Unit picking in grocery: a challenge warehouses can no longer improvise

Wim Vermeir

Senior Sales Executive

LinkedIn →

August 27,2026

Grocery retail has long been assumed to be simpler than other logistics environments. Standardised products, regular flows, well-established references.

The reality, for anyone who has worked in a food replenishment warehouse, is precisely the opposite. Grocery concentrates some of the most demanding constraints in the entire supply chain, particularly when it comes to unit picking.

Four flows, four logics: the starting point for any serious thinking

Understanding the complexity of grocery logistics begins with accepting that not all products are handled the same way. Practitioners generally distinguish four categories.

• Full pallet: received as a pallet, stored as a pallet, despatched as a pallet. A direct flow with no complex handling.
• Full case: for high-velocity products, replenishment is carried out by the full carton.
• Unit picking: for products whose volume does not justify replenishment by the full case, the operator extracts one or more individual units
• Others : oversized items that do not fit standard racking and require separate handling.

In a real replenishment warehouse, all four flows coexist and must be consolidated before despatch. This is the first major challenge of grocery logistics.

Picking rules that common sense alone cannot enforce

What fundamentally sets grocery picking apart from other sectors is the composition constraints that govern order preparation. Two families of rules apply to every picker.

Product family segregation

Certain items cannot be placed near one another. Strawberries and laundry detergent, for instance. This is not purely a hygiene matter, it is a regulatory and commercial requirement whose breach can lead to product loss and customer complaints.

The stacking rule

In a picking tote, the order in which items are placed is not incidental. Eggs do not go in first if heavy items are to follow. The picking sequence must account for fragility and weight, which demands a level of orchestration from the control system that few manual solutions can consistently deliver.

Buffering and sequencing: why most warehouses need a second system

A grocery store replenishment order is often large enough to require multiple despatch containers. The time elapsed between picking the first and the last container within a single order can be considerable.

Yet at the point of loading, all those containers must be grouped together, in the correct order. This requires two distinct operations: buffering, holding containers until the full order is complete, and sequencing, releasing them in an order that aligns with the store’s replenishment logic.

Buffering and sequencing are not secondary options: they directly determine a warehouse’s ability to deliver to stores within the required timeframes.

Before comparing picking rates, a retailer would do well to ask whether the solution under consideration natively integrates buffering and sequencing, or whether it delegates them to third-party equipment. Because it is often in this articulation, more than in raw picking speed itself, that the real reliability of an installation is decided.

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