University of Idaho - I Banner

Visit UI

Learn about the many reasons the University of Idaho could be a perfect fit for you. Schedule Your Visit

Student Life

Fill your college experience with memories and connections that will define you as an individual and empower you for a lifetime. Explore

Parents on campus during orientation

Parent Newsletter

Keep up on campus events and information involving your Vandal student. Sign Up

UI Retirees Association

UIRA has a membership of nearly 500 from every part of the University. Join Today

PNW 664 • A PACIFIC NORTHWEST EXTENSION PUBLICATION

Making Garlic- and Herb-Infused Oils at Home

Barbara Abo, Josh Bevan, Surine Greenway, Beverly Healy, Sandra M. McCurdy, Joey Peutz, Grace Wittman

Infused oils

Introduction

Endless culinary possibilities exist for preparing and using herb- and garlic-infused oils at home. Herbs are easy to grow in home gardens or containers, providing an inexpensive and plentiful supply for infusion. Many ethnic cuisines are characterized by specific combinations of garlic and herbs that transform ordinary ingredients into culinary classics. Popular uses for infused oils include bread dipping, making salad dressings, and flavoring pastas.

Infusion involves immersing garlic, basil, oregano, or rosemary in oil to extract their flavors. Infused oils have the potential to cause botulism, however. Before getting too creative, make sure your infused oils are safe to eat by following the food safety guidelines in this publication. Our procedure for acidifying garlic and herbs will allow you to safely store your infused oils at room temperature. Refrigeration of the oils will maintain their fresh flavor for a longer time.


Botulism and flavored oils

A number of cases of botulism, a debilitating and potentially fatal form of food poisoning, have occurred as a result of improperly stored, home-prepared, garlic or herb-in-oil mixtures. Garlic and herbs can be a source of Clostridium botulinum, widespread bacteria that produce the botulism toxin under certain conditions. When garlic or herbs are placed in oil, the low-acid, oxygen-free environment favors the growth of these bacteria.

Commercially available oils flavored with garlic and herbs either have been acidified to prevent the growth of bacteria or they contain specific levels of microbial inhibitors. When purchasing from boutique or small-scale producers, check the label or ask the producer to ensure this required safety treatment has been applied.

Procedures for preparing garlic- and herb-flavored oils at home without acidifying the flavoring materials are available, but the food safety control for these products is refrigeration for a maximum of 2–4 days or freezing. It is unsafe to store these home-prepared garlic or herb-infused oils at room temperature.

The acidification procedure described in this publication was based on research conducted at the University of Idaho and reported in Food Protection Trends, https://www.foodprotection.org/publications/food-protection-trends/. The research identified the conditions necessary to prevent growth of the botulism bacteria when garlic and herbs are immersed in oil. Refrigeration of these infused oils is recommended for quality, but not required for safety.


Procedure

Acidification of garlic and herbs

Raw, chopped garlic or fresh herbs (basil, oregano, or rosemary) are immersed in a 3% solution of citric acid. After soaking for 24 hours, the acid is drained away and the acidified garlic or herbs are ready for addition to your vegetable oil of choice.

Citric acid. Citric acid imparts less flavor than lemon juice or vinegar. It is often available at health food stores, pharmacies, grocery stores, and other retail outlets that carry canning supplies (Figure 1). The price varies (from $0.50 to $4.51/oz in a 2011 Idaho survey), so you may want to shop around. Lemon juice and vinegar have not been tested for acidifying the garlic and herbs for making infused oils and cannot be substituted for citric acid. It is important not to confuse citric acid with ascorbic acid (vitamin C); ascorbic acid does not have the same acidifying properties as citric acid.

Citric acid
Figure 1. Use citric acid to acidify garlic and herbs.

Garlic and herbs. The acidification procedure was developed for garlic, basil, oregano, and rosemary. Do not use it with other vegetables or herbs until the appropriate research has been conducted.

Soaking. The garlic or herbs are soaked in 3% citric acid at room temperature for 24 hours to allow the acid to fully penetrate the ingredients and bring the acidity beyond the growth limit for the botulism bacteria. Less concentrated acid solutions or shorter soaking times can result in an unsafe product.

For garlic, the soaking ratio is 1 part garlic to 3 parts 3% citric acid solution, by weight (Table 1). This is equivalent to ⅔ cup coarsely chopped, peeled garlic cloves to 2 cups of citric acid solution. Garlic cloves must be peeled and coarsely chopped prior to soaking, with pieces no larger than ¼ in in any direction to allow complete penetration by citric acid.

Table 1. Soaking ratios for acidifying garlic and herbs in a 3% citric acid solution.
Flavoring material Soaking ratio by weight Soaking ratio by volume
Garlic 1 part garlic to 3 parts 3% citric acid solution ⅔ cup coarsely chopped garlic cloves to 2 cups citric acid solution
Herbs 1 part fresh herbs (leaves still attached to stems) to 10 parts 3% citric acid solution 1½ cups (1.7 oz) loosely packed herbs (leaves still attached to stems) to 2 cups citric acid solution

The soaking ratio for the three herbs (basil, oregano, rosemary) is one part of fresh herbs (stems with leaves attached) to 10 parts of 3% citric acid solution, by weight (Table 1). This is roughly equivalent to 1½ cups of loosely packed herbs to 2 cups of citric acid solution, but it is best to weigh out 1.7 oz (47 gm) of herbs. Weighing the herbs is more accurate than using a volume measure because the density of fresh herbs can be quite variable. During soaking, a weight should be placed on the herbs to keep them under the soak solution for the full 24 hours (Figure 2).

Submerge herbs
Figure 2. Weigh down the herbs to keep them completely submerged in citric acid solution.

Infusion

After the garlic, basil, oregano, or rosemary has been acidified, it can be used to impart flavor to oil. Consider the type of oil and the time and temperature of infusion.

Oils. Olive oils often are infused with flavoring materials. Garlic and herbs offer a nice complement to olive oil’s distinct flavor. If you are interested in having the garlic or herb flavor predominate, consider using a blander oil, such as canola oil. Canola and olive oils are nice because they contain fewer polyunsaturated fatty acids than many other vegetable oils and thus oxidize and become rancid less quickly.

Infusion ratio, time, and temperature. The proportion of flavoring material to oil and the temperature of the infusion affect how quickly the flavoring material will infuse into the oil. Experiment to determine the conditions that produce a flavored oil most suited to your taste. The ratio of flavoring material to oil used in our research was 1 part acidified garlic or herb to 10 parts oil, but the ratio may be increased or decreased to suit personal tastes.

Successful infusions were conducted at room temperature (about 70°F) for 1–10 days, with the intensity of the infused flavor increasing over time. Oils may also be heated to more quickly infuse the flavoring materials. Our research successfully used acidified herbs to flavor oil at an infusion temperature of 140°F for 5 min. Significantly hotter temperatures would damage oil flavor.

Because flavors will continue to intensify with time, it is best to remove the acidified garlic or herb from the oil when it has reached the desired flavor. However, it is acceptable to leave the garlic or herb in the oil, particularly rosemary, for an attractive look, a practice sometimes used with commercially flavored oils.


Storage of infused oils

While oils infused with flavors from acidified garlic, basil, oregano, and rosemary can be safely stored at room temperature, oil flavor quality is maintained for a longer period of time with refrigerator or freezer storage. It is also best to protect infused oils from light by storing them in dark-colored bottles. Make sure the bottles are clean and food grade. All vegetable oils retain quality better at cold temperatures and when protected from light.


Q & A

Do I have to acidify the garlic and herbs that I want to use for infusing oils?

Yes. If you want to infuse or store the oil at room temperature, you must acidify the garlic or herbs to avoid potentially deadly toxin production of Clostridium botulinum, the bacterium that causes botulism. If you mix oil with raw garlic or herbs that have not been acidified, refrigerate the mixture and use it within four days or freeze it for long-term storage.

How do I can my infused oil?

There are no recommended procedures for canning flavored oils. If you follow the procedures described here, canning is not necessary.

Can I use the recipe for acidifying garlic, basil, oregano, and rosemary with other materials such as peppers, mushrooms, or other herbs?

No. Research to determine acidification procedures for ingredients other than garlic, basil, oregano, and rosemary has not been conducted at this point.

Can dried garlic or herbs be used to flavor oils?

If you season oil with dried garlic, dried herbs, or both, you must refrigerate the mixture and use it within four days or freeze it for long-term storage.

In theory, dried garlic and herbs cannot support the growth of bacteria because they contain too little moisture. However, without specialized laboratory equipment, it is not possible to determine if the garlic and herbs are truly dry enough. Even a very small pocket with sufficient moisture can allow bacteria to grow and produce toxin.

Whole garlic is more attractive than chopped garlic when left in my garlic-infused oil. Can I use whole garlic instead of chopped?

No. Whole garlic acidifies much more slowly than chopped garlic and does not reach the required level of acidity within 24 hours.

Can I acidify two herbs at the same time; for example, use ¾ cup each of basil and rosemary in 2 cups of 3% citric acid?

Yes. The herbs tested so far (basil, oregano, and rosemary) can be acidified together as long as you use the correct ratio of total herbs to acid solution. Garlic must be acidified separately because the ratio of garlic to acid solution is different.

It is OK to leave the garlic or herbs in the acid solution for longer than 24 hours?

Soaking the garlic or herbs a few hours longer than 24 is fine, but leaving them in the acid longer will result in a less desirable appearance and flavor.

Can I use any mixture of garlic and herbs to flavor the oil?

As long as you acidify the garlic, basil, oregano, and rosemary according to the instructions provided here, you can use them in any combination to produce flavor-infused oil.


Acidified garlic for oil infusions

  • 2 cups water
  • 1 Tbsp citric acid
  • about 8 oz garlic bulbs

To make the 3% citric acid solution, pour 2 cups warm water into a mixing bowl. Add 1 level tablespoon of granular citric acid and stir gently, dissolving the citric acid completely.

Separate the garlic bulbs into cloves and peel garlic cloves. Chop the peeled garlic into pieces about ¼ in square and no larger.

Place ⅔ cup chopped garlic into the acid solution and stir gently. Cover and hold at room temperature for 24 hours to allow garlic to become fully acidified.

After 24 hours, remove the acidified garlic from the solution; drain well.

Add the acidified garlic to your choice of oil and allow its flavor to infuse the oil to taste. Start with 1 part garlic to 10 parts oil, by weight; add more garlic to taste if you wish.

Acidified herbs for oil infusions

  • 2 cups water
  • 1 Tbsp citric acid
  • 1½ cups (47 gm or 1.7 oz) fresh rosemary, basil, or oregano, loosely packed, leaves attached to stems

To make the 3% citric acid solution, pour 2 cups warm water into a mixing bowl. Add 1 level tablespoon of granular citric acid and stir gently, dissolving the citric acid completely.

Rinse the fresh herb and pat dry.

Place 1½ cups of herb into the acid solution. Make sure the acid solution completely covers the herb. Use a clean dish to weigh down the herb and keep it submerged. Cover the bowl, and allow the herb to soak up the acid solution for at least 24 hours.

After 24 hours, remove the herb from the solution, drain well, and gently pat dry.

The herb is now safe to place in an oil of your choice.

Additional useful information

Kendall, P., and J. Rausch. 2012. Flavored Vinegars and Oils. Fact Sheet no. 9.340. Colorado State University Extension. Available at https://extension.colostate.edu/topic-areas/nutrition-food-safety-health/flavored-vinegars-and-oils-9-340/.

Raab, C. and M. Woodburn. 2015 (revised). Food Safety and Preservation: Herbs and Vegetables in Oil. SP 50-701. Oregon State University Extension Service. Available at https://extension.oregonstate.edu/sites/default/files/documents/8836/sp50701herbsandvegetablesinoil.pdf.

Simmone, A. 2013. Herbs and Garlic-in-Oil Mixtures: Safe Handling Practices for Consumers. FCS8743, University of Florida Extension. Available at http://edis.ifas.ufl.edu/pdffiles/FY/FY48700.pdf. (out of print)


About the Authors

Barbara Abo—Extension Educator, University of Idaho Extension, Ada County

Josh Bevan—Director, University of Idaho Food Technology Center, Caldwell

Surine Greenway—Extension Educator, University of Idaho Extension, Owyhee County

Beverly Healy—former Extension Educator, University of Idaho Extension

Sandra M. McCurdy—former Extension Food Safety Specialist, University of Idaho Extension

Joey Peutz—Extension Educator, University of Idaho Extension, Payette County

Grace Wittman—Extension Educator, University of Idaho Extension, Cassia County



Note: The procedure in this publication is based on work reported in the following journal article: B. Abo, J. Bevan, S. Greenway, B. Healy, S. M. McCurdy, J. Peutz, and G. Wittman. 2014. Acidification of Garlic and Herbs for Consumer Preparation of Infused Oils. Food Protection Trends 34(4): 247–57.

Pacific Northwest Extension Publications

Pacific Northwest Extension publications are produced cooperatively by the three Pacific Northwest land-grant universities: Washington State University, Oregon State University, and the University of Idaho. Similar crops, climate, and topography create a natural geographic unit that crosses state lines. Since 1949, the PNW program has published more than 700 titles, preventing duplication of effort, broadening the availability of faculty specialists, and substantially reducing costs for the participating states.

Pacific Northwest Extension publications contain material written and produced for public distribution. You may reprint written material, provided you do not use it to endorse a commercial product. Please reference by title and credit Pacific Northwest Extension publications.

Order Information

University of Idaho Extension

http://www.uidaho.edu/extension/publications
208-885-7982 | 208-885-9046 (fax) | calspubs@uidaho.edu

Washington State University Extension

https://pubs.extension.wsu.edu
800-723-1763 | 509-335-3006 (fax) | ext.pubs@wsu.edu

Oregon State University Extension Service

https://catalog.extension.oregonstate.edu
800-561-6719 | 541-737-0817 (fax) | puborders@oregonstate.edu


Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Barbara Petty, Director of University of Idaho Extension, University of Idaho, Moscow, Idaho 83844. The University of Idaho has a policy of nondiscrimination on the basis of race, color, religion, national origin, sex, sexual orientation, gender identity/expression, age, disability or status as a Vietnam-era veteran.

University of Idaho Extension

 

Physical Address:
E. J. Iddings Agricultural Science Laboratory, Room 10
606 S Rayburn St

Mailing Address:
875 Perimeter Drive MS 2332
Moscow, ID 83844-2332

Phone: 208-885-7982

Fax: 208-885-9046

Email: calspubs@uidaho.edu

Location

Barbara Petty

Email: extdir@uidaho.edu