SOP: Measurement of Jelly Strength by the Cox–Higby Sag Method

GIFSQ — Global Institute for Food Safety & Quality

Principle

The method measures the percentage sag or slump occurring when a test jelly is removed from its supporting container and inverted upon a glass plate. The apparatus is based on the ridgelimeter principle developed by Lockwood and Hayes for determining the strength of gelatine and agar jellies.

Apparatus required

• Exchange Ridgelimeter
• Ridgelimeter glasses: Hazel-Atlas No. 85 tumblers, ground so that the inside height is exactly 3.125 in.; sidewalls extended about 0.5 in. (12 mm) higher with removable gummed paper sideboards — Scotch drafting tape 0.75 in. wide and 9.5 in. long may also be used, the strip covering 0.25 in. of the glass and extending 0.5 in. above the glass
• Micrometer screw: 32 threads to an inch, so that one revolution moves the point 0.03125 in., or 1% of the supported height of the jelly (equal to 1% sag); the glasses have a standard depth of 79.4 mm (3.125 in.)
• Square glass plate
• Tightly stretched clean wet wire (cheese cutter supplied along with the instrument)
• Spatula
• Stopwatch

Procedure — Preparation of jelly

Dissolve 48.8 g of tartaric acid in distilled water and make to 100 ml in a volumetric flask

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Calculate the weight of pectin to be used as 650 ÷ assumed grade — jellies must contain 65% TSS (650 g of TSS in 1000 g of jelly); example: for an assumed grade of 150, 4.33 g (650/150) of pectin is required

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Weigh 646 g of sugar and 4.33 g of pectin; mix the pectin thoroughly with about 20–30 g of weighed sugar in a dry beaker

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Note the tare weight of a 3-quart stainless steel saucepan and a stirrer; pour 410 ml of distilled water into the pan, followed by the sugar-pectin mixture

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Stir gently for about 2 min; place the saucepan on a stove or gas burner (if an electric heater is used, preheat it) and heat with stirring till the contents come to a full rolling boil

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Add the remaining sugar and continue heating and stirring until the sugar has dissolved; continue boiling until the net weight of jelly is 1015 g — if the net weight is less, add distilled water in slight excess and boil down to the correct weight; the entire heating time should not exceed 5–8 min

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Remove from the scale; allow the jelly to stand for 1 min, then slightly tip the pan on its side so the contents are nearly ready to overflow; skim off any foam or scum

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Remove the stirrer, place a thermometer in the pan, and stir gently with it until the temperature is exactly 95°C

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Pour the jelly quickly into three Ridgelimeter glasses, each containing 2 ml of tartaric acid solution; while pouring, stir vigorously with a glass rod — pour rapidly until the glasses are filled part way up the sideboard, then more slowly so each glass is filled completely full to the point of overflowing, so the acid solution mixes with the jelly

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Fifteen minutes after filling, cover the glasses with regular metal lids which fit snugly over the sideboards; store the jellies for 20–24 hr at 25 ± 3°C

Procedure — Measurement

At the end of the storage period, tear off the sideboard

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Slice off the exposed jelly with the tightly stretched wire, which must be clean and wet; while slicing, hold the glass upright and turn it slowly part way around so that a smooth cut is made; remove the detached layer and discard it

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To detach the jelly, hold the glass slightly tilted at an angle of about 45°, insert the tip of a spatula between the jelly and the glass wall to start separation, and slightly rotate the spatula if necessary

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Invert the glass carefully just above the square glass plate provided along with the instrument, so that the jelly slides down — do not drop the jelly

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Start the stopwatch as soon as the jelly is put on the glass; place the jelly and the plate carefully on the base of the Ridgelimeter so that the jelly is centered under the micrometer screw

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After exactly 2 min, bring the point of the micrometer screw just into contact with the jelly surface

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Read the sag to the nearest 0.1%: the lowest line on the vertical scale beyond which the lower edge of the circular micrometer head has passed is the per cent, and the number on the micrometer head nearest the vertical scale denotes the tenth of a per cent sag

Calculation

True Grade = Factor × Assumed Grade

Where,

• True Grade = true jelly grade of the pectin
• Factor = factor from Table 2-2 for the measured Ridgelimeter reading (% sag)
• Assumed Grade = actual weight of total soluble solids in the jelly divided by the weight of pectin used in that jelly; the pectin charge is set as 650 ÷ assumed grade so the jelly contains 65% TSS

A jelly sag of 23.5% is assumed as “standard firmness.” Test jellies which are 20% above or below standard firmness may be graded with accuracy. Example: assuming a jelly was made at 200 grade and showed 26.0% sag, the true grade is 0.9 of the assumed grade, or (200 × 0.9) = 180.

Note: the book’s procedure text defines “assumed grade” as the ratio of the actual weight of pectin to that of sugar in the jelly, while the Table 2-2 footnote defines it as the actual weight of total soluble solids divided by the weight of pectin; the footnote definition is the one consistent with the worked example (650/150 = 4.33 g). Carried as printed.

Table 2-2: Exchange Ridgelimeter Factors for the Standardization of Pectin

Multiply ‘Assumed Grade’ by Factor to get True Jelly Grade.

Values calculated by H. H. Holton and G. H. Joseph in January 1951 from the Ridgelimeter calibration curve illustrated in Fig. 2.9. “Assumed grade”: actual weight of total soluble solids in a particular jelly divided by the weight of pectin used in that jelly. Ridgelimeter factors must be applied only to the ‘assumed grade’ of the pectin in the particular jelly being examined. (Courtesy: Sunkist Research Department, U.S.A.)

Precautions

• When Ridgelimeter readings on different glasses from the same jelly batch differ by more than 0.6, remake the batch.
• Note the TSS with the help of a refractometer and apply temperature correction — a variation of ±1% from 65% at 20°C can mean an error of 3 to 4%.

References

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

Cox, R.E. & R.H. Higby, Food Ind., 16, 441 (1944) — cited in the book.

Joseph, G.H. & W.E. Baier, Food Technol. (Chicago), 3, 18 (1949) — cited in the book.

Lockwood, H.C. & R.S. Hayes, J. Soc. Chem. Ind., 50, 145T, April 24 (1931) — cited in the book.

I.F.T. Committee Report on Pectin Standardization, Food Technol., 13, 496 (1959) — cited in the book.