quick freezing?
A: Under Annex 1 of the Regulations on Good Hygiene Practice for Food, frozen storage equipment must be kept at -18°C or below. For details, see Freezers, Cold Rooms, and Temperature Records.
Q: Which is better, spiral or tunnel?
A: Neither is better in absolute terms. If you have enough factory length and the product shouldn't go around curves, choose tunnel; if floor space is limited, volume is high, and you have the ceiling height, choose spiral.