SOP: Grading of Peas by Brine Floatation

GIFSQ — Global Institute for Food Safety & Quality

Principle

As peas mature, their density increases. When peas are placed in a brine of a stated specific gravity, the less mature peas float while the more mature, denser peas sink. By floatation in two brines of fixed specific gravity, peas are separated into ‘fancy’, ‘standard’, and ‘substandard’ (or ‘seconds’) grades.

Apparatus required

• Vessels to hold the two brines
• Hydrometer, for checking the specific gravity of the brines

Reagents

a. Common salt (sodium chloride).

b. Water.

c. Brine of 1.04 specific gravity: dissolve common salt in water, adding the salt until the specific gravity of the solution is 1.04.

d. Brine of 1.17 specific gravity: dissolve common salt in water, adding the salt until the specific gravity of the solution is 1.17.

Sample preparation

Grade the peas for size and blanch them before the floatation test.

Procedure

Place the sized and blanched peas in the brine of 1.04 specific gravity

↓

Remove the peas that float and set them aside as ‘fancy’ quality

↓

Transfer the peas that sank to the brine of 1.17 specific gravity

↓

Remove the peas that float and set them aside as ‘standard’ quality

↓

Designate the peas that sink in the 1.17 specific gravity brine as ‘substandard’ or ‘seconds’

Calculation

No calculation is involved; the test separates and grades the peas by density.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.