Why “Frozen Solid” Takes Longer Than You Think: The Complete Science of Freezing for Transport

The 5 Phases of Freezing: Your Complete Journey

When you put a product in the freezer, it doesn’t instantly become “frozen solid.” It goes through five distinct thermodynamic phases. You cannot skip phases, you cannot rush them, and you must complete all five phases before dispatch.

Think of it like baking a cake: you can’t take it out halfway through and call it done just because it looks cooked on top.

PHASE 1: Liquid Cooling Stage ⏱️

What’s happening:
Your product is cooling from its starting temperature down to its freezing point, then slightly below.

The science:
The product is losing heat to the surrounding cold air. The warmer your product starts, the longer this takes. A product at room temperature (20°C) takes much longer than a product already chilled in a fridge (4°C).

Time required:
Depends on starting temperature, volume, and product composition:

• Small item (500g) starting at room temp: 2-4 hours
• Large item (5kg) starting at room temp: 6-10 hours
• Starting from fridge temperature: Cut time by 30-40%

Visual clue:
Product is cold to touch but still completely liquid. No ice crystals visible yet.

What people get wrong:
They think once the product is cold, it’s “almost frozen.” Actually, you haven’t even started the freezing process yet!

PHASE 2: Nucleation Phase ⏱️⏱️

What’s happening:
Ice crystals begin forming throughout the product. This is when the actual freezing starts.

The science:
Water molecules are arranging themselves into ice crystal structures. This phase is very sensitive to impurities in your product – salt, sugar, proteins, and fats all affect how quickly crystals form. The more “stuff” in your product (like a thick stew vs pure water), the longer this takes.

Time required:
Typically longer than Phase 1:

• Simple products (water-based): 3-6 hours
• Complex products (stews, sauces): 8-12 hours
• High fat/sugar content: Even longer (these lower the freezing point)

Visual clue:
Product looks slushy or has ice forming. Edges might be solid but center is still liquid. If you squeeze it, liquid oozes out.

What people get wrong:
They see ice forming and think “it’s frozen!” This is only the beginning. The product is maybe 30-40% frozen at this point.

PHASE 3: Recalescence Phase ⏱️

What’s happening:
Rapid crystal growth! The crystals that formed in Phase 2 now grow quickly throughout the product.

The science:
Once nucleation is complete, crystal growth accelerates dramatically. This is the “rapid freeze” phase. The good news: this is relatively quick compared to other phases.

Time required:
Compared to other phases, this is fast:

• Most products: 1-3 hours

Visual clue:
Product looks solid throughout, but if you checked the internal temperature with a probe, the center might still be above the final frozen temperature.

What people get wrong:
This is where the big mistake happens! The product feels frozen solid on the outside, looks frozen, and seems done. But it’s not – it’s only about 70% of the way there. This is where most people stop and think they’re finished.

PHASE 4: Freezing Phase ⏱️⏱️⏱️

What’s happening:
The crystals continue growing until ALL the water in the product is completely frozen solid.

The science:
The rate of crystal growth is now limited by how fast heat can transfer from the center of the product to the cold air around it. Large products or well-insulated products take much longer here.

Time required:
This is often the longest phase:

• Small items: 4-8 hours
• Medium items (2-3kg): 10-16 hours
• Large items (5kg+): 20-30 hours
• Palletized or packaged items: Add 50-100% more time!

Visual clue:
Product looks and feels completely solid, but the internal temperature might still be higher than it should be. A temperature probe would show the center is warmer than the outside.

What people get wrong:
They think because it’s solid, it’s done. But being solid isn’t the same as being at the proper storage temperature throughout. The center of your product might be at -2°C while the outside is at -15°C.

PHASE 5: Solid Cooling Phase (Tempering) ⏱️⏱️⏱️⭐

What’s happening:
The now-solid product continues cooling down to the actual storage temperature throughout – from surface to center.

The science:
Heat continues transferring from the (warmer) center to the (colder) outside. The product is solid but needs to reach equilibrium – the same temperature all the way through.

Time required:
Often takes as long as all previous phases combined!

• Small items: 6-12 hours
• Medium items: 12-24 hours
• Large items: 24-48 hours
• Palletized goods: 48-72+ hours!

Visual clue:
No visible difference from Phase 4. The only way to know you’ve reached this phase is with a calibrated temperature probe inserted into the center of the product.

What people get wrong:

Almost everyone skips this phase. They think once it’s solid (end of Phase 4), they’re done. This is the #1 reason goods arrive thawed during transport.

⚠️ THIS IS THE CRITICAL POINT

Your goods MUST reach the end of Phase 5 before dispatch.

If you dispatch goods that have only completed Phase 4 (solid but not tempered):

• The center is still warmer than the outside
• During transport, heat from the center migrates outward
• This internal heat, combined with any brief temperature exposure during loading/unloading, causes partial thawing
• Even in a perfectly maintained -12°C truck, your goods will thaw from the inside out

It’s not the courier’s fault – the goods weren’t ready for transport.

Real-World Examples: How Long Does It Actually Take?

Let’s get specific with timelines for common products, starting from room temperature (20°C) in a proper -18°C freezer with good air circulation:

Small Individual Items (500g containers)

Cottage pies, lasagnas, single meal portions:

• Phase 1 (Cooling): 2-3 hours
• Phase 2 (Nucleation): 3-5 hours
• Phase 3 (Recalescence): 1-2 hours
• Phase 4 (Freezing): 4-6 hours
• Phase 5 (Tempering): 8-12 hours

TOTAL: 18-28 hours (call it 24 hours minimum)

Most people freeze these for 6-8 hours and think they’re done. They’re only halfway through Phase 4.

Medium Containers (2-3kg tubs)

Family-size stews, curries, soups in large containers:

• Phase 1 (Cooling): 4-6 hours
• Phase 2 (Nucleation): 8-12 hours
• Phase 3 (Recalescence): 2-3 hours
• Phase 4 (Freezing): 12-18 hours
• Phase 5 (Tempering): 18-30 hours

TOTAL: 44-69 hours (minimum 48 hours, or 2 full days)

Most people freeze these for 12-24 hours. They’re only at the beginning of Phase 4.

Large Bulk Items (5kg+ containers)

Bulk catering portions, large casseroles:

• Phase 1 (Cooling): 6-10 hours
• Phase 2 (Nucleation): 10-14 hours
• Phase 3 (Recalescence): 2-4 hours
• Phase 4 (Freezing): 20-30 hours
• Phase 5 (Tempering): 30-48 hours

TOTAL: 68-106 hours (minimum 72 hours, or 3 full days)

Most people never wait this long. This is why large items frequently arrive thawed.

Palletized or Boxed Items

200 x 500g meals packed in boxes on a pallet:

Here’s where it gets really interesting. Even if each individual meal is frozen solid in its container, once you pack them in boxes and stack them on a pallet:

• The boxes create thermal barriers
• Air circulation is restricted
• The pallet core becomes insulated
• Items in the middle can take 2-3 times longer to temper

TOTAL: 48-72+ hours after palletization

Critical mistake: People freeze individual items, then immediately box and palletize them for collection the next day. The items in the middle of the pallet haven’t completed Phase 5.

Best practice: Freeze items individually FIRST (allow full 24-48 hours). Then pack/palletize at least 24-48 hours before dispatch to allow the packed configuration to complete Phase 5.

Products That Are Exceptions

Ice cream (commercial): Already manufactured and stored at -18°C or colder. Already at Phase 5. Can be dispatched immediately.

Pre-frozen commercial products: Items you bought frozen from a store that have been stored properly at -18°C continuously. Already at Phase 5.

Re-freezing previously frozen items: If items thawed and you’re re-freezing them, they still need to go through all 5 phases again. Don’t assume they’ll freeze faster because they were frozen before!

What BLOCKS or SLOWS Freezing

Understanding what prevents or dramatically slows proper freezing is just as important as understanding the phases themselves.

1. Packaging and Insulation 🎯

The problem:
Any packaging around your product creates a thermal barrier that slows heat transfer.

Examples:

• Thick plastic containers vs thin containers: Thick can take 50% longer
• Wrapped in plastic wrap then frozen: Adds hours to the process
• In cardboard boxes: Can double the freezing time
• Palletized: Can triple the time for items in the center

What to do:

• Freeze items BEFORE packaging when possible
• Use thin-walled containers
• Ensure good air circulation around items
• Allow extra time if you must freeze after packaging

2. Poor Air Circulation 🌬️

The problem:
Freezing works by cold air removing heat from your product. No air circulation = much slower freezing.

Examples:

• Chest freezer packed completely full: Items take 2-3x longer
• Items stacked directly on top of each other: Bottom items take much longer
• Items pressed against freezer walls: Can be slower than items with air flow

What to do:

• Don’t overfill your freezer (leave 20-30% empty space)
• Space items apart when initially freezing
• Use shelving racks in chest freezers
• Point fans at items (in walk-in freezers)

3. Incorrect Freezer Temperature 🌡️

The problem:
Your freezer needs to be at least -18°C to freeze items properly. Many home freezers run warmer.

Examples:

• Freezer at -12°C instead of -18°C: Can take 50-70% longer
• Freezer that cycles on/off frequently: Inconsistent temperatures extend time dramatically
• Frost-free freezers during defrost cycle: Temperatures rise temporarily

What to do:

• Check your freezer temperature with a proper thermometer
• Adjust settings to -18°C or colder
• For commercial operations, use blast freezers (-30°C to -40°C) to dramatically speed up the process

4. Product Composition 🧂

The problem:
Not all products freeze at the same temperature. The freezing point depends on what’s IN the product.

Science bit:

• Pure water: Freezes at 0°C
• Salty water: Freezes at -2°C to -6°C (depending on salt content)
• Sugary solutions: Freeze at -1°C to -5°C
• High-fat products: Can resist freezing down to -15°C
• Alcohol-containing products: Much lower freezing points

Examples of slower-freezing products:

• Curries and stews (salt, spices, fats): Take longer than plain vegetables
• Ice cream (high fat, high sugar): Needs very cold temperatures
• Fatty meats: Take much longer than lean meats
• Sauces with cream or alcohol: Significantly slower

What to do:

• Know your product composition
• Allow extra time for high-fat, high-salt, or high-sugar products
• Consider product design (maybe portion into smaller containers)

5. Volume and Thickness 📏

The problem:
Heat has to travel from the center to the outside. Large, thick products take exponentially longer.

The math:
Doubling the thickness doesn’t double the freezing time – it quadruples it! This is because heat has to travel further AND through material that’s already partially frozen.

Examples:

• 2cm thick lasagna: 12 hours to Phase 5
• 4cm thick lasagna: 48+ hours to Phase 5
• Thin burger patties: 6-8 hours
• Thick meatloaves: 36-48 hours

What to do:

• Portion large items into smaller containers
• Use shallow containers rather than deep ones
• Flatten items (like soups in ziplock bags laid flat) for faster freezing
• Remember: Many small items freeze MUCH faster than one large item

6. Starting Temperature 🌡️

The problem:
The warmer your product starts, the longer Phase 1 takes, and this adds to total time.

Examples:

• Room temperature (20°C): Full timeline as shown above
• Fridge temperature (4°C): Reduce Phase 1 by 30-40%, saving several hours
• Lukewarm from cooking (40°C): Add 50-100% to Phase 1

What to do:

• Pre-chill items in the fridge before freezing if possible
• Let cooked items cool to room temperature first (but not longer than food safety allows)
• Plan ahead – cooling in fridge overnight, then freezing, can save significant time

The Probe Test (Most Accurate) ✅

What you need:
A calibrated digital temperature probe or thermometer designed for food use.

How to do it:

1. Remove one sample item from your batch
2. Insert the probe into the CENTER (this is critical – not near edges)
3. Wait for reading to stabilize
4. Reading should be -18°C or colder throughout

What the results mean:

• -18°C or colder: ✅ Ready for dispatch (completed Phase 5)
• -12°C to -18°C: ⚠️ Technically solid but not fully tempered (still completing Phase 5)
• -5°C to -12°C: ❌ Still in late Phase 4, needs more time
• -2°C to -5°C: ❌ Still in mid Phase 4, definitely not ready
• 0°C or above: ❌ Still in Phase 2 or 3, completely not ready

Important:
The probe must go to the CENTER. Surface temperature is meaningless – the surface is always colder than the center.

The Physical Tests (Less Reliable But Useful)

Test 1: The Flex Test

• Squeeze or flex the container
• If ANYTHING moves, squishes, or sloshes → NOT READY
• Must be completely rigid throughout

Test 2: The Thump Test

• Knock on the container with your knuckle
• Should sound solid like knocking on wood
• If it sounds hollow or you feel movement → NOT READY

Test 3: The Cut Test (Destructive)

• Sacrifice one item from your batch
• Cut it in half with a knife
• Look at the center
• Should be uniformly frozen solid throughout
• If center looks different than edges → NOT READY

Test 4: The Time Test (Most Practical)

• Simply wait the proper amount of time based on your product size
• See the timelines above
• When in doubt, add 24 more hours

❌ Mistake #1: “I froze it overnight”

The problem:
“Overnight” is typically 8-12 hours. Looking at our timelines above, this is enough for small items but nowhere near enough for medium or large items.

The fix:

• Small items (500g): Minimum 24 hours
• Medium items (2-3kg): Minimum 48 hours
• Large items (5kg+): Minimum 72 hours
• Plan accordingly!

❌ Mistake #2: “It feels frozen solid”

The problem:
The outside is ALWAYS colder than the inside. Something can feel frozen solid but still have a liquid or semi-frozen center.

The fix:
Use the probe test. Check the CENTER temperature. Feeling is not reliable.

❌ Mistake #3: “Wrapping items then freezing”

The problem:
Wrapping creates insulation. Insulation slows freezing. Items wrapped tightly in plastic wrap, foil, or placed in insulated containers take much longer to freeze.

The fix:
Freeze FIRST, then wrap for transport. Or if you must wrap first, add 50-100% more time.

❌ Mistake #4: “Packing/palletizing immediately after freezing individual items”

The problem:
Individual items might be at Phase 5, but once you pack them tightly in boxes or palletize them, you create a new thermal environment. The center of the pallet hasn’t reached equilibrium.

The fix:
After packing/palletizing, allow another 24-48 hours in the freezer before dispatch.

❌ Mistake #5: “My freezer is set to the coldest setting”

The problem:
Many home freezers on “coldest setting” still only reach -12°C to -15°C, not the proper -18°C needed for efficient freezing and storage.

The fix:
Use a thermometer to check actual temperature. Consider upgrading to a commercial freezer if regularly dispatching frozen goods.

❌ Mistake #6: “I’ll freeze it faster by putting hot food straight in the freezer”

The problem:
This is terrible for several reasons:

• Raises the temperature of everything else in the freezer
• Can cause partial thawing of other items
• Creates ice crystals and frost buildup
• Actually slows the overall freezing process
• Food safety risk

The fix:
Cool hot food to room temperature first (within food safety guidelines – typically 2 hours maximum), preferably chill in fridge first, THEN freeze.

❌ Mistake #7: “I’m re-freezing something that was already frozen, so it’ll be quick”

The problem:
Once something thaws, it has to go through all 5 phases again from scratch. Previous freezing doesn’t “speed up” re-freezing.

The fix:
Treat re-frozen items like fresh items – full timeline applies. Better yet, avoid thawing and re-freezing when possible (quality deteriorates anyway).

Scenario 1: Goods Only at Phase 4 (Solid But Not Tempered)

You dispatch items that are solid but only just finished Phase 4:

• Center temperature: -8°C
• Edge temperature: -18°C
• Average temperature: -13°C

During transport in our -12°C truck:

• Brief exposure during loading (30 seconds at 25°C ambient)
• Doors opening at each delivery stop (20 stops, 20 seconds each)
• Brief exposure during unloading (30 seconds)

What happens:

• The edges stay frozen (they’re at -18°C)
• But the center (at -8°C) is vulnerable
• Brief warm exposures cause the temperature gradient to shift
• Center warms slightly, edges warm slightly
• Net result: Center reaches -2°C to 0°C
• Product partially thaws from the inside

Even though our truck was perfect at -12°C the whole time!

Scenario 2: Goods Fully at Phase 5 (Properly Tempered)

You dispatch items that completed Phase 5:

• Center temperature: -18°C
• Edge temperature: -18°C
• Uniform temperature throughout: -18°C

Same transport scenario:

• Brief exposures during loading/unloading
• Doors opening at stops

What happens:

• Product has a 6-degree buffer (-18°C starting point vs -12°C truck)
• Brief warm exposures barely affect it
• Center and edges both have thermal mass at proper temperature
• Product stays well within frozen range
• Arrives perfectly frozen

This is what proper preparation looks like.

For Small Items (500g containers):

Day 1 (Monday):

• Morning: Prepare and cook items
• Afternoon: Cool to room temperature
• Evening: Place in freezer (starting Phase 1)

Day 2 (Tuesday):

• Items progressing through Phases 1-4
• Don’t touch them!

Day 3 (Wednesday):

• Morning: Items should be at Phase 5
• Can pack for transport if needed
• Evening: Book collection for Thursday or later

Earliest safe dispatch: 48 hours after freezing started

For Medium Items (2-3kg tubs):

Day 1 (Monday):

• Morning: Prepare items
• Afternoon: Cool to room temperature or chill in fridge overnight
• Evening: Place in freezer if at room temp

Day 2 (Tuesday):

• Items progressing through early phases
• Still very much not ready

Day 3 (Wednesday):

• Items in mid to late Phase 4
• Still not ready for dispatch

Day 4 (Thursday):

• Morning: Items should be approaching or at Phase 5
• Do probe test to confirm
• Can pack if ready

Day 5 (Friday):

• Safe to dispatch if probe test confirmed -18°C

Earliest safe dispatch: 72 hours minimum, 96 hours safer

For Large Items or Palletized Goods:

Day 1 (Monday):

• Prepare and begin freezing individual items

Day 2-3 (Tuesday-Wednesday):

• Individual items completing their freeze cycles

Day 4 (Thursday):

• Individual items should be at Phase 5
• Now pack/palletize them
• Packed pallet goes back in freezer

Day 5-6 (Friday-Saturday):

• Packed pallet completing Phase 5 as a unit

Day 7 (Sunday):

• Earliest safe dispatch

Earliest safe dispatch: 5-7 days from start