The spoilage index is an accumulation of the reciprocal of Safe Days. Safe Days depends on the temperature, T , and moisture content, MC. Safe days is defined as:
Number of days until germination capacity is reduced to 95% (Fraser & Muir 1981)
Safe Days = 10^(6.234 -0.2118 MC – 0.0527 T) wheat and cereals
= 10^(6.224 – 0.302 MC – 0.069 T) canola and oilseeds
The objective for safe storage, is to maximize the number of safe days by lowering the temperature T, and the moisture content, MC. Look at how the number of safe days varies with temperature for ‘dry’ wheat:
• 14.5% @ 30⁰C = 38 safe days
• 14.5% @ 20⁰C = 128 safe days
• 14.5% @ 0⁰C = 1458 safe days
• New Definition: Spoilage Index = Ʃ ( 1/ safe days) x 100
Example, if safe days is six, then after 3 days we will have an accumulated deterioration of: (1/6 + 1/6 + 1/6) x 100 = 50%, after 6 days : (6 x 1/6) x 100 = 100% of the way to 95% germination.
We modified the spoilage index in order to accumulate every hour instead of every day:
Spoilage Index (SI) = Ʃ ( 1/ safe days)/24 x 100
What we got from our trial runs from 2007 to 2015:
File SI trial time (hours)
071 22.6 214
072 13.7 259
073 11.6 14.8
0809P 3.1 54
0809W 23.8 290
0810B 60.6 291
0810W 24.9 215
0909B 3.6 151
0909W 149.8 268
1010 250 674
1110 71.6 239
1216 85.3 263 bin had no temp cables, so used discharge T
1217 364.6 335 used discharge T, so SI is questionable
1218 45 417 used discharge T
1219 85.3 405 used discharge T
1309B 3494 1274 certainly had spoilage here, cause high MC
1316 216.9 1724
1317 371.4 1910
1318 72.6 1741
1319 38.7 951
1409 1284 2020
1410 350 1296
1416 315.7 1969
1417 86.5 1969
1418 51.2 1600
1419 109.7 1600
1509 426.7 1940 but using sample tube MC 14.5% gives SI of 72.7
1510 104 1862 15.1 110.2
1516 242 1941 15.8 145
1517 276 1941 16.2 196
1518 399 2069 15.8 267.5
1519 397 1941 15.3 113.2
As you can see many of our trials had an SI > 100 and this was mainly due to starting with a high or very high MC so the SI grew quickly in the first few days.