Shelf life and storage

A properly stored botanical extract stays close to its initial state for a long time. Kept in a full, tightly closed container in a cool, dry, dark place, an extract changes slowly. Three factors drive change: air (oxygen), light, and heat. Storage means keeping these three away. This is no different from storing cooking oil and spices in a kitchen. Change happens over months and years. How long it lasts also depends on the extract type.

Why does an extract change?

The three factors that change an extract are air, light, and heat. A review on essential oils lists these three as the primary factors affecting quality [1].

Air. Oxygen slowly reacts with extract components. This is called oxidation. In essential oil, oxidation lowers quality, and the fresh scent flattens over time [1]. In fixed oil (non-volatile oil from seeds), oxidation causes rancidity [2].

Light. Light converts some components into other components. In a 90-day trial on leaf oil from a black pepper relative, light changed the composition, while temperature had little effect [3]. Immortelle oil was found most sensitive to light in a one-year trial [4].

Heat. Heat speeds up reactions, and the lightest components decrease by evaporation [5]. In experiments, this effect becomes pronounced under warm and bright conditions. A fresh-scented component of rosemary oil did not change at room temperature in the dark for three weeks. It decreased only at 38 °C and under continuous light [6].

Which extract is more sensitive?

Light-scented components, some seed oils, and pigments are more sensitive to air and light. Some extracts carry their own protective substances and remain unchanged for a long time.

Essential oil and volatile fraction. Each oil changes in its own way, and some are very stable. When juniper oil was stored for one year under different conditions, its total composition did not change significantly. The oil was found stable [4]. The volatile fraction, the light cut of CO₂ extraction, acts like essential oil.

Fixed oil. The air sensitivity of seed oils depends on fatty acids. As the polyunsaturated fatty acid content (fatty acids that react easily with air) rises, the oil oxidizes faster [2]. In an accelerated test of five edible oils, grape seed oil, which has the most of these fatty acids, lasted the shortest [2].

Colored extract. Pigments fade most in light. Darkness and cold protect them. Carotenoids (yellow, orange, and red pigments) give paprika CO₂ extract its color. When this extract was stored at 5 °C in the dark for one year, it kept 95% of its carotenoids. When the same extract stood at room temperature in daylight for one year, about 70% of its carotenoids remained [7].

Extract carrying its own preservative. Some extracts contain the plant's own antioxidants (substances that slow oxidation). Ginger oleoresin (oily extract carrying both aroma and taste of the spice) from CO₂ extraction was kept at 0, 20, and 40 °C for 180 days. The amount of protective substances and antioxidant capacity did not drop at any of the three temperatures [8].

How to store?

In short: in a full and tightly closed container, in a cool, dry, and dark place. Each stops a separate factor.

Full and dry container. Air left above the product in the container is a source of oxygen. In dried, fully filled, and tightly closed geranium oil, main components did not change much over 24 months. Oil in a half-full container with some water mixed in changed significantly [9]. If product is taken often from a large container, divide it into small containers. This reduces the product exposed to air at each opening. Some technical data sheets require nitrogen blanketing of the headspace after each sampling. Nitrogen replaces air.

Cool storage. Cool-stored extract lasts longer. Cold-pressed rapeseed oil was best preserved at 4 °C for 12 months [10]. For lavandin oil, the best storage was low temperature and keeping air and water away [5].

Darkness. Lightproof dark glass or metal containers block light. In colored extracts like paprika extract, darkness preserves color [7].

Product coming out of cold. In a refrigerator or cold storage, some extracts thicken, cloud, or solidify. This is not spoilage. When the product reaches room temperature or is gently heated in a warm water bath, it flows again and is stirred before use. Do not open a container from cold storage before it reaches room temperature. If a cold container is opened, moisture from the air condenses inside and water gets into the product.

How to tell if it changed?

The first sign is scent and color. Measurement gives the definitive answer.

Scent and color. An extract whose scent flattens or whose color fades has started to change. In paprika extract, the color value dropped along with the carotenoid content [7].

Peroxide value in fixed oil. The freshness of fixed oil is measured by peroxide value. This value measures the first products of oxidation and rises as oil oxidizes [2]. The technical data sheet of fixed oils includes a peroxide value line.

Component profile in essential oil. Change in essential oil is seen through GC-MS and GC-FID analysis. In a citrus oil stored at different temperatures for nine weeks, fresh-scented components decreased, and oxidation products increased. The authors propose this change as an oil quality indicator [11].

What does shelf life on the document mean?

Shelf life depends on a condition. In the technical data sheet (TDS), duration and storage condition are written together, such as "store in a cool and dry place, keep away from intense light and high heat, 24 months". The duration applies when the product is stored in its closed original packaging under this condition. The production date appears on the certificate of analysis (CoA), and shelf life is read with it.

If conditions change, duration changes. A warm warehouse, a shelf exposed to light, or a frequently opened container accelerates change. Some extract documents require storage in a refrigerator (2 to 8 °C). This condition is part of the shelf life for that product.