Buying food, especially dry goods or other products with fairly long shelf lives, in bulk is a good way to cut back on your grocery bill. You get a lower overall price per pound or per ounce. The only problem with buying in bulk is that whatever you buy has to be stored properly to give it its optimal shelf life and to prevent spoilage. Basic pantry ingredients are great choices for bulk buying because you always want to have them on hand. You just need to choose foods that can last for a long time, rather than something that needs to be used up very quickly.
Flour is a pantry staple that anyone who bakes (and most people who cook) will want to have, and although it can have a long shelf life, it also needs special care. Flour should be kept in an airtight and moisture-tight container set up off the floor. The typical flour bag size is 5lbs, and bulk bags generally run up to 25-40 pounds. If you choose a very large container, it should be large enough to hold the bag without having to pour the flour out (keeps things cleaner, generally) and should be relatively easy to open/close when you need to use the flour.
All purpose flour, as well as cake flour and other “white” flours, can keep for 6-12 months in good storage conditions. Whole wheat flour should not be kept as long, since it contains more of the grain of the wheat and has a much higher spoilage rate (it can turn rancid and taste off after a while) than all purpose flour. Flour should be kept in a cool environment, as the grain can spoil. It does not need to be kept in the freezer, although the freezer temperature can prevent spoilage from taking place or insects from getting to the grain. It is very important to use an airtight container in the freezer, as humidity from a refrigeration unit can adversely effect the flour. Your storage containers should also be kept out of the sunlight, in a dark or dim place.
Some flour storage containers are built to exactly fit the flour bag. Others are smaller and require you to pour the flour out of its original bag, but work well if you use the flour regularly and don’t want to pull it out of a larger storage container. If you buy in bigger bags, a restaurant-type storage container can actually work very well at home, although there are smaller bins that will hold up to 25-lb bags, too. If you just want to keep that large bag in something airtight, a giant ziplock bag will do the trick, as well.