How to Maintain -18°C for 24-48 Hours When You’re Beyond Our Service Area
“Can you deliver to Ermelo?” “What about Plett?” “Can you ship to my farm near Graaff-Reinet?”
We get these questions weekly. The answer is often: “Our refrigerated trucks don’t service that area economically.” But that doesn’t mean your frozen food can’t get there professionally.
Let me explain the solution – and more importantly, the physics that makes it work.
The Service Gap Reality
The Frozen Food Courier operates mechanical refrigeration trucks in Gauteng and Western Cape – areas where multi-stop delivery routes make economic sense. But South Africa is big, and not everywhere has the delivery density to justify an expensive refrigerated truck making the trip.
Areas we DON’T currently service with refrigerated trucks:
- Rural towns beyond 100km from major metros
- Low-volume routes (< 5 regular customers)
- One-off deliveries to remote locations
- Emergency/rush deliveries where time matters
The amateur solution: Throw some ice packs in a cardboard box and hope. (This fails – we documented why in “The Ice Pack Delusion”)
The professional solution: Dry ice in proper insulation.
But here’s the critical distinction…
Why Dry Ice Works Where Water Ice Fails
The Thermodynamic Comparison
Let me show you the physics:
Water Ice Packs (The Ice Pack Delusion villain):
Melting point: 0°C
Latent heat of fusion: 334 kJ/kg
Problem: Melts AT 0°C - can't go colder
Operating range: 0°C (useless for frozen food requiring -18°C)
Typical package: 2-3 kg
Total cooling capacity: 835 kJ
Duration in cardboard box (R-value 0.7): 45-75 minutes
Duration in multi-stop courier operation: FAILS
Verdict: Thermodynamically inadequate for frozen food transport
Dry Ice (CO₂ Sublimation):
Sublimation point: -78.5°C
Latent heat of sublimation: 571 kJ/kg
Advantage: Sublimates at -78.5°C - 60°C COLDER than required
Operating range: -78.5°C warming to -18°C (perfect for frozen food)
Sensible heat warming: ~50 kJ/kg from -78.5°C to -18°C
Total effective capacity: ~620 kJ/kg (1.86× water ice)
Typical package: 3-5 kg
Total cooling capacity: 1,860-3,100 kJ (2.2-3.7× water ice capacity)
Duration in polytainer (R-value 3.0): 24-48 hours minimum
Duration for point-to-point delivery: SUCCEEDS
Verdict: Thermodynamically appropriate for single-delivery frozen transport
The Critical Differences
- Temperature capability: Dry ice operates 60°C colder than needed. Water ice operates 18°C WARMER than needed.
- Cooling capacity: Dry ice provides 1.86× more cooling per kilogram.
- Duration: With proper insulation, dry ice lasts 24-48 hours. Water ice lasts under 90 minutes.
- Application: Dry ice suits point-to-point delivery. Water ice suits… nothing frozen.
This is why dry ice doesn’t contradict our ice pack criticism – they’re completely different thermal systems for different applications.
The Three Prerequisites: Before You Even Touch Dry Ice
Dry ice is NOT a magic solution that compensates for poor preparation. It’s a professional thermal management tool that requires professional preparation.
Prerequisite 1: Goods Must Be Phase 5 Frozen
Remember from “Why Frozen Solid Takes Longer Than You Think”:
Freezing has 5 phases:
- Liquid cooling (getting cold)
- Nucleation (ice crystals forming)
- Recalescence (rapid crystal growth)
- Freezing phase (complete solidification)
- Solid cooling/tempering (equilibrium at -18°C throughout)
You MUST complete Phase 5 before using dry ice.
Why? Because dry ice maintains temperature – it doesn’t create it. If your product center is at -8°C (only Phase 4 complete), dry ice will maintain -8°C… and your food will be compromised.
Minimum freezing times before dry ice packaging:
- 500g items: 24 hours minimum
- 2-3kg items: 48 hours minimum
- 5kg+ items: 72 hours minimum
- After palletizing: Add another 24-48 hours
Use a temperature probe. Check the CENTER. It must read -18°C or colder. Not -12°C. Not -15°C. -18°C minimum.
If you skip this, dry ice cannot save you.
Prerequisite 2: Proper Insulation (Not Cardboard!)
Remember from “The Ultimate Guide to Packaging”:
Cardboard (R-value ~0.7) is inadequate even with dry ice. You need polytainer insulation (R-value 2.5-3.5) minimum.
Why this matters:
With cardboard box (R-value 0.7):
Heat infiltration at 35°C ambient, targeting -18°C:
Q = (1/0.7) × 0.8 m² × 53K = 61W
5kg dry ice capacity: 3,100 kJ
Duration: 3,100 kJ / (61W × 3600s/hr) = 14 hours
MAYBE adequate for same-day delivery. NOT adequate for overnight or longer.
With polytainer (R-value 3.0):
Heat infiltration same conditions:
Q = (1/3.0) × 0.8 m² × 53K = 14W
Same 5kg dry ice:
Duration: 3,100 kJ / (14W × 3600s/hr) = 61 hours
Adequate for 24-48 hour delivery window with safety margin.
Polytainers are non-negotiable for dry ice use.
Prerequisite 3: Understanding the Application
Dry ice is for:
- ✅ Point-to-point delivery (single destination)
- ✅ 24-48 hour delivery windows
- ✅ Areas beyond refrigerated truck economics
- ✅ Customer self-collection with professional packaging
- ✅ Air freight (with limitations)
Dry ice is NOT for:
- ❌ Multi-stop courier routes (use mechanical refrigeration)
- ❌ Deliveries beyond 72 hours (dry ice depletes)
- ❌ Situations where you don’t have polytainers
- ❌ Compensating for inadequate freezing (won’t work)
If you need multi-stop capability or extended range beyond 48 hours, you need mechanical refrigeration. Different physics, different application.
How Much Dry Ice Do You Need?
Let’s calculate based on South African conditions:
The Formula
Required dry ice (kg) = (Heat infiltration rate × Duration) / Dry ice cooling capacity
Where:
Heat infiltration rate = (U × A × ΔT)
U = Thermal conductivity (1/R-value)
A = Surface area of container (m²)
ΔT = Temperature difference (ambient - target)
Dry ice cooling capacity ≈ 620 kJ/kg
Worked Examples
Example 1: Johannesburg Summer (Worst Case)
Conditions:
- Ambient temperature: 35°C
- Target temperature: -18°C
- Temperature difference: 53K
- Polytainer: 30L, R-value 3.0, surface area 0.8 m²
- Delivery duration: 24 hours
- Safety margin: 50%
Heat infiltration:
Q = (1/3.0 W/m²·K) × 0.8 m² × 53K = 14.1W
24-hour heat load:
Energy = 14.1W × 86,400 seconds = 1,218 kJ
Dry ice needed (theoretical):
Mass = 1,218 kJ / 620 kJ/kg = 1.96 kg
With 50% safety margin:
Mass = 1.96 × 1.5 = 2.94 kg
Recommendation: 3-4 kg dry ice for 24-hour summer delivery
Example 2: Cape Town Winter (Best Case)
Conditions:
- Ambient temperature: 15°C
- Target temperature: -18°C
- Temperature difference: 33K
- Same polytainer specifications
- 24 hour duration
Heat infiltration:
Q = (1/3.0) × 0.8 × 33 = 8.8W
24-hour heat load:
Energy = 8.8W × 86,400 = 760 kJ
Dry ice needed (theoretical):
Mass = 760 / 620 = 1.23 kg
With 50% safety margin:
Mass = 1.23 × 1.5 = 1.85 kg
Recommendation: 2-3 kg dry ice for 24-hour winter delivery
Example 3: Air Freight (JHB to CPT)
Conditions:
- Duration: 6-8 hours door-to-door
- Ambient: 25°C average
- Same polytainer
6-hour heat load:
Energy = 11.5W × 21,600 seconds = 248 kJ
Dry ice needed:
Mass = 248 / 620 = 0.4 kg
With 100% safety margin (air freight variability):
Mass = 0.4 × 2 = 0.8 kg
Recommendation: 1-1.5 kg dry ice for same-day air freight
Note: Air transport restrictions typically limit to 2.5kg dry ice per package
Quick Reference Table
| Duration | Summer (Gauteng) | Winter (Cape) | Air Freight |
|---|---|---|---|
| 6-8 hours | 1-2 kg | 0.5-1 kg | 1-1.5 kg |
| 12 hours | 2-3 kg | 1-2 kg | N/A |
| 24 hours | 3-4 kg | 2-3 kg | N/A |
| 48 hours | 5-7 kg | 4-5 kg | N/A |
Rule of thumb: 1.5-2 kg per 12 hours in summer, 1 kg per 12 hours in winter, with 50% safety margin.
Critical Safety Requirements
⚠️ Dry ice is safe when used properly, dangerous when mishandled.
Physical Hazards
1. Cold Burns (-78.5°C)
- Never touch dry ice with bare hands
- Use insulated gloves or tongs
- Can cause frostbite in seconds
- Wrap in newspaper if handling unavoidable
2. CO₂ Asphyxiation Risk
- Dry ice sublimates to CO₂ gas
- Heavier than air (sinks to floor level)
- Displaces oxygen in confined spaces
- Can cause unconsciousness/death
NEVER:
- Transport in sealed vehicle cabin
- Store in sealed cold rooms
- Use in unventilated spaces
- Allow accumulation in low areas
ALWAYS:
- Transport in ventilated vehicles (windows open, or in cargo area)
- Store in well-ventilated areas
- Place warning labels on packages
- Provide ventilation instructions to recipients
Packaging Safety
1. Pressure Release Required
- CO₂ gas builds up as dry ice sublimates
- Sealed containers can explode
- Polytainers MUST have pressure release valve or loose-fitting lid
- Never seal completely airtight
2. Product Separation
- Never place dry ice in direct contact with food
- Wrap dry ice in newspaper or place in separate compartment
- Can cause freeze burns on food surface
- Can affect food quality
Air Transport Restrictions
If using air freight:
- Maximum 2.5 kg dry ice per package (typical airline limit)
- Must be declared as dangerous goods
- Special labeling required: “Carbon Dioxide, Solid (Dry Ice), UN1845”
- Net weight of dry ice must be marked on package
- Package must allow CO₂ gas to escape
Check specific airline requirements before booking.
Step-by-Step: Professional Dry Ice Packaging
Equipment Needed
Essential:
- Polytainer (30-50L, R-value 3.0+) with pressure release
- Dry ice (calculated quantity + 20% safety margin)
- Insulated gloves or tongs
- Newspaper or packing paper
- Packing tape
- Temperature data logger (optional but recommended)
Optional:
- Cardboard outer box (protection during handling)
- Bubble wrap (cushioning)
- Additional insulation wrap
The Process
Step 1: Verify Goods Are Phase 5 Frozen
CRITICAL CHECKPOINT:
- Use temperature probe
- Check CENTER of largest item
- Must read -18°C or colder
- If not -18°C, STOP and continue freezing
Do not proceed until this is confirmed. Dry ice cannot fix inadequate freezing.
Step 2: Prepare Polytainer
- Clean and dry polytainer interior
- Ensure pressure release valve functions
- Place newspaper/packing paper in bottom (cushioning)
- Work in cool environment if possible
Step 3: Load Frozen Goods
- Remove goods from freezer immediately before packing
- Work quickly (< 5 minutes from freezer to sealed)
- Place heaviest items on bottom
- Arrange for good space utilization
- No large air gaps between items
Step 4: Add Dry Ice (Properly)
Dry Ice Placement Strategy:
Bottom layer: None (goods sit on newspaper cushion)
Side distribution: 60% of dry ice around sides
Top layer: 40% of dry ice on top
Why this works:
- Cold CO₂ gas sinks naturally
- Top placement ensures gas flows down through cargo
- Side placement maintains edge temperature
- Bottom is coldest naturally (cold air sinks)
Handling procedure:
- Use insulated gloves
- Wrap each dry ice piece in 2-3 sheets newspaper
- This prevents direct contact with goods
- Also slows sublimation rate slightly
- Never unwrap or touch dry ice directly
Step 5: Fill Air Gaps
- Crumpled newspaper around/between items
- Bubble wrap for fragile items
- Fill to top – polytainer should be FULL
- No large empty air spaces
- Lid should press down on contents
Step 6: Add Temperature Logger (If Using)
- Place in center of cargo (most vulnerable location)
- Set to log every 5-10 minutes
- This provides evidence of temperature maintenance
- Valuable for insurance/verification
Step 7: Seal and Label
Sealing:
- Close polytainer lid securely
- Ensure pressure release valve is functional
- DO NOT tape completely airtight
- Gas must be able to escape
Labeling (Large, Clear Labels):
- "FROZEN GOODS - CONTAINS DRY ICE"
- "⚠️ HANDLE WITH CARE - COLD BURNS RISK"
- "VENTILATION REQUIRED - DO NOT OPEN IN CONFINED SPACE"
- "DRY ICE WEIGHT: X.X KG" (required for air freight)
- Delivery address and contact details
- "THIS WAY UP" arrows
Step 8: Optional Outer Box
- Place polytainer in cardboard outer box
- Add cushioning (newspaper, bubble wrap)
- This protects polytainer during rough handling
- Label outer box identically
Step 9: Immediate Dispatch
- Hand to courier immediately after sealing
- Every hour at room temperature reduces dry ice life
- Inform courier about dry ice contents
- Provide ventilation and handling instructions
What Recipients Should Know
Provide these instructions with every shipment:
RECEIVING INSTRUCTIONS FOR DRY ICE PACKAGE:
1. VENTILATION REQUIRED
- Open package outdoors or well-ventilated area
- Never open in small enclosed rooms
- CO₂ gas is heavier than air and displaces oxygen
2. HANDLING
- Use gloves when removing dry ice
- Never touch dry ice with bare hands
- Can cause severe cold burns
3. DISPOSAL
- Place remaining dry ice in well-ventilated area
- Allow to sublimate naturally (evaporate)
- Never dispose in sealed containers or drains
- Usually dissipates within 6-24 hours
4. PRODUCT STORAGE
- Transfer frozen goods to freezer immediately
- Verify products are still frozen solid
- Temperature logger data available on request
5. QUESTIONS?
Contact: hello@thefrozenfoodcourier.co.za
When to Use Each Solution: The Decision Matrix
How do you know whether you need dry ice, mechanical refrigeration, or something else?
Use Mechanical Refrigeration (Our Core Service) When:
- ✅ Multiple delivery stops (5+ locations)
- ✅ Regular recurring deliveries
- ✅ Areas within our Gauteng/Western Cape service zones
- ✅ Delivery windows beyond 48 hours
- ✅ You need documented R638 compliance
- ✅ Product value justifies professional service cost
Why: Mechanical refrigeration maintains -18°C to -20°C continuously for 15-30 stops per route. Designed for multi-stop courier operations.
Cost: R270 per delivery within service areas
Use Dry Ice (Our Packaging Service) When:
- ✅ Single destination delivery
- ✅ 24-48 hour delivery window
- ✅ Location beyond our refrigerated truck service area
- ✅ One-off or occasional shipments
- ✅ Customer willing to self-collect
- ✅ Air freight required (weight restrictions)
Why: Dry ice in polytainers maintains temperature for point-to-point delivery where mechanical refrigeration isn’t economical.
Cost: R350-550 depending on dry ice quantity and destination
NEVER Use Water Ice Packs When:
- ❌ Transporting frozen food (they operate at 0°C, not -18°C)
- ❌ Multi-stop routes (deplete in 45-75 minutes)
- ❌ Anything requiring professional cold chain
- ❌ Ever, for frozen food transport
Why: Thermodynamically inadequate as documented in “The Ice Pack Delusion”
Our Dry Ice Packaging Service
We understand you’re beyond our refrigerated truck service area. But that doesn’t mean you can’t get professional frozen delivery.
What We Provide
Option 1: DIY with Our Guidance (Free)
- This article + our other guides
- Email support for calculations
- Recommendations for dry ice suppliers
- Packaging material sources
- No charge – we want frozen food done right
Option 2: Professional Packaging Service
- You ship frozen goods to our facility
- We verify goods are Phase 5 frozen (-18°C probe test)
- We package professionally in polytainers with correct dry ice quantity
- You/your courier collects for final delivery
- Temperature logger included
- Cost: R350-400 for local, R450-550 for regional
Option 3: Complete Service with Partner Courier
- Same professional packaging
- We arrange courier to final destination
- Partner couriers briefed on dry ice handling
- Extends our effective range to most of South Africa
- Cost: Packaging + courier fee (quoted per route)
Option 4: Air Freight (JHB-CPT)
- Professional packaging for air transport
- Coordination with Safe Fly air cargo
- Same-day delivery Johannesburg to Cape Town
- Airline-compliant dry ice declaration
- Cost: R800-1,200 depending on weight
Why Use Our Service vs DIY?
You might DIY if:
- You have access to proper polytainers
- You can source food-grade dry ice
- You understand the calculations
- You ship regularly (worth investment in equipment)
- You’re confident in your preparation
Use our service if:
- You’re shipping one-off or occasionally
- You don’t want to invest in polytainers
- You want professional verification
- You need temperature data logging
- You want someone else handling dry ice safely
Common Questions
Q: Can dry ice replace mechanical refrigeration for multi-stop routes?
No. Dry ice is for point-to-point delivery. Multi-stop routes need mechanical refrigeration because:
- Door openings introduce heat load that dry ice struggles with
- Dry ice depletes over 24-48 hours
- Can’t refill dry ice mid-route
- R638 compliance requires mechanical refrigeration for commercial multi-stop operations
Different physics, different application.
Q: Why don't you just deliver everywhere with dry ice packages?
Because mechanical refrigeration is superior for multi-stop routes:
- Continuous active cooling (doesn’t deplete)
- Recover temperature after each door opening
- R638 compliant with documented monitoring
- More reliable for daily route operations
Dry ice is the right solution for extending range beyond truck economics. Not a replacement for professional refrigerated transport.
Q: Can I use dry ice in cardboard boxes?
Technically yes, but duration drops dramatically:
- Cardboard R-value ~0.7 vs polytainer 3.0
- 4× faster heat infiltration
- Dry ice depletes in 6-12 hours instead of 24-48 hours
- Only viable for very short same-day deliveries
For any overnight or longer delivery, polytainers are non-negotiable.
Q: How much does dry ice cost?
Q: Where do I get dry ice?
Contact us for recommendations. Food-grade dry ice suppliers in major metros:
- Johannesburg: Industrial gas suppliers
- Cape Town: Same
- Smaller towns: Often available from larger medical facilities or industrial suppliers
Order 24 hours ahead – most suppliers don’t stock, they produce on demand.
Q: What if the dry ice runs out during delivery?
This is why safety margins matter:
Risk mitigation:
- Calculate for actual duration
- Add 50% safety margin to dry ice quantity
- Use proper polytainer insulation (R-value 3.0+)
- Ship goods Phase 5 frozen (-18°C throughout)
Properly prepared packages maintain temperature even after dry ice depletes because:
- Goods have thermal mass at -18°C
- Insulation slows warming
- Typical warming rate post-depletion: 2-3°C per hour
- Gives 4-6 hour buffer before goods reach -12°C (compromised)
This is why we include temperature loggers – you can verify performance.
Q: Can I mix dry ice with gel packs?
Q: My goods partially thawed even with dry ice. What happened?
Q: My goods partially thawed even with dry ice. What happened?
Most common causes (in order):
- Goods weren’t Phase 5 frozen before packaging (90% of cases)
- Center was only -8°C, not -18°C
- Dry ice maintained -8°C, goods compromised
- Solution: Proper probe testing before packaging
- Insufficient dry ice quantity
- Underestimated delivery duration
- Didn’t account for summer temperatures
- Solution: Use our calculator, add safety margin
- Poor insulation (cardboard instead of polytainer)
- Heat infiltration 4× faster
- Dry ice depleted prematurely
- Solution: Proper polytainers
- Large air gaps in package
- Warm air pockets inside
- Reduced effective cooling
- Solution: Fill completely, no gaps
Q: Can I reuse dry ice packages?
Polytainers: Yes, indefinitely if cleaned Dry ice: No, it sublimates completely – order fresh for each shipment Temperature loggers: Yes, if rechargeable type
Q: Does altitude affect dry ice performance?
Slightly, but less than water ice:
- Lower pressure at altitude = slightly faster sublimation
- Effect: 5-8% faster at Johannesburg vs Cape Town
- Solution: Already built into our safety margins
Main altitude effect is ambient temperature:
This matters more than pressure effect
Johannesburg summer: Higher temps = more heat load
The Complete Frozen Delivery Ecosystem
Understanding how all our guidance works together:
Phase 1: Freezing (Read full article)
- Complete 5 phases of freezing
- Minimum 24-72 hours depending on size
- Center must reach -18°C (Phase 5 complete)
- Probe test verification
Phase 2: Packaging (Read full article)
- Polytainers (not cardboard) for dry ice
- Virgin double-walled cardboard for ice packs (if using in refrigerated trucks)
- Fill all air gaps
- Seal immediately
Phase 3: Thermal Management (This article)
- Mechanical refrigeration for multi-stop routes (our core service)
- Dry ice for point-to-point beyond service area
- Never water ice packs for frozen food
Phase 4: Transport
- Proper handling by courier
- Ventilation (if dry ice)
- Temperature monitoring
- Verification on arrival
The Bottom Line
Dry ice is a legitimate professional solution for frozen food delivery when:
- ✅ You’re beyond refrigerated truck service areas
- ✅ You need point-to-point delivery (single destination)
- ✅ Delivery window is 24-48 hours
- ✅ Goods are properly prepared (Phase 5 frozen, polytainer packaging)
Dry ice is NOT a substitute for:
- ❌ Mechanical refrigeration on multi-stop routes
- ❌ Proper freezing preparation
- ❌ Adequate insulation
The physics is different from water ice packs (which fail thermodynamically). The application is different from mechanical refrigeration (point-to-point vs multi-stop). But for its intended use case – extending frozen delivery to areas beyond refrigerated truck economics – dry ice works professionally when used correctly.
We don’t service everywhere with refrigerated trucks because physics and economics both matter. But we can help you get professional frozen delivery even in areas we don’t reach directly – through proper dry ice packaging preparation, guidance, or our complete packaging service.
The physics is real. The safety requirements are real. The preparation steps are non-negotiable. And the results, when done properly, are professional frozen food delivery beyond our refrigerated truck footprint.
The physics applies equally whether using dry ice sublimation or mechanical compression cycles. Both are professional solutions for different duty cycles. Both require proper preparation. And both fail when shortcuts are taken.
The Frozen Food Courier operates specialized temperature-controlled last-mile logistics in Gauteng and Western Cape, South Africa. We run mechanical refrigeration trucks maintaining -18°C to -20°C for multi-stop routes because that’s what the physics demands for professional courier operations. But we recognize not every location justifies an expensive refrigerated truck visit. For areas beyond our refrigerated truck service area, we provide dry ice packaging services and technical guidance – because frozen food logistics should be done professionally regardless of location. Whether you need guidance for DIY packaging or want our professional packaging service, we’re here to help you get frozen food delivered professionally – even beyond our refrigerated truck service area.
Related Articles
- Why “Frozen Solid” Takes Longer Than You Think – Understanding the 5 phases of freezing and why Phase 5 completion is critical
- The Ultimate Guide to Packaging Frozen Foods – Polytainers, insulation R-values, and proper packaging techniques
- The Ice Pack Delusion – Why water ice packs fail thermodynamically for frozen food transport
