Oil flavored with herbs can be safetly and economically made at home if sound instructions are followed exactly. The following safe guidelines established by USDA can help you evaluate flavored oil recipes you encounter.
Low acid foods such as herbs, mushrooms, peppers and garlic can support the growth of bacteria such as Clostridium botulinum which grows without air (oil makes anaerobic conditions) and produces toxin at room temperature. When consumed, such an oil would cause severe illness. Commercial flavored oils are acidified so can be stored at room temperature, unfortunately a safe recommendation for acidifying home made flavored oils has not been researched. Therefore, householders must alter the conditions of their oil so bacteria cannot grow. Lowering the temperature so bacteria cannot grow, or using dried herbs which lack the moisture to support bacteria growth are ways householders can keep their flavored oils safe.
When vegetables or herbs are immediately removed after flavoring the oil, the bacteria will not have a "food source" for growth. This strained flavored oil can be stored safely at room temperature, but will become rancid after several months. Rancidity is detected by off odors and off flavors. Rancidity is primarily a quality change, but there are safety concerns when rancid foods are routinely consumed over a long period of time. The rancidity problem makes it difficult to make flavored oils in the summer when herbs are abundant and economical to give as December holiday gifts. Many gift givers simply purchase herbs in winter and give freshly made oils.
When vegetables or herbs are dried, there is not enough moisture to support pathogen growth, so dried vegetables or dried herbs in oil can be stored safely at room temperature. However, the flavor of oils made with dried herbs and garlic is different from oils made with fresh, so making a small batch to see if the flavor is acceptable to you is advised.
Some people want their flavored oils to be the pretty bottles with lush green herbs and red peppers setting on the kitchen counter similar to the flavored vinegar bottles. This CANNOT be done safely. Flavored vinegars contain so much acid, that bacteria do not grow in them so flavored vinegars do not have to be refrigerated.
When raw or cooked vegetables or herbs are stored in oil, these mixtures must be refrigerated to slow bacterial growth. After 3 weeks refrigeration, the increased number of bacteria will become a food safety hazard; so that is the maximum storage time.
Return to Flavored Oil MenuFlavored oils can be safely stored in the freezer, but some herbs become limp, black objects when frozen. Freezing will delay the oil from becoming rancid for 4 to 6 months. Some people have had success freezing strained flavored oils. You may wish to try a small batch and see if the texture is acceptable to you.
Dried herbs, dried garlic, or dried tomatoes can be used to flavor oils without safety concerns because there is not enough moisture available for bacteria growth. However, if you add a combination of fresh and dried items to the oil, it must be refrigerated.
Return to Flavored Oil MenuTraditionally this recipe was made in climates where drying outside was practical--hence the name. The tomatoes can be either dried in the sun or in a dehydrator or oven. Solid-type tomatoes, such as Italian, dry well as they have a higher flesh to liquid ratio.
Under-dry tomatoes can be a safety hazard because they contain enough moisture for bacteria to grow. If you are not experienced in drying end points of tomatoes, check a drying book with photos. Your local Cooperative Extension office may carry such a publication for under $2.00. Or read How to Dry Foods by Deanna DeLong which is a good source of valuable advice and is carried by most public libraries or can be purchased inexpensively in paperback.
Remove stem and core of tomatoes. Halve, quarter or slice depending on shape you desire. If you halve or quarter, remove the seeds and watery pulp to speed drying. Sprinkle the tomatoes with a seasoned salt. Use small amounts because it will concentrate as the tomato dries. (Homemade seasoning: 1 Tb Italian seasoning, 2 tsp salt, 1/4 tsp garlic powder)
If drying in a food dehydrator, dry at 140F. AFter 4-5 hours, turn the tomatoes and press them flat if using quarters or halves. After a few hours, turn again and continue drying until very dry but still pliable (not crisp). This will take about 8 hours. If drying in an oven, use 170F, leave door adjar so moisture can escape, turn and flatten every 2-3 hours. May take 12 hours to dry.
The dried tomatoes can be packaged and frozen (you don't need to worry about moisture and color changes are greatly slowed), packaged and stored in a cupboard, or stored in oil. If storing dried foods in your cupboard, check a drying book with photos to be sure you have dried the foods properly.
To pack in oil, place throughly dried tomatoes (under-dry is a safety hazard) in a pint or half-pint jar. Cover with olive oil (or other oil). You may need to add more oil as the tomatoes are removed to keep them immersed. They will keep for months at cool room temperatures or in refrigerator.