Linseed oil, also known as flaxseed oil, is a versatile oil derived from the seeds of the flax plant. It has been used for centuries in wood finishing, as a preservative, and in oil paintings. As a drying oil, linseed oil hardens over time when exposed to oxygen. This makes it useful as a wood finish and binding medium in oil paints.
However, like any natural product, linseed oil has a limited shelf life. Oxidation causes linseed oil to thicken and eventually become rancid. This leads many to wonder: does linseed oil expire and is there a definite expiry date?
What is Linseed Oil?
Linseed oil, also known as flaxseed oil, is derived from the seeds of the flax plant (Linum usitatissimum). The oil is obtained through pressing and sometimes followed by solvent extraction.
Raw linseed oil is composed primarily of glycerides of linolenic acid, linoleic acid, and oleic acid. Linolenic acid comprises approximately 50-60% of the fatty acid composition. This high concentration of polyunsaturated fatty acids contributes to linseed oil’s quick drying properties.
When exposed to oxygen, the polyunsaturated fatty acids undergo oxidation and polymerization. Crosslinking of the fatty acids causes the oil to transform into a solid film. The ubiquitous use of linseed oil as a wood finish is owed to this drying capacity. As the oil “dries,” it hardens into a protective, water-resistant layer.
Besides its use as a wood finish and binding medium in oil painting, linseed oil also has nutritional value. It provides a rich source of the omega-3 fatty acid ALA (alpha-linolenic acid). Linseed oil is sometimes used as a nutritional supplement.
With an array of uses, from woodworking to nutrition, linseed oil is a versatile oil. But there is confusion over its shelf life and whether linseed oil expires.
Does Linseed Oil Expire?
Yes, linseed oil does eventually expire and go rancid. Oxidation causes linseed oil to thicken and develop an unpleasant odor and taste.
Rancidity is associated with the breakdown of fatty acids into peroxides and aldehydes. These compounds have strong, bitter flavors and odors. As oxidative stability decreases, rancidity increases.
Because raw linseed oil consists mostly of polyunsaturated fatty acids, it is particularly prone to oxidation. Polyunsaturated fats have multiple double bonds in their hydrocarbon chains which are vulnerable points of attack for reactions with oxygen. Saturated and monounsaturated fatty acids are comparatively more shelf stable.
The main factors impacting the shelf life of linseed oil are:
Oxygen Exposure
Exposure to oxygen is the primary cause of linseed oil degradation. Oxygen enables autoxidation of the hydrocarbon chains in fatty acids. Minimizing contact with oxygen after opening can extend the shelf life of linseed oil. Purchasing linseed oil in tins helps prevent oxygen exposure as compared to plastic bottles.
Light Exposure
Light provides energy to power photosensitized oxidation of linseed oil. Keeping linseed oil stored in darkness helps maintain stability.
Heat
Increased temperature accelerates the rate of oxidation. Storing linseed oil in a cool, dark place, such as a refrigerator, pantry, or cupboard helps prolong its shelf life.
Storage Time
The storage time allowed before linseed oil is considered expired depends on storage conditions and oil processing.
Container
The container material impacts exposure to oxygen and light. Tinted glass and metal tins provide the best barrier to oxygen and light for extending shelf life.
Oil Processing
Raw linseed oil has a shorter shelf life than types of processed oil due to the high polyunsaturated fat content. Boiled linseed oil has improved stability due to polymerization of some fatty acids. Solvent extracted and alkali refined oils also have enhanced stability.
With optimal storage conditions, raw linseed oil may last around 6 months. However, linseed oil can start developing rancid odors in as little as 8 weeks after opening if improperly stored.
How to Tell if Linseed Oil Has Gone Bad
Rancidity is the primary indicator of spoiled linseed oil. Signs your linseed oil has gone bad include:
– Strong, unpleasant odor – Rancid linseed oil smells bitter, unpleasant, and “off”
– Change in texture – The oil becomes thicker and clumpy
– Color change – The oil darkens in color to amber-yellow or brown
– Poor performance – Rancid oil loses effectiveness as a wood finish and takes much longer to dry
If your linseed oil has any rancid odors or is thicker and clumpier than a new bottle, it has likely gone bad. Discard linseed oil at the first signs of spoilage.
You can conduct simple tests to check your linseed oil for rancidity at home. Taste a small amount to check for a bitter taste or smell the oil for any unpleasant odors. You can also spread a thin layer on a sheet of glass or wood to see if the oil still dries properly. Good linseed oil should dry to the touch within 24 hours.
How to Store Linseed Oil Properly
Follow these tips for maximizing the shelf life of your linseed oil:
– Purchase small quantities and use within 6 months
– Select tins or tinted glass bottles to limit oxygen and light exposure
– Keep oil containers tightly sealed when not in use
– Store in a cool, dark place like the pantry or refrigerator
– Transfer oil to a smaller container once opened if not using quickly
– Never store linseed oil near heat or flames
– Avoid transferring back and forth between multiple containers
– Wipe dip tubes clean and replace lids tightly after each use
Proper storage helps retard oxidation and prolong the shelf life and quality of linseed oil. But linseed oil will eventually expire and go rancid even in ideal storage conditions. Purchase only as much as you expect to use within 6 months.
How Long Does Linseed Oil Last?
With optimal storage, raw linseed oil may last:
– 6-12 months when stored unopened in a cool, dark place
– 4-6 months when opened if transferred to minimal air container and stored in cool, dark place
– As little as 8 weeks when stored opened at warm temperatures with exposure to light and oxygen
The shelf life varies based on storage methods after opening. Raw linseed oil in the original container may only last 2-3 months in a hot environment. Refined linseed oils have enhanced stability and may last 1-2 years sealed and stored properly.
If purchasing from bulk containers at a big box store, it is best to transfer linseed oil into tinted glass bottles for storage. Purchase linseed oil in sizes you will use quickly. Discard opened linseed oil after 6 months, even if stored optimally and there are no signs of rancidity yet.
Signs Your Linseed Oil Has Expired
Watch for these indicators that your linseed oil is past its prime:
– Strong bitter, rancid odor
– Viscosity thickening, clumping texture
– Darkening brown and amber color
– Improper drying if used as a wood finish
Linseed oil can go rancid soon after opening if stored at warm temperatures. Always do a sniff test and look for changes in texture and color before using linseed oil. Discard linseed oil that smells rancid or bitter immediately.
Can You Use Linseed Oil After Expiry?
It is not recommended to use linseed oil past its expiration or if it has gone rancid. Rancid linseed oil will not dry properly and loses effectiveness as a wood finish. Consuming rancid linseed oil may also pose health risks.
Rancid oil contains degradation products like aldehydes, peroxides, and other volatile compounds you do not want in your finished wood projects or ingested.
Certain processing methods may extend the shelf life of linseed oil, but there is no way to reverse rancidity once it occurs. It is best to discard linseed oil at the first signs of spoilage. Purchase a fresh bottle once your current supply goes rancid.
Does Boiled Linseed Oil Go Bad?
Yes, boiled linseed oil can also go rancid with age. Boiled linseed oil is raw linseed oil that has been processed to improve drying properties and stability. The oil is heated with metallic dryers which catalyze polymerization of the fatty acids.
This treatment reduces the unsaturated fat content and results in a thicker oil. Boiled linseed oil generally has a shelf life of 1-2 years when stored in sealed containers in a cool, dark place.
Proper storage is still important to prevent boiled linseed oil from eventually oxidizing. Rancidity is indicated by unpleasant odors, color darkening, and loss of performance. Discard boiled linseed oil once it goes rancid.
What Happens if You Use Rancid Linseed Oil?
It is inadvisable to use linseed oil that has gone rancid. Potential risks of using spoiled linseed oil include:
– Poor wood finish – Linseed oil is renowned for use as a wood finish and protecting agent. Rancid oil loses this effectiveness and the finish may remain tacky or soft. Using rancid oil defeats the purpose of applying linseed oil.
– Safety concerns – Rancid oils contain oxidized fatty acids and degradation compounds like aldehydes, peroxides, and reactive radicals. Ingesting rancid oils may pose health risks. Volatile organic compounds released from rancid oil can also cause respiratory irritation.
– Unpleasant smells – Rancid linseed oil has a bitter, unpleasant odor. This can transfer to your woodworking projects and anything else that comes into contact with rancid oil.
– Contamination – Rancid oil can contaminate solvents like mineral spirits, turpentine, and other finishing products if equipment is not cleaned properly after use.
Your best option is to discard linseed oil at the first signs of rancidity. Thankfully, linseed oil is readily available at art supply and hardware stores when you need to purchase a fresh bottle. With proper handling and storage, you can maintain quality and prolong the shelf life of your linseed oil.
Frequently Asked Questions
Does linseed oil need to be refrigerated?
Refrigeration can help prolong linseed oil’s shelf life, but it is not required. Linseed oil can be stored at room temperature in a cool, dark cupboard or pantry. Refrigeration helps retard oxidation but is more important after opening.
How long does linseed oil last when opened?
When stored properly in a full, tightly sealed container, opened linseed oil may last around 4-6 months. However, linseed oil that is exposed to air, light, and warmer temperatures may start going rancid within 8 weeks of opening.
Can old linseed oil make you sick?
Rancid linseed oil contains oxidized compounds that can cause minor stomach upset if consumed. Rancidity also produces potentially irritating volatile organic compounds. Old linseed oil loses nutritional value but is not highly toxic. Still, rancid oil is best discarded and fresh linseed oil used for health and safety.
Does linseed oil have an expiration date?
Linseed oil does not have a definite expiration date printed on the container like some food products. The shelf life depends on storage conditions. An unopened bottle may last 1-2 years in a cool, dark place. Once opened, linseed oil slowly oxidizes so it is best used within 6 months.
Can linseed oil spontaneously combust?
Linseed oil can self-heat and spontaneously combust under certain conditions. Oil-soaked rags are a fire hazard due to this risk of spontaneous combustion from rapid oxidation. Never leave linseed oil rags in a pile. Fully dry rags outside laying flat or store in sealed, water-filled metal container.
Conclusion
Linseed oil is susceptible to oxidation and eventual rancidity due to its high concentration of polyunsaturated fatty acids. Proper storage to minimize exposure to air, heat, and light can prolong the shelf life to about 6-12 months. Look for changes in odor, texture, color, and performance to determine if linseed oil has expired. Rancid, expired linseed oil should be discarded. With careful handling, linseed oil can be a long-lasting addition to any artist or woodworker’s supplies.
