Spoilage depends on how long the product stays at which temperature. Bacteria grow fastest between 4 and 60 °C; USDA FSIS notes that in this range their numbers can double in as little as 20 minutes, and says perishable food should not stay out of refrigeration for more than 2 hours, or 1 hour when the air is above 32 °C.
In a cold chain this means a two-degree excursion lasting ten minutes is not the same event as one lasting six hours. The effect is growth rate multiplied by time, so on a chart look less at the highest point and more at the area above the threshold line. Three hours at 8 °C gives bacteria more opportunity than a ten-minute spike to 12 °C.
Cold chain basics mean reading time and temperature together rather than as separate limits.
Frozen food is held to a tighter measure. Turkish Food Codex communiqué 2014/47 requires quick-frozen food to be kept at -18 °C or colder at every point in the product, allowing only brief rises of no more than 3 °C in transport. Beyond that, partial thawing lets ice crystals grow, and when the product refreezes its texture does not return.
How real is the spike on the logger
A logger usually measures the air in the body. When the door opens, that air warms within seconds and the chart shows a sharp spike, while the core of a large mass of product barely moves. A long, low plateau is easy to overlook, yet it genuinely warms the product. The record states what the sensor reads, and the decision follows the product temperature.
Interval logging also rounds the duration. With a logger reading every ten minutes, if 10:00 is in range, 10:10 and 10:20 are above the threshold and 10:30 is back in range, the excursion began between 10:00 and 10:10 and ended between 10:20 and 10:30, so it lasted between 10 and 30 minutes.
