This guide explains how do you stockpile food for winter when it decays so fast.
Guide to Stockpile Food for Winter
In the Early Game
There is no point in having more that about 2 days worth of food on hand, because it will spoil before you can eat it.
How to Preserving Food
There are two approaches to preserving food:
First is tech advancement
If you can get iron bars, you can make a meat smoker, which will cause meat (and later fish) to last much longer. If you can get to iron nails, you can build a mushroom drying rack; dried mushrooms last forever if kept dry. If you can build a kitchen (also requires nails), you unlock the quern / dough bench / bread oven, which lets you eat oats. Oats last forever in their raw state, making them an excellent food to stockpile.
Second is lateral thinking
If you dig into a mountain and put in a door to make a small cave, it will be colder than the outside world. So even in summer you can keep your food in a cave to preserve it a bit. However, towards the end of fall it will get below freezing in a cave at night, so if you put a whole bunch of jugs of water in your cave, they will freeze, and the ice will keep the cave below freezing until winter time, letting you stock up on mushrooms and eels while they’re still available.
Also note that you can buy food from traders, and they stop by pretty frequently even in winter if you maintain good relations.