ISI 13-2e Determination of Starch in Tubers by Under Water Weight

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1. Scope	The method is applicable to potato and cassava. For cassava roots it is important to note that the results can easily be compromised by air taken up in the roots	LT 1986 Rev. LT 31. Dec. 1997 Rev. LT 18. March 2019
2. Principle	Determination of under water weight of 5050 g tuber & roots
3. Apparatus	3.1 Underhanging balance 3.2 Stainless steel rod with two hooks. Distance between hooks = height of basket + approx. 10 cm. 3.3 Weighing net basket in stainless steel 3.4 Vessel with clean water of maximum 18 oC
4. Procedure	Suspend rod (3.2) in underhanging balance (3.1). Place basket (3.3) on upper hook of rod (3.2). Place vessel (3.4) below balance, rod and basket. Fill vessel with water a few cm below basket.
TARA	Weigh TARA HIGH (To) of rod and empty basket to the nearest 0.1 g. Move basket to lower hook and weigh TARA LOW (Tu) to the nearest 0.1 g of rod and empty basket.	Adjust hooks so basket is completely immersed in water on lower hook.
Tubers	Weigh 5 kg clean tubers to the nearest 1 g (Wo) into basket (3.3) on upper hook.
	Move basket with sample to lower hook and weigh again (Wu) to the nearest 0.1 g	Completely immersed
5. Calculation	Calculate starch as starch dry matter of sample as is and report with one decimal.
Dry sample	Starch % = 5050 * 0.051738 ((Wu - Tu) / (Wo - To)) - 5.2463	Clean and dry tubers
Wet sample	Starch % = 5050 * 0.051738 ((Wu - Tu) / (0.98 (Wo - To))) - 5.2463	Correcting tuber weight 2% if wet
6. Notes	In stead of weighing 5050 g exactly and using a table as the official method the above version is generally accepted.
7. Reference	"Instruction no. 2 Mkt. 4410-4-96 of July 1996" issued by The Danish EU-directorate, Ministry of Agriculture & Fishery enforced 1st July 1996	EU-method
8. Image		The picture reproduces better when printed than on the web screen
		The EU-method is valid for potatoes within a range of 13-23 % starch dry matter. This range in this graph is extended to 35% starch dry matter by extrapolation. If the analytical method is used on cassava roots, the results can be compromised by air taken up in the roots.