Crate types in potato storage: wood, plastic and steel compared

You rarely make the decision for a crate type from scratch. A bulk crate remains in use for years, a stock of one to two thousand crates ties up a lot of capital, and once you have committed to a material and a size, you usually stick with it for a long time. All the more annoying when it only becomes apparent after the first or second season that the crates do not suit the ventilation system or are difficult to clean.

This article compares the common crate types by material, ventilation, size and cost and provides guidance to help different farms decide.

First things first: loose or crate storage?

By volume, most potatoes in Germany are still stored loose, especially starch and processing potatoes in large, uniform batches. In the premium segment – table and seed potatoes – crates have become the standard. Almost all farms building new stores today plan crate storage for these segments. Practical estimates put the figure at 80 to 100% of new builds.

The reason is not nostalgia, but control. Crate storage divides the harvest into many individually movable batches. A large farm with many varieties and propagation stages can hardly keep fractions separate otherwise. And if a damp batch starts to deteriorate, you spot it early in the crate and can pull it out individually, whereas in bulk floor storage the damage may only be revealed by seeping water when half the batch is already affected. We cover the fundamental trade-off between storage systems separately; here the question is which crate to choose.

What a bulk crate needs to do

Before looking at materials, it is worth considering the requirements. A large potato crate must:

• be movable by forklift, individually and quickly, without shaking the tubers
• be stackable, in practice up to six crates high
• bear the weight of the crates stacked above it, so that the pressure does not rest on the tubers
• allow air through or channel it specifically, depending on the ventilation system in the store
• be easy to clean and maintain over many years

The last point pays off when stacking: Because the crates bear the weight, there is hardly any storage pressure on the tubers at the bottom. This is one of the biggest advantages over a high bulk pile, where the potatoes at the bottom bear the weight of the entire heap.

Typical crate sizes range from half a tonne to five tonnes. More than three quarters of the market, however, is between one and one and a half tonnes. This size has established itself as a good compromise between handling, batch size and stackability.

The material question: wood, plastic, steel

First, a point that may surprise some: The crate material has hardly any measurable effect on the tuber itself. Studies found no significant differences in weight loss between materials. So the decision is not about the potato, but about handling, hygiene, durability and cost. And that is where the materials differ considerably.

Wooden crates

Wood is the classic and still the standard in many stores. It is inexpensive to buy, can be repaired by replacing individual boards, and buffers moisture to some extent. In practice, wooden crates are often labelled directly, with chalk or stapled-on tags.

The weaknesses lie in hygiene. The rough, absorbent surface takes up moisture, then becomes heavier, and fungi and bacteria can survive in the pores and joints. If you store diseased produce in one season, the wood may carry the pathogens into the next. Thorough disinfection is laborious, and wood adds extra fire load to the store.

Plastic crates

Plastic plays to its strengths in hygiene. Smooth surfaces without absorbent pores are quick to clean and disinfect, which matters especially in the seed and premium segments. The crates are lightweight, dimensionally stable and therefore easy to stack, resulting in cleanly defined air channels in the stack. And they last a long time.

On the other hand, they are more expensive to buy. Older or inferior plastics can become brittle over time, especially under UV light or in the cold, and a damaged plastic crate usually cannot be patched as easily as a wooden one but has to be replaced.

Steel and metal-frame crates

Crates with steel frames or made of metal are extremely robust and durable, bear high stacking loads and are easy to clean. The price is high, as is the weight. One point to keep in mind: Cold metal surfaces are prime spots for condensation. Where moist air condenses on cold metal, it creates exactly the condensation that triggers rot. With proper climate control this is manageable, but it needs to be considered.

Ventilation determines the crate type

The most important technical point is often underestimated when choosing crates: The crate must match the store's ventilation system. There are two basic principles.

With room ventilation air is circulated through the room and flows around the stacks from the outside. This is simple and inexpensive, but cools slowly and unevenly. Ventilation times are longer, and moisture and heat can build up in the middle of large stacks, with a correspondingly higher risk of rot. For room ventilation, open, ventilated crates are sufficient.

With forced or pressure ventilation air is forced specifically through the crates. This cools and dehumidifies quickly and evenly. But this requires exactly the right type of crate: crates with closed side walls that form a tight air duct, and precise arrangement in the stack so that air does not escape sideways but flows through the produce. If you want pressure ventilation but buy open crates, you waste the entire advantage.

Many farms run both systems in parallel: wet or freshly harvested batches first go into forced ventilation for rapid drying and curing, the rest into room ventilation for long-term storage. For details on temperature management across these phases, see our article on the right temperature for storage.

Think in terms of lifetime costs

The purchase price per crate is only half the story. Crate storage is more expensive to run than bulk storage because each crate has to be filled, moved, labelled and emptied individually. In return you get separation of batches and better control.

Two cost items are often overlooked:

Cleaning and maintenance. Potato crates need to be cleaned and serviced every few years. This prevents overloaded or rotten crates from collapsing and, more importantly, prevents transmission of diseases from a previous season. This effort is greater for wood than for plastic or steel. If you factor this item into the material decision, the higher purchase cost of plastic often leads to a different conclusion than just looking at the purchase price.

Service life and replacement. A repairable wooden crate can be kept in service for a long time by replacing individual boards. A plastic crate often lasts longer in one piece, but if it breaks it is a total loss. Calculated over ten or fifteen years, it is not the purchase price that matters but the number of replacements required.

Decision aid: which crate for which farm

• Many varieties, high hygiene requirements, seed or premium produce: Plastic. Easy disinfection and dimensional stability outweigh the higher price, especially where pathogens have no place.
• Table potatoes, existing wooden crate system, limited budget: Wood remains viable as long as the cleaning regime is sound and diseased batches are consistently separated.
• Pressure-ventilated store: Crates with closed side walls, regardless of material. Open crates render forced ventilation ineffective.
• Room-ventilated store, large uniform batches: open, ventilated crates are sufficient, or reconsider the question of bulk versus crates.
• Very long service life, high stacking load: Steel or metal frame, keeping an eye on condensation on cold surfaces.

The underestimated factor: keeping track

There is a lot of talk about material and ventilation, too little about keeping track. In practice, the lost crate is a daily annoyance. Batches are labelled with chalk, but not always updated when moved. Then a different variety suddenly ends up in a half-empty row without it being noted on the storage plan. If you want to load a specific batch, you may end up searching for it on foot, climbing through rows and moving stacks.

This is exactly where an often untapped advantage of crate storage lies. Because each crate is an individually addressable unit, it can be located digitally. Instead of chalk and a large board on the wall, digital store management keeps track of which batch is in which row and stack, with variety, origin, harvest date and quantity. When the forklift driver moves a crate, it is recorded, often directly on the tablet on the forklift. The effect is twofold: The daily search effort is reduced, and the traceability that QS and other standards require anyway is created as a by-product. For details on exactly what documentation is required, see our overview of applicable standards.

Frequently asked questions

Wood or plastic for potato crates? The material has hardly any effect on the tuber. Plastic scores on hygiene, cleaning and durability, wood on purchase price and repairability. For seed and premium produce there is a strong case for plastic; for budget-conscious table potato farms, wood remains an option provided the cleaning regime is adequate.

What crate size is common? Most of the market is between one and one and a half tonnes per crate, with a range from half a tonne to five tonnes. One to one and a half tonnes is considered a good compromise between handling and batch size.

How high can potato crates be stacked? In practice up to six crates on top of each other. Because the crates bear the weight, there is hardly any storage pressure on the tubers.

Do I need special crates for forced ventilation? Yes. Forced or pressure ventilation only works with crates with closed side walls and precise stacking so that air flows through the produce rather than past it.

How often do potato crates need to be cleaned? Cleaning and maintenance are due every few years to prevent disease transmission from previous seasons and failure of rotten crates. The effort is greater for wood than for plastic or steel.