CFR > Title 7 - Agriculture > SUBTITLE B—Regulations of the Department of Agriculture > CHAPTER I—AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing Practices), DEPARTMENT OF AGRICULTURE (parts 27 to 206) > SUBCHAPTER C—REGULATIONS AND STANDARDS UNDER THE AGRICULTURAL MARKETING ACT OF 1946 (parts 51 to 75) > PART 51—FRESH FRUITS, VEGETABLES AND OTHER PRODUCTS 1,2 (INSPECTION, CERTIFICATION, AND STANDARDS) > SUBPART —United States Standards for Grades of Potatoes for Processing 1 (§51.3410 to §51.3418) > 51.3417—Optional test for specific gravity.

51.3417—Optional test for specific gravity.

Tests to determine specific gravity shall be made in accordance with the procedures set forth in this section.
(a) The potatoes used for such determinations shall be:
(1) Taken at random from a composite sample drawn from containers representative of the lot.
(2) A comparable sample from a bulk load or storage bin.
(3) From a portion of the divided sample initially drawn or submitted for determination of grade or contract compliance.
(4) Representative of the lot with respect to size and quality.
The specific gravity for any lot of potatoes shall be the average of at least 3 corrected readings on separate tests from the composite sample. Specific gravity may also be determined, if requested, in accordance with size classifications or weighted value in proportion to size and/or grade separations in the lot.
(b) Specific gravity shall be determined by either;
(1) Calculation from the weights of the sample in air and in water made with USDA approved equipment. The reading obtained from each test shall be corrected for temperature variations using Table I.
(2) A hydrometer specifically designed for determining the specific gravity of potatoes. 3

Code of Federal Regulations

Footnote(s): 3 The hydrometer is available from the Potato Chip/Snack Food Association, Crystal Square-3, Suite 903, 1735 Jefferson Davis Highway, Arlington, VA 22202.

Code of Federal Regulations

The pulp temperature of the potatoes and the temperature of water shall be recorded immediately before testing and the specific gravity reading corrected using Table I.
Code of Federal Regulations 516
Table I—Correction Factors for Specific Gravity of Potatoes 4
[Corrected to zero at 50 °F potato temperature and 50 °F water temperature]
Water temperature (degrees Fahrenheit)
38° 40° 45° 50° 55° 60° 65° 70° 75° 80°
Potato temperature:
38° −0.0021 −0.0020 −0.0018 −0.0018 −0.0020 −0.0023 −0.0029 −0.0038 −0.0047 −0.0056
40° −.0017 −.0016 −.0014 −.0014 −.0016 −.0019 −.0025 −.0034 −.0043 −.0052
45° −.0009 −.0008 −.0008 −.0006 −.0008 −.0011 −.0017 −.0026 −.0035 −.0044
50° −.0003 −.0002 0000 0000 −.0002 −.0005 −.0011 −.0020 −.0029 −.0038
55° .0001 .0002 .0004 .0004 .0002 −.0001 −.0007 −.0016 −.0025 −.0034
60° .0004 .0005 .0007 .0007 .0005 .0002 −.0004 −.0013 −.0022 −.0031
65° .0005 .0006 .0008 .0008 .0006 .0003 −.0003 −.0012 −.0021 −.0030
70° .0006 .0007 .0009 .0009 .0007 .0004 −.0002 −.0011 −.0020 −.0029
75° .0007 .0008 .0010 .0010 .0008 .0005 −.0001 −.0010 −.0019 −.0028
80° .0008 .0009 .0011 .0011 .0009 .0006 0000 −.0009 −.0018 −.0027
85° .0009 .0010 .0012 .0012 .0010 .0007 .0001 −.0008 −.0017 −.0026
90° .0010 .0011 .0013 .0013 .0011 .0008 .0002 −.0007 −.0016 −.0025
95° .0011 .0012 .0014 .0014 .0012 .0009 .0003 −.0006 −.0015 −.0024
100° .0012 .0013 .0015 .0015 .0013 .0010 .0004 −.0005 −.0014 −.0023
4 To apply correction factor, change actual specific gravity reading by adding or subtracting the appropriate factor according to the plus or minus sign.
When requested to convert the weight in water of 5000 gram samples used in the weight in air versus weight in water method of specific gravity determinations, the conversion to total solids shall be based on Table II.
Table II—Specific Gravity Conversion Chart for 5,000 Grams of Potatoes
Water weight Specific gravity Total solids
300 1.0638 17.2
310 1.0661 17.7
320 1.0684 18.2
322 1.0688 18.3
324 1.0693 18.4
326 1.0697 18.5
328 1.0702 18.6
330 1.0707 18.7
332 1.0711 18.8
334 1.0716 18.9
336 1.0720 19.0
338 1.0725 19.1
340 1.0730 19.2
342 1.0734 19.3
344 1.0739 19.4
346 1.0743 19.5
348 1.0748 19.6
350 1.0753 19.7
352 1.0757 19.8
354 1.0762 19.9
356 1.0766 20.0
358 1.0771 20.1
360 1.0776 20.2
362 1.0780 20.3
364 1.0785 20.4
366 1.0790 20.5
368 1.0794 20.6
370 1.0799 20.7
372 1.0804 20.8
374 1.0808 20.9
376 1.0813 21.0
378 1.0818 21.1
380 1.0822 21.2
382 1.0827 21.3
384 1.0832 21.4
386 1.0836 21.5
388 1.0841 21.6
390 1.0846 21.7
392 1.0851 21.8
394 1.0855 21.9
396 1.0860 22.0
398 1.0865 22.1
400 1.0870 22.2
402 1.0874 22.3
404 1.0879 22.4
406 1.0884 22.5
408 1.0888 22.6
410 1.0893 22.7
412 1.0898 22.8
414 1.0903 22.9
416 1.0908 23.0
418 1.0912 23.1
420 1.0917 23.2
422 1.0922 23.4
424 1.0926 23.5
426 1.0931 23.6
428 1.0936 23.7
430 1.0941 23.8
432 1.0946 23.9
440 1.0965 24.4
450 1.0989 24.9
460 1.1013 25.4
470 1.1040 26.0
Whenever the recorded water weight for an individual reading falls between two sets of numbers as indicated in Table II, the next higher reading shall be used.