Crate specifications turn on two numbers that appear on every data sheet and are regularly misunderstood. Both are more conditional than they look, and knowing what they leave out is more useful than knowing what they say.
Vent ratio
The percentage of the wall surface that is open. It is a real and useful number, and it does not tell you what most people assume.
What it does tell you: roughly how much air can move through the crate, and therefore how fast produce will cool. That is genuinely valuable during pre-cooling, which we covered in crates for pre-cooling after harvest.
What it does not tell you: whether fruit will bruise. Bruising comes from produce sitting over an opening, which is about hole size and floor pattern, not total open area. Two crates at thirty per cent vent ratio can behave completely differently for soft fruit, because one has many small holes and a ribbed floor and the other has a few large ones.
So: specify vent ratio for cooling, and hole geometry for bruising. They are separate numbers.
Stack height
How many crates can be stacked. Every crate has a figure, and every figure is stated without the condition that actually matters – for how long.
Soft produce under sustained load keeps deforming. So the meaningful specification is not a maximum height, it is a maximum height for a maximum dwell. A stack that is fine for two hours is not fine overnight, and the crate has not changed.
If you are writing a specification, write both numbers. It is the single most useful change you can make to a crate spec, and almost nobody does it. We made the same point in how to stack fruit crates so the bottom layer doesn’t bruise.
Also worth asking about
Whether the stack height is for loaded or empty crates. Empty crates nest and stack to a very different height. A figure quoted without saying which is ambiguous, and the empty figure is usually much larger.
Whether the crates interlock. An interlocking stack is more stable and gives a different effective height per layer. Compare like with like.
Two more numbers worth writing down
Nest ratio. How many empty crates occupy the space of one assembled crate. It governs return volume and storage, and it is the number that decides whether a pool or a return loop is viable. Crates with a poor nest ratio make every empty expensive to move.
Tare weight. What the crate weighs empty. It matters twice: it is dead weight on every outbound load, and it is what the operator lifts every time they handle it. A crate that is a kilo lighter is a kilo per crate on every truck and a meaningful reduction in effort across a shift.
Both are on most data sheets and both are usually ignored at specification time.
And one term that is misused constantly
“Food grade.” It is not a single standard and it does not mean the same thing to everyone who says it. What it should mean is that the material is intended for contact with food and that someone will say so in writing.
We went through the questions worth asking in food-contact questions to ask before buying PP crates. If a specification says food grade and nothing more, it is worth a follow-up.
What we can do
We make PP crates for fruit and vegetables and quote vent ratio with the hole geometry, and stack height with a dwell condition. Tell us the crop and how long a loaded stack stands, and we will specify – including when a lower stack that moves faster is the better answer.