SOP: Maturity Grading of Peas and Lima Beans by Brine Density

GIFSQ — Global Institute for Food Safety & Quality

Principle

As peas and lima beans mature, their density increases; shelled peas are blanched and floated in brines of stated density, and the proportion sinking in each brine is counted. The United States Standards for grades of canned peas fix, for each grade, the maximum percentages sinking in the prescribed salt solutions (11%, 13%, 13½% or 15% as applicable), while the canner’s salometer scale gives the brine densities for successive separations of peas and lima beans.

Apparatus required

• Vessels for the brines
• Canner’s salometer, for checking brine density

Reagents

a. Common salt (sodium chloride).

b. Water.

c. Brines of the required salometer densities (see Calculation below).

Sample preparation

Blanch the shelled peas before the floatation test.

Procedure

Float the blanched peas in brine of the first density and separate the floaters from the sinkers

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Float the sinkers in brine of the next higher density

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Count the number of peas sinking in each brine and express as a percentage of the total count

Calculation

United States Standards for grades of canned peas (maturity and tenderness):

Sweet (wrinkled) peas:

• Grade A (Fancy grade): not more than 12% by count sink in an 11% salt solution, and not more than 2% sink in a 13% salt solution.
• Grade B (Extra standard): not more than 15% by count sink in a 13% salt solution, and not more than 4% sink in a 15% salt solution.
• Grade C (Standard): not more than 10% by count sink in a salt solution of 15%.

Alaska or smooth-seeded (early) peas:

• Grade A (Fancy grade): not more than 20% by count sink in an 11% salt solution, and not more than 2% sink in a 13% salt solution.
• Grade B (Extra standard): not more than 30% by count sink in a salt solution of 13½% (printed “134%”), and not more than 8% sink in a 15% salt solution.
• Grade C (Standard): not more than 10% by count sink in a salt solution of 16%.

Where,

• The Grade B brine for Alaska peas is printed as “134%”; carried as 13½%, consistent with the neighbouring grade limits.

Brine densities used for peas and lima beans (canner’s salometer scale, °S):

• Peas: 30° to 36° S for No. 1 Fancy; 35° to 42° S for No. 2 Choice; 38° to 46° S for No. 3 Standard and larger.
• Lima beans: first separation 43–47° S; second separation 47–60° S; third separation 60–70° S.

Suitability of potatoes for canning (specific gravity):

• Potatoes with a specific gravity below 1.075 can generally be canned without disintegration or sloughing during processing, even without the use of calcium salts.
• Sloughing can usually be prevented in specific gravity lots of 1.075 to 1.095 with added calcium salts.
• When the specific gravity exceeds 1.100, excessive sloughing occurs even with added calcium salts.

Precautions

• Blanch the peas uniformly before floatation.
• Check each brine density with the salometer before use.

References

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