| 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. |