I apologize for the necro-post, but for anyone who may be looking into this as I just was, I may have something of a solution.
Recently, I set up my own lil' cellar for the first time. First issue, was that it was too big. So, new cobblestone wall went in, brought it down to 6x6x4, rather than the larger size it has been. That notably brought down the ratio, but not by much.
Seeing how my cellar was below my home, and not subject to sunlight, I started experimentation. I placed a door at the bottom, and the top, sealed in the shaft with walls, leaving only the doorways, and the ladders down accessible. A negligible boost to the downtick rate on degradation of food items.
Then, for the heck of it, I removed one of the ladders at the top, and placed a dirt block on the hole in the ceiling connecting my cellar to my main living quarters. The rate of which food degraded absolutely PLUMMETED down to absolutely tiny numbers.
So, the solution may just be turning your cellar into an absolutely sealed environment, closing your accessway with an easily breakable block. That at the very least, was the solution that worked for me tonight.