The two most common IQF freezing belts are the spiral and the straight type. Both freeze individual pieces; they differ in how the belt path is arranged — and that is what decides which one suits a given plant.
The basic difference
Straight IQF runs the belt straight through the freezing chamber. The path is short, so to achieve the required freezing time the belt has to run slowly or the chamber has to be long.
Spiral IQF coils the belt into several tiers within one block. The path is far longer on the same floor area, allowing a longer freezing time without extending the building.
The floor space question
This is the factor that most often decides it. Spiral IQF saves a considerable amount of floor area but needs enough ceiling height to fit the spiral block. Straight IQF takes up a long run of floor but does not demand a high ceiling.
In an existing building, these two constraints usually settle the choice on their own. For a new build, it needs considering at the building design stage rather than being left until the equipment is selected.
The cleaning and maintenance question
This is the point most often underrated in a comparison. Straight IQF has a simple structure, with easy access to every position for cleaning and maintenance. Spiral IQF has multiple tiers, so cleaning is more complicated and takes longer.
For a plant that must clean at the end of every shift under food safety requirements, cleaning time is not a minor detail — it eats into the production time available each day.
The throughput and product range question
- Spiral IQF suits high throughput with relatively uniform product running continuously — where its advantages in floor area and freezing time come into their own
- Straight IQF suits moderate throughput, thin products needing a short freezing time, or plants that change product type frequently
For thin products such as fish fillets, the freezing time is short, so straight IQF is sufficient. For thicker products needing longer, spiral IQF achieves that without an excessively long chamber.
Comparison table
| Criteria | Straight IQF | Spiral IQF |
| Floor area | Takes up a long run | Saves considerably |
| Ceiling height | Low requirement | Needs a high ceiling |
| Freezing Retention Time | Shorter, suits thin products | Longer, suits thicker products |
| Cleaning and maintenance | Simple, easy access | More complex, takes longer |
| Changing product type | More flexible | Less flexible |
| Capital cost | Usually lower | Usually higher |
| Best suited to | Moderate throughput, thin products | High throughput, continuous running |
Five questions before choosing
- How much floor area and ceiling height are available? In an existing building, this constraint usually settles the choice on its own.
- Is the product thick or thin? It determines the freezing time required, and from that the length of belt path needed.
- Do you change product type often? A plant running several product lines needs more flexible equipment.
- What are the cleaning requirements each shift? Cleaning time comes directly out of the production time available.
- What is the target throughput and the expansion plan? Investing for today's throughput, or for the scale you expect in 3 years.
A note on comparing throughput figures
The throughput figure a supplier publishes always relates to a specific product, at a specific thickness and inlet temperature. On the same machine, the actual throughput with a different product can differ substantially.
When comparing, ask for the figure for your own product and your own conditions, not the nominal figure from the catalogue.
Tan Long designs and installs IQF freezing belts to the throughput, product type and site conditions of each individual plant.
If you need to revisit the principles before comparing the two belt types, see what IQF freezing technology is.
Frequently asked questions about choosing spiral or straight IQF
How do spiral and straight IQF differ?
In how the belt path is arranged. Straight IQF runs straight through the chamber, giving a short path. Spiral IQF coils through several tiers, giving a far longer path on the same floor area and allowing a longer freezing time.
Which factor usually decides the choice?
The available floor area and ceiling height. Spiral IQF saves floor space but needs a high ceiling; straight IQF takes up a long run of floor but does not demand height. In an existing building, this constraint usually settles it.
Which type is easier to clean?
Straight IQF, thanks to its simple structure and easy access to every position. Spiral IQF has multiple tiers, so cleaning is more complicated and slower — worth noting for a plant that must clean at the end of every shift.
Which type suits thin products?
Thin products such as fish fillets have a short freezing time, so straight IQF is usually sufficient. Thicker products need longer, and spiral IQF achieves that without an excessively long chamber.
Should you trust the throughput figure in the catalogue?
Not directly. The published figure always relates to one product at a specific thickness and inlet temperature. Ask for the throughput for your own product and your own conditions.
What should a plant running several product lines choose?
Straight IQF is more flexible when product types change frequently. Spiral IQF comes into its own at high throughput with relatively uniform product running continuously.
Related pages
- Mesh belt IQF freezer
- Flat plate IQF freezer
- What is IQF? Principles and applications
- Quick freezing: why it determines quality
- Cold storage solutions for seafood
Engineer Nguyen Toan Thinh (Technical Director)
With over 18 years of practical experience in directing, consulting, designing, and constructing heavy industrial refrigeration systems, ASRS automated warehouses, and IQF freezing systems across more than 29 major national projects.
