Extrusion Test

What is the real difference between forward and back extrusion?

Forward extrusion pushes the sample out through a small hole at the bottom of the container — for pastes and semi-solids, measuring extrusion resistance (spreadability/firmness). Back extrusion pushes a plunger into an open container full of sample, which flows up past the plunger edge — for liquids and semi-liquids, measuring consistency and adhesiveness. The probe moves the same way; the container and reading differ.

Which foods can the Ottawa bulk compression kit test?

It suits any granular, flaky or irregular solid food: cereal, potato chips, prawn crackers, crisp biscuits, puffed rice, beans, berries, potato salad. It needs no per-piece positioning; one compression gives representative texture for the whole batch — good for QC screening and shelf-life work.

Is force fluctuation on an extrusion curve normal?

In forward extrusion, some fluctuation can come from air pockets released during filling. In bulk compression, periodic oscillation means brittle pieces are breaking one after another — a useful crispness signal, not an error. If fluctuation is large and irregular, recheck filling and temperature equilibration.

How do I set the correct trigger force?

Set it above background noise and probe weight, but not so high that early contact data is lost. Soft foods: about 5–20 gf. Semi-firm foods: around 50 gf. Run an empty test first to check background force, then set it so every test starts at the same point.

Can back extrusion compare dairy products with different fat levels?

Yes — back extrusion is a standard way to compare consistency across whole, reduced-fat and low-fat dairy. Keep the temperature, fill height and probe depth the same for every sample. Cream, yogurt and mayonnaise all have established back-extrusion methods to follow.