If you don't do much baking, or you haven't baked in a while, you might be wondering if those baking supplies in your cupboard are still good. Below we list the basic baking ingredients and how to tell if they're still OK to use.
These guidelines assume your pantry stays below 85 F. Storing ingredients directly above or beside your oven will shorten their shelf lives, as will a humid climate.
First, the Good News
Let's start with two ingredients that don't go bad: sugar and salt. Sugar can form clumps, but you can easily break them up. Apart from that, sugar or salt won't spoil or alter their properties over time. Effectively, they last forever.
With its high alcohol content, pure vanilla extract likewise has an effectively infinite shelf life. (Imitation vanilla extract, on the other hand, as well as other flavored extracts like lemon or peppermint, will keep for six months to a year.)
Flour is the primary ingredient in baking, and the one most likely to affect the flavor of your baked goods if it goes bad.
Flour spoils mainly through rancidity, and to a lesser extent, mold and insect infestation. Rancidity is a chemical change in a fat that's exposed to oxygen, heat and light. You'll likely notice the sour smell of rancid flour right away. If so, toss it. Eating rancid flour isn't bad for you, but it'll taste and smell terrible.
Refined wheat flour (such as all-purpose flour) can last for 1 to 2 years if stored in an airtight container in a reasonably cool (up to 85 F), dry place. If you simply store the open bag in the cupboard with the top folded over, its shelf-life is more like 7 to 8 months.
Whole grain flours go rancid much more rapidly than refined flours. Its shelf-life is 2 to 3 months at room temperature, and up to six months in the freezer.
If you see insect eggs, larvae, or anything that crawls or has wings in your flour, toss it. The same goes for mold, which might resemble colored streaks similar to what you've seen on cheese.
Otherwise, flour doesn't harbor bacteria that cause food poisoning or food spoilage (and the oven's heat during baking would kill them anyway).
The leavening agents in your pantry are biological (i.e. yeast) or chemical (i.e. baking powder and baking soda). These don't spoil in the ordinary sense, but their effectiveness decreases if they get too old.
Yeast is a living organism. It eats sugar and produces gas, and this gas is what causes your bread to rise.
Yeast goes bad by dying, which renders it ineffective. And the yeast in a package don't all die at once, so its potency diminishes over time.
You can store unopened dry yeast at room temperature, but the fridge will extend their life. Once opened, store yeast in the fridge, where it will last for around four months, or in the freezer where it will last for six months.
Chemical leavening agents like baking powder and baking soda (they're not the same thing!) work by producing gas through a chemical reaction when combined with other ingredients. The compound that produces the reaction loses its potency over time, mainly through exposure to air, moisture and temperature.
To ensure full potency, replace these ingredients every six months. Like yeast, their diminshed effectiveness will be gradual: Year-old baking powder might still produce some rise, but not as much as it should.
Oils and Fats
As mentioned above, oils and fats spoil by becoming rancid, and this applies to cooking oils and solid shortening as well. Assuming you store them in a cool, dry, dark place, vegetable shortening (like Crisco) will keep for up to two years if unopened. Opened, a can of shortening will keep for a year (or six months for shortening sticks).
Liquid oil shelf lives vary by type and how refined they are, and they deteriorate more rapidly once they're opened. Refined oils overall last longer. Some oils, like grapeseed or walnut, might only last a few months once opened. But as a general rule, a bottle of cooking oil will last for a year on average (or twice that if refrigerated).