How Do You Measure Full-Fat vs Low-Fat Yogurt Consistency? A Back Extrusion Guide

A back extrusion test presses a plunger into an open container full of sample, and the sample flows up past the plunger's edge. It measures the resistance during the push-in stroke, and the force needed to overcome the sample's adhesion as the probe withdraws.

This method suits fluid and semi-fluid foods — yogurt, mayonnaise and cream all fall into this group. It uses the Back Extrusion Cell (BES) accessory, with the test mode set to distance (compression).

Testing full-fat and low-fat samples at the same temperature matters most. Fill height and probe immersion depth must also match, or differences may come from the procedure rather than the recipe.

The consistency index is the area under the positive force–displacement curve during the push-in stroke, reflecting overall thickness. A higher value means a thicker sample.

Adhesiveness is the negative-force area as the probe withdraws, reflecting the yogurt's stickiness and surface adhesion. Low-fat recipes commonly show lower consistency, and the change in adhesiveness should be watched alongside it.

When comparing full-fat and low-fat samples, look at both the consistency index and adhesiveness, and check whether the two groups' standard deviations overlap, so normal repeat-to-repeat variation isn't mistaken for a real recipe difference.