Cooks extract the characteristic aroma chemicals of fruits and vegetables, herbs and spices, into a variety of liquids that then serve as convenient ready-made flavorings for sauces, dressings, and other preparations. In general, the freshest-tasting extracts come from slowly steeping intact raw fruits or herbs at room or refrigerator temperature for days or weeks. The flavors of dried herbs and spices are less altered by heat, and can be extracted more rapidly in hot liquids.
The growth of microbes that cause spoilage or illness is inhibited by the acidity of vinegar, the concentrated sugar in syrups, and the alcohol in vodka (whose own neutral flavor makes it a good medium for flavor extraction), so flavored vinegars, syrups, and alcohols are relatively trouble-free preparations. However, flavored oils require special care. The air-free environment within the oil can encourage the growth of botulism bacteria, which live in the soil, are found on most field-grown foods, and have spores that survive ordinary cooking temperatures. Cold temperatures inhibit their growth. Uncooked oils flavored with garlic or herbs are safest when made in the refrigerator, and both uncooked and cooked flavored oils should be stored in the refrigerator.