Hi @Tyron,
It appears that after the 18.5 update, the cellar bonus is no longer functioning correctly regarding food spoilage. The modifier on the food "appears" to be correct, but if you pick up a food item in a cellar and immediately put it back down, it fast forwards the spoilage point quite far ahead.
I can very easily repro this in creative:
1. Create a 3x3 cellar
2. Grab an apple pie from the creative menu (default life span 8 days)
3. Put it on the cellar floor and note the spoilage bonus (in my case, the spoilage modifier was 0.27)
4. Note that the Pie now says it should last ~28 days (as expected)
5. Simulate time passing (I used /time add 4 days)
6. Note that the pie now says it has 24 days remaining (as expected)
7. Pick up the pie and immediately put it down
8. The pie now says it only has 14 days remaining (!!!)
I noticed something was wrong while playing my survival world (I was taking food off my shelf and it was immediately turning to rot in my hands). Honestly, a bit surprised that no one else has mentioned this yet.