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Basic Guidelines
 in making
 OIL INFUSIONS
(12/09)

by Ken Atherton

Index
Introduction
Definitions

Choosing the Oil or Fat Menstruum

Preparing the Plant Material

Optimising and Standardizing Oil Infusions

Containers

Batch Record Book

Dry Weight Measurements of Herb

Preserving Oil Infusions

Oil Infusion Manufacturing Procedure

Separating the Oil from the Herb Material

Establishing an Expiry Date.

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Introduction

Oil and fat infusions (hence forth referred to as oil infusions) are a simple and effective means of extracting oil soluble components from herbal material. It is a common practice in food preparation where savoury herbs are used in making salad dressings. The infusion of medicinal herbs with fats and oils is a similar process. 

The medicinal efficacy of an oil infusion is a function of the quality and type of oil (the menstruum), the quality and concentration of the herbal material and the process used in the extraction.

Whilst savoury herb oil infusions are consumed as foods, most medicinal herb oil infusions are used topically.

Below is a basic introduction to the process of making medicinal herb oil infusions. Much of the information shared stems from experience gained working with the herbs fresh from the gardens at Pindari Herb Farm. Provided are practical guidelines for the "capturing" of the oil soluble components from plant material. There is limited detail on the medical properties, the parts of the plant used, and the time of harvest, this information being best sourced elsewhere.

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Definitions of commonly used terms in processing of Medicinal Herbs.

Comminution: The process of reducing the size of herb particles usually by grinding or cutting.
Decoction:
Extraction of herb by simmering (gently boiling,) usually in water.
Diminution: To make smaller, to cut into pieces.
Expression: Is the process of forcibly separating liquids from solids.
Exhaustion of herb material: Extraction of most or as much as possible from the plant material.
Glycetract: A tincture based on glycerin.
Fluid extract: A concentrated aqueous and alcohol extract of herbal material of strength usually 1:1 or 1:2 (dry weight to menstruum)
Fresh plant tincture: A tincture made from freshly harvested plant material
Infusion (aqueous): An extraction of water soluble components through the soaking in either hot or cold water. A "cup of tea."
Infusion (oil): An extraction of oil soluble components through the soaking in a vegetable or mineral oil or liquefied wax. A "salad dressing."
Maceration: The soaking of plant material in a menstruum.
Marc: The plant material remaining after the extraction of the soluble components.
Menstruum: A defined solvent or mix of solvents.
Oil Infusion: An extraction of oil soluble components through the soaking of plant material in an oil or fat.
Percolation: An extraction of soluble components via the passage of a menstruum through a column of plant material. e.g. "coffee percolation."
Proof spirit: An alcoholic mixture of standard strength. - In Australia and Britain 57.1% alcohol by volume is 100 proof spirit whilst in the US it is 50% alcohol.
Succus: The juice of fresh plant material usually preserved with ethanol. e.g. Cleavers succus.
Tincture: Usually an alcohol/aqueous solution obtained by the maceration of a herb with that solution. Usually 1:5 (dry weight to menstruum) or 1: 10 for more potent herbs such as Lobelia inflata.
Virgin oils: Oils that have not lost their "virgin" quality through processing and refining.

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Choosing the oil or fat menstruum

The nature of the menstruum chosen when making a herbal infusion, whether it is water, alcohol, a mix of both, glycerin or an oil or fat, will determine the material components that are extracted. This being dependent on the solubility of those components in the chosen menstruum and the ability of that menstruum to extract that component from the plant material.

A brief outline of some oil and fat menstruums are:

Lard - a saturated animal fat prepared from the internal fat of the hog abdomen.
Coconut oil - the saturated oil from the coconut which is the seed of the coconut palm.
Jojoba oil - a natural saturated fluid wax extracted from the Jojoba seed.
Olive oil - a mono unsaturated oil (high in omega 9 fatty acids).
Almond oil - an oil high in omega 9 with some omega 6 fatty acids.
Grape seed oil - an oil high in omega 6 with a little omega 9 fatty acids
Sunflower oil - an oil similar to grape seed oil.
Flax seed oil - an oil high in omega 3 with a little omega 6 and 9 fatty acids.

Some oil and fat menstruums have medicinal properties of their own that can be utilised as an adjunct to the healing properties of the infused herb. Thus the intended application of the infusion will influence the type of oil or fat chosen.

Saturated fats and oils are relatively stable to heat and light and were used in the past. But now cosmetically more acceptable and readily available vegetable oils such as Olive and Almond are mostly used.

With unsaturated oils, the more omega 6 and especially omega 3 fatty acids in an oil, the greater the chemical instability of the oil and the need for it to be used fresh and for it to be stored away from light, oxygen and heat. Antioxidants can be added to extend the "shelf life" of the oil and thus the finished product.

When purchasing an oil, choose only virgin cold pressed oils and select the longest dated product available. If purchasing in bulk, go direct to the producer of the expressed oil and obtain the date of expression, the method and temperatures used in the process and the storage history of the oil. Only by doing this can you be reasonably assured of "the nature" of the oil you have acquired.

Summary of factors affecting the choice of menstruum:

Olive oil is the menstruum of choice for many oil infusions because of its more stable mono-unsaturated chemical structure that gives it greater stability at room temperatures, compared with oils such as Almond and especially Flax seed. Jojoba oil is increasing in popularity but its use is limited by its higher cost.

A few people are allergic to nuts and nut oils including their use topically.

When making infusions from saturated  fats and oils such as Lard and Coconut it should be remembered that for an adequate infusion to occur, the menstruum needs to be in a liquid state.

In western societies there is an imbalance in the oil consumption in our diets with a general need to increase the level of omega 6 and especially omega 3 fatty acids. The quantities and the quality of these dietary oils can profoundly affect our health negatively and positively, similarly the topical application of these fats and oils also affect the health of the skin.

For a comprehensive understanding of the complex issue of fats and oils and our health, the following book is recommended: 
"Fats that Heal, Fats that Kill" written by Udo Erasmus and published by Alive Books. (ISBN 0-920470-38-6)

Harvesting and Preparing the Plant Material

After harvesting, foreign matter should be removed by hand. With insect life that is usually present in fresh flowers, place the picked herb in a cool shaded place for an hour or two and allow the bugs to crawl and fly away, or remove them manually.

With commercially obtained plant material, choose a quality supplier and check for contaminants. In small scale herb harvesting the problem of contamination can easily be avoided by close attention at the time of harvest.

To facilitate adequate infusion of the herb, it should be cut into small pieces (this is termed diminution), a very sharp knife on a wooden board can be used, or as at Pindari, a small chaff cutter. Chaff cutters are dangerous and require care in their use. Commercially, a hammer mill is often used for diminution of the herb.

At Pindari we selectively and carefully dry the plant material to remove the bulk of the moisture. We do this by placing the plant material in a drying room away from direct light at 24-26C for 1-2 days. The drying is done gently and in such a way so as to sustain a minimal loss of heat sensitive plant chemicals. The part drying of the plant material has advantages and disadvantages:

Advantages:

Disadvantages

It is a decision between reducing the moisture content and increasing the herb to oil ratio, and the loss of plant constituents.

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Optimising and Standardising Oil Infusions

Points to consider in preparing a standardised oil infusion of optimal and repeatable quality:

The term "comfortable" is used here to describe the degree of compression of the herb material in the macerating container, it being compacted enough to produce an infusion of high concentration, but not too compact so as to reduce or stop the infusion of the menstruum through it. 

To achieve a quality infusion with a standard high strength requires differing strategies for different plant materials. With all infusions it is best to first obtain an accurate measure of the water content of the fresh herb (see dry weight measurement further on). This provides the basis for establishing the ratio of the dry weight of the herb used to the weight or volume of menstruum into which the herb is placed.

With the manufacture of fresh herbal tinctures in mixed alcohol and water menstruums, there are established industry standard strengths but with oil infusions the author has found no recommended standards, but if making oil infusions on a regular basis, or for medical or manufacturing use, there is a need to standardise the herb to menstruum ratio so that a level of consistency of product is achieved.

For Marigold and Chamomile flowers, at Pindari a standard concentration of 1:2 (partially dry weight of herb to weight of menstruum oil) has been set as the "bench mark" strength. In practice this is around 600gm of partially dried flowers being placed into 1200gm of oil in a 2 litre glass jar.

The term "partially dried" means being dried to the extent that the bulk of the water content is removed (50 - 70%) but with the decision on when to infuse the herb being made based not only on the level of the reduction in the moisture content, but more in practice on its visual appearance, especially its colour, feel and smell. This allows for a degree of uniformity of product to be achieved that takes into consideration variations caused by seasonal and climatic factors.

An important advantage in setting procedural and strength standards in the manufacturing of oil infusions is that it provides a "base line" from which progressive improvements can be incorporated into the process as experience and a measure of the quality of the products produced is gained.

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Containers

Our experience has shown that on small scale production of infused oils it is best to use a standardised size and type of container. This provides for the standardisation of the quantities of oil and herb used for each batch. Glass is preferable, so that the infusion and its progress can be viewed and monitored. At Pindari we use a 2 litre clear glass pickle jar with a 110mm screw top cap and rounded shoulders.

The rounded shoulders of the jar facilitate the "compacting" of the herb mass by holding the surface mass of the compressed herb at or below the oil level in the jar. 

Cleaning the jar after maceration can be achieved by fully draining and then wiping the oil from the jar. Then wash with detergent and rinse well with water and finally with pure alcohol. This process will sometimes leave a slight residue of oil on the container but it avoids soap residues. The jar can then be tightly capped with the remaining alcohol keeping the jar sterile and free of mould. Or the jar can be allowed to drain and either dried in a warm dust free environment or in a warm oven.

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Batch Record Book

It is an essential manufacturing practice that a written record of each batch of infusion be kept. This record can also provide and maintain quality control details that can be referred to at a later date. Suggested headings for this record are:

  1. Name of Herb and the oil menstruum used including the oil's date of expression.

  2. Batch number.

  3. Previous batch number, date of manufacture and current stock holding.

  4. State of the Herb.

  5. Weather conditions.

  6. Harvest details.

  7. Part of the herb used and the chaffing/cutting and drying process.

  8. Infusion process.

  9. Quantities used.

  10. Macerating storage conditions.

  11. Date and the process used in expressing the oil from the marc.

  12. Comments on resultant infusion.

  13. Harvest quantity.

  14. Signature. 

It is useful to choose a batch numbering system incorporating the date so that the date of manufacture of any infusion can be readily obtained. e.g. Batch 211206A, being the day (21st), the month of December (12th), the year (2006), and the manufacturing number for the day (A etc). This enables easier stock rotation and expiry date management and can be a useful reminder of the timing for next season's harvest.

It is important when using poly-unsaturated oils that you are able to monitor the date of manufacture of the infusion and also have a record of the expression date of the oil used. This enables the application of a more appropriate expiry date.

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Dry Weight Measurement

This may be done by taking a sample of the fresh herb prior to its harvesting, cutting it into small portions or thin slices, then promptly and accurately weighing it before carefully drying with moderate heat.

A scientific method of establishing the dry weight is to take the weight of the sample and continuing the drying process until no further weight is lost. The herb can then be assumed to be dry and the percentage of water loss and thus dry weight be attained.

A simpler method is by feel and testing when any "small twigs" in the sample break sharply.

Any drying procedure is problematic in that as the moisture leaves so do any volatile oils and this can lead to inaccuracies in the dry weight calculation. 

To calculate the dry weight percentage:

dry weight of herb

 X 100
wet weight of herb 1

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Preserving Oil Infusions

The term "preserving," used in the context relating to oil infusions, applies to the reduction of the rate of oxidation of the oil and thus the extension of its shelf life.

Cold pressed and virgin vegetable oils already contain anti-oxidants being their natural chemical constituents. These and any added anti-oxidants "sacrifice" themselves to oxidation, thus protecting the unsaturated chemical bonds in the oil against oxidation, a process that leads to rancidity. 

Saturated fats and oils such as coconut oil, if "virgin," will also contain natural anti-oxidants, but as they are chemically "saturated," they are far more stable requiring less need for added anti-oxidant protection and they have a longer shelf life. The correct storage of oils is essential to extend their shelf life. The more unsaturated the oil the more critical this is.

The shelf life of oils may be extended by the addition of vitamin E, and other oil soluble anti-oxidants such as carotenes, and a liquid carbon dioxide extract made from Rosemary fronds (Proprietary Australian name of Amiox).

Choosing the least unsaturated oil that is freshly expressed and that has its own natural anti-oxidants present (i.e. a virgin oil) and to which extra anti-oxidant has been added, will give an oil infusion a longer expiry date. 

Correct storage of the infused oil as given below will further extend the expiry date.

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Manufacturing Procedure

This depends on the type of material being extracted and what is required as an end product.

When measuring the quantity of oil used, it is easier to measure by weight rather than by volume as:

Manufacturing steps:

  1. One or two days before the harvest collect a small sample of the herb and calculate its dry weight. 

  2. Harvest at a chosen time of the day and de-contaminate and "debug" the herb material.

  3. Cut the herb into the desired particle size.

  4. Dry or partially dry the herb as required.

  5. Add an anti-oxidant to the clean jar if required.

  6. Pour a measured amount of oil or liquid fat into the jar.

  7. Add the measured amount of prepared herb to the jar and slowly push the herb in and under the oil. 

  8. Use the rounded shoulders of the container to "hold" the herbal material under the oil.

  9. Leave a minimal amount of air space in the jar to reduce oxygen contact with the oil.

  10. Add a bottle cap full of pure alcohol (or brandy whisky etc.) to the jar carefully so that it floats on the oil. This will discourage mould growth and the alcohol will evaporate off when the jar is later opened.

  11. Cap well and store in a warm but dark place for 2-3 weeks.

Caution: When the infused oil and herb is warmed, the oil expands causing a possible overflow if the bottle is full. It pays to place the maceration bottle on a plate or saucer.

Examples of the Extraction Procedure 

At Pindari, four infusions are prepared, they being from Marigold (Calendula officinalis) flowers, German Chamomile (Matricaria recutica) flowers, St Johns wort (Hypericum perforatum) flowering tops and Mullein (Verbascum thapsus ) flowers.

With Marigold flowers, there is approximately an 80% moisture content (dry weight 20%). They are partially dried in darkness with a gentle flow of warm air at around 24-28C for 2-3 days until they have lost more than 50% of their weight in water and the petals have curled but with a non faded orange (carotein) petal colour.

A similar process is used for Chamomile flowers that have a circa 25% dry weight but less time is given to the drying process so as to reduce the loss of essential oils.

With St Johns wort flowers, these are dried for one day and then directly immersed in oil. 

Mullein flower petals are directly immersed in oil. 

The advantages in growing and processing your own herbs for infusion is that the growing and harvesting history of herb is known along with any drying process employed.

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Separating the Infused Oil from the Herb Material

There are two basic options for the separation of the oil from the marc with the most effective and economic depending on circumstances. These are:

Draining process - advantages:

Procedure
Drain the liquid from the marc by inverting the bottle over a large funnel containing filter paper or cloth. Large stainless funnels used in the catering industry for cooking potato chips in oil are ideal, and there is a matching filter paper used in the same industry that is adequate for the purpose of filtering the liquids draining from the bottle. The air flow over the collected liquid and the draining time should be kept to a minimum. Keep covered to reduce exposure to light and exclude dust etc.

Pressing the marc - advantages:

Procedure

First drain the bulk of the oil by inverting the maceration vessel and allowing the oil to drain through a filter as above. Remove the material from the vessel and place it in the pressure vessel, apply pressure slowly, allowing the oil to drain off, be collected and filtered. 

Pressing of the oil can be achieved by using a wine press or any of the other presses that are available. There are commercial herb tincture presses available through herbalist professional bodies.

For those without a press, placing the drained marc in a calico bag and twisting the bag vigorously at both ends will be moderately successful in expressing the oil.

For soft and small portioned herbs such as Chamomile flowers, placing the marc to be pressed in a calico bag and then in the press can prevent the strainer plates at the bottom of the pressure vessel from being clogged by plant material.

Experimentation and versatility is required to develop the most satisfactory method of expressing the oil. Recording the best methods in the batch record book can be useful when coming to express next season's harvest.

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Establishing an Expiry Date.

Establishing an expiry date for an oil infusion is dependent on many variables. All vegetable oils and especially unsaturated oils should be used as early as possible and they should be stored so their vulnerability to oxidation is minimised. Thus the choice of an expiry date is dependent on many variables including:

Some within the oil industry give oils such as Almond oil a 2 year expiry after expression.

With any product manufactured from the infused oils, its expiry date needs to be within the expiry date of the ingredients used in the manufacturing process. The more unsaturated the oil, the shorter should be the expiry date given and the greater the need for the addition of anti-oxidants and the provision of a label indicating the required storage directions.

Ken Atherton 
Pindari Herb Farm
200 Norwich Drive Longford Tas. 7301 
www.pindariherbfarm.com
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