Freezing and packing ice packs: how to do it right
Ice packs only work if they are properly frozen and properly placed in the box. In practice we see that most temperature complaints are not down to the product but to one of these two steps.
Freezing
Freeze the packs flat and separately at a minimum of minus 18 degrees. Not stacked: a stack freezes solid on the outside while the core stays liquid. Such a pack feels hard but delivers a fraction of the cooling capacity.
A 400 g pack is completely frozen through after 12 to 24 hours. For 1000 g, allow at least 24 hours. If you are short of freezer capacity, you are better off starting a day earlier than sending more packs.
Packing
Place the packs on top of the product, not underneath. Cold sinks: a pack at the top cools the whole box, a pack at the bottom mainly cools the base.
For a large box or a long transit time, distribute the packs: some on top and some along the sides. Make sure the packs do not touch the product directly if freezing is undesirable; place a sheet of cardboard or an insulated bag between them.
Filling remaining space
Air in the box is space in which heat circulates. Fill remaining space with filling material or choose a box size that suits your product. A full box holds temperature considerably longer than a half-full one.
How many packs
Rule of thumb for a thick-walled EPS box and an outside temperature of 25 degrees: one 400 g pack per 5 litres of volume for 24 hours of chilled transport. Double that for 48 hours or for frozen shipping. Always calculate with your longest transit time, not the average.
Freezer and planning
A freezer full of other food freezes packs through more slowly. Keep space free and preferably lay the packs in a single layer on a rack or shelf. That way cold air reaches the pack from all sides.
Plan your stock in two sets. While set one is in transit, set two is freezing. If you have many shipments per day, calculate how many packs you need at the same time and how much freezer space that requires. Check the freezer temperature now and then with a thermometer, especially if the door is opened often.
Pre-cooling product and box
A pack is meant to keep the box and the load cold, not to cool a warm product down first. Make sure the product is already at the desired temperature before you pack. A box that stands in a warm space is also better chilled beforehand. That way the cooling capacity of the packs goes to the transit time and not to cooling down.
Check before the box is closed
- Do the packs feel hard everywhere, including in the middle?
- Are the packs intact, without tears or leaks?
- Is the product not lying directly against a pack where that is not allowed?
- Has remaining space been filled, so that nothing can shift?
- Is the lid properly on the box and is the box properly sealed with tape?
- Do you know when the box will arrive, and is there someone to receive it?
Common mistakes
- Freezing packs for too short a time because the shipment is urgent.
- Freezing packs in a stack, so that the core stays liquid.
- Placing all packs at the bottom.
- Sending a large box with little in it, so that a lot of air remains.
- Shipping on a Friday without allowing for a weekend in transit.
Which pack and which box
For standard chilled shipping, a 400 g gel pack is a usual choice. You can find more about this pack on gel pack 400 gram, and the whole range is in gel packs. Unsure between a gel pack and a hard cooling element? Read cold plate or gel pack. For a lower temperature than your freezer can reach, look at cold packs or dry ice.
A properly frozen pack only helps in a well-insulated box. Take a look at the EPS boxes and read how long does a cold pack stay cold to work out your transit time. Do you want to measure the result? Then use a data logger.
Instructions for your team
Do you work with several people at the packing station? Then record the steps on a card at the packing bench: freeze packs flat, at least 12 hours, check for leakage, place on top, fill remaining space, lid and tape. A fixed routine prevents the packing from depending on who happens to be on shift, and makes it easier to trace mistakes if a complaint does come in.
After use
Let the pack thaw and dispose of it with the general waste. Do not cut the film open and do not rinse the gel down the sink, because it can thicken in the drain.
Frequently asked questions
Can I put packs in the fridge instead of the freezer?
Then they only cool down, and are much less cold than a frozen pack. For frozen shipping or long routes, you freeze the packs.
How do I know whether a pack is frozen through properly?
Feel whether it is hard everywhere, including in the middle. If the core is soft, it is not ready yet.
May I refreeze packs after thawing?
First check that the pack is intact. A pack with a leak or tear should be thrown away.
