The most important element in determining how much of a spice to use is to figure out who will be eating what you cook. Assuming you have followed a recipe once, you can get creative on your second go round. If you are eating alone, and you love a particular spice, go ahead and boost up the flavor. However, if you are new to spices or don’t want to use your friends as guinea pigs, then try a moderate increase of one-eighth teaspoon for every two servings.
When cooking for a group it is best to play the middle ground and try to please everyone. If children are involved remember that their taste buds are more acute than that of a forty-five year old, whose taste buds have started to diminish.
Also keep in mind that some spices in excess are not good for you, especially if you are pregnant. For example, file powder from sassafras trees can cause organ damage. You should be safe if you buy it in stores. However, the leaves are harmful in the wild. Other flavorings that may cause problems are licorice, monosodium glutamate, rue and sumac. Even such common herbs and spices as juniper, lovage and nutmeg should be used in moderation.
The potency of a flavoring can be influenced by whether you add it at the beginning or end of your cooking cycle. Some seasonings hold up better than others over time. For example, basil should be used sparingly, but if you put it in at the beginning of a slow cooking cycle, you can very well cook out the flavor. Thus, use less and add it at the end. Rosemary is another robust herb with a strong flavor that is best used in moderation. Most other herbs are more subtle in their flavor and can be used generously. But again, add them at the end of cooking. The most noted exception is the bay leaf, which reacts to heat and moisture, and, thereby, increases its flavor when thrown into a crock-pot or pressure cooker at the very beginning.
Sometimes cutting the leaves of an herb will release more of its flavor. So if you are in short supply, consider cutting them up before adding them to your meal. For spices, such as caraway or fennel seeds, the same thing holds true. By crushing the seeds, you can get more flavor. Dry roasting seeds, such as cardamom, can also bring out a spice’s intensity.
Another factor that can influence the strength of a spice is how it will be stored as a leftover. Have you ever spiced up your spaghetti sauce with some cayenne powder and noticed a stronger, acidic flavor when it was thawed? That is a good example of how freezing can influence flavor. That same defrosted spaghetti will need a little boost of Italian seasoning and a pinch or two of sugar to combat that acidic, peppery taste. Next time consider holding back on the cayenne at least on the leftover portion.
Keep in mind the type of food you are spicing. Does it readily absorb flavors, like potatoes or mushrooms? Does it have a natural sweetness, such as carrots that can handle a contrasting (mustard seed) or complementary (ginger) spice?
Getting adventurous with spices is all well and good, but knowing when to be aggressive and when to hold back is also important. Over time your knowledge will become instinctive, and you will develop a sense not only of what quantities to use, but the timing and best spice and herb combinations, as well.