Fish oil – cloudiness, storage and safety of use

Why does liquid cod liver oil sometimes become cloudy when taken out of the fridge, how should it be stored properly, and how can you tell when it has gone off? Check out this practical guide at , which will help you make the most of every bottle of cod liver oil – from the moment you open it to the very last drop.

Fish oil is one of the oldest and most traditional dietary supplements – it has been part of Scandinavian and Polish dietary traditions for centuries. Norwegian fish oil, produced from the livers of Atlantic cod, provides concentrated omega-3 fatty acids and fat-soluble vitamins – primarily vitamins A and D. From the perspective of the authorised health claims by the European Food Safety Authority, cod liver oil has a solid scientific basis: EPA and DHA contribute to the normal functioning of the heart (250 mg per day). DHA contributes to the maintenance of normal brain function and normal vision (250 mg per day). Vitamin D contributes to the normal absorption of calcium, the maintenance of normal bones, and the normal functioning of muscles and the immune system. However, this article does not focus on the benefits of fish oil supplementation – this is a topic we return to in other articles. Here, we will address the practical issues that people who use liquid fish oil encounter on a daily basis: cloudiness, storage, oxidation and signs of loss of freshness.

Why does fish oil in a bottle sometimes become cloudy?

This is one of the most frequently asked questions by people who store fish oil in the fridge: “I’ve taken the bottle out of the fridge and the fish oil looks different – is it still okay?” The answer is reassuring: in most cases, yes, it is fine, and the cloudiness observed is a purely physical phenomenon, not a product defect.

Fish oil contains a mixture of various fatty acids – ranging from shorter to long-chain unsaturated fatty acids. These acids have different melting points. At low temperatures (below around 8–10 degrees Celsius), some fractions of the fat begin to crystallise partially – tiny, whitish particles form, which scatter light and give the liquid a cloudy appearance. This is exactly the same mechanism that can be observed in olive oil stored in the fridge – it also becomes cloudy and may develop whitish flakes.

After leaving the bottle out of the fridge for a dozen or so minutes (on the kitchen worktop, away from heat sources), the cloudiness usually diminishes significantly or disappears altogether – the fats dissolve again and the fish oil returns to its clear state. In most cases, this is a natural, reversible process that does not affect the quality or nutritional value of the product. If, despite being warmed, the cod liver oil remains noticeably cloudy or develops unpleasant odours or flavours, it is worth considering the other signs described in the section on oxidation.

[tip: If your fish oil has become cloudy after taking it out of the fridge, leave the bottle on the kitchen worktop for 15–20 minutes before using it. In most cases, the cloudiness should disappear or diminish significantly – this is a natural physical phenomenon. If it does not return to full clarity, also check the smell and taste (you’ll find more about signs of loss of freshness later in the article).]

How to store fish oil correctly before opening

Before opening, fish oil is a stable product, but even then, storage conditions are important for maintaining full freshness and nutritional value. The key factors are temperature, exposure to light and air.

Temperature – before opening, fish oil is best stored in a cool place, at a temperature not exceeding 25 degrees Celsius. It does not necessarily have to be a fridge – a kitchen cupboard away from the oven, hob and direct sources of heat works well.

Light – Omega-3 fatty acids are sensitive to light, particularly ultraviolet light. Direct sunlight accelerates oxidation processes and may affect the product’s stability. For this reason, fish oil is sold in dark bottles (usually made of brown glass) which protect the contents from light. Nevertheless, do not leave the bottle in a visible, sunlit spot.

Humidity and cleanliness – before opening, the bottle is hermetically sealed, so ambient humidity is not a major concern. However, you should not store cod liver oil in rooms with high humidity and unstable conditions (e.g. in the bathroom).

After opening the bottle – a critical moment

Opening the bottle of fish oil sets in motion a process that cannot be stopped – the contents come into contact with the air (more precisely: with oxygen). Omega-3 fatty acids are polyunsaturated, which makes them highly valuable from a nutritional point of view, but also susceptible to oxidation. The longer the bottle remains open and the more air comes into contact with the fish oil, the faster the oxidation processes proceed.

A few practical guidelines for after opening:

Store in the fridge – once the bottle has been opened, store the fish oil in the fridge (4–8 degrees Celsius). The low temperature significantly slows down the oxidation processes and extends the product’s shelf life.

Screw the cap on tightly – close the bottle securely after each use. Every minute the bottle is left open means the contents are exposed to air for longer.

Use within the period recommended by the manufacturer – typically, once opened, fish oil should be used within 30–90 days, depending on the brand and specific formula. Check the recommendations on the packaging.

Do not pour anything back into the bottle – if you have poured out too much, do not pour the remainder from the spoon or measuring cup back into the bottle. Doing so would introduce potential bacterial contamination and accelerate the spoilage process.

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Fat oxidation – what it means and how to recognise it

Oxidation is a chemical process in which oxygen reacts with polyunsaturated fatty acids, leading to the formation of lipid peroxides, aldehydes and other compounds responsible for a rancid taste and smell. This is a natural process that occurs in all polyunsaturated fats – not just in fish oil. For anyone taking fish oil, two questions are important: how to recognise it and how to slow it down.

Signs that may indicate that cod liver oil has passed its peak freshness:

Smell – fresh cod liver oil has a characteristic, mild fishy smell (or, in the case of flavoured varieties, the smell of the added flavouring, e.g. lemon or orange). Oxidised cod liver oil usually has a sharp, pungent ‘fishy’ smell – the odour is distinctly unpleasant and reminiscent of something spoiled. This is usually the quickest indicator.

Taste – fresh fish oil has a mild, slightly milky or gently briny taste (or a flavoured taste in flavoured varieties). Oxidised fish oil usually has a sharp, bitter, pungent – ‘rancid’ – taste. If you detect distinct unpleasant flavour notes that were not present before, this is a significant warning sign.

Consistency and colour – fresh fish oil is clear (when warmed outside the fridge) and has a characteristic golden or golden-amber colour. A marked change in colour towards a darker, brownish hue, with sediments other than natural crystallisation at low temperatures, is a potential sign of oxidation.

Assessing the freshness of cod liver oil is based on the combined observation of several parameters – a single indicator (for example, a slightly altered colour on its own) is rarely sufficient grounds for replacing the product. A combination of an unpleasant odour, a bitter taste and persistent cloudiness provides a clear indication.

Orange flavour versus the ‘natural cod flavour’

Some people prefer flavoured cod liver oil (lemon or orange) – for many consumers, the addition of natural orange flavouring significantly improves the enjoyment of daily use. Others choose fish oil in its natural form, appreciating its classic, slightly briny flavour profile.

In terms of freshness, both variants behave similarly – the added flavouring does not affect the stability of the Omega-3 fats. Regardless of the form, the key to maintaining quality is to store it in the fridge after opening and to use it within the period recommended by the manufacturer.

If you’re considering fish oil for a child, special children’s formulas are available – with an adjusted dose of Omega-3 and a suitable flavour to mask the fishy taste. You can find out more in the article fish oil – a natural treasure trove of nutrients essential for health.

Fish oil with vitamin D3 – two ingredients in one supplement

Some fish oil supplements are additionally enriched with vitamin D3. This is a sensible combination for two reasons. Firstly, vitamin D is fat-soluble, so fish oil provides a natural medium for its absorption. Secondly, fish oil itself contains small natural amounts of vitamin D, but these are usually insufficient to meet an adult’s full daily requirement. The addition of a standardised dose of vitamin D3 allows this requirement to be precisely met in a single preparation.

Vitamin D3 fulfils a number of recognised functions – it contributes to the normal functioning of the immune system, the maintenance of normal bones and muscles, and the normal absorption of calcium. This makes the combination of fish oil and vitamin D3 a sensible option, particularly during the autumn and winter months, when natural vitamin D synthesis in the skin is limited in Polish conditions. You can find out more in the articles Calcium – is supplementation for everyone? and Omega-3 – what you should know about the golden ingredient of our diet.

Fish oil in a bottle vs Omega-3 in capsules

The classic dilemma for anyone starting Omega-3 supplementation: a bottle of liquid fish oil or fish oil capsules? Each form has its own practical advantages.

Fish oil in a bottle - the traditional form, economical per serving, allows for flexible dosing (from a small spoonful for a child to a larger one for an adult). It must be stored in the fridge once opened and used within the period recommended by the manufacturer. Another advantage is the natural presence of fat-soluble vitamins A and D.

Omega-3 in capsules - a more convenient form for travelling and when away from home, without the issue of a fishy taste. Each capsule is hermetically sealed to prevent air exposure, which prolongs its stability. Less flexible dosing – the serving size is fixed.

The choice between the two forms depends on personal preference and lifestyle. In practice, many people find it works well to combine both forms – fish oil in a bottle at home, and capsules for travel and trips.

[note: Vitaler’s cod liver oil comes from Norwegian waters and is produced to the highest standards of freshness. The range includes natural cod liver oil, orange-flavoured cod liver oil with vitamin D3, and a special formula for children – free from artificial colours and preservatives.]

Safety and situations requiring caution

Fish oil, when taken in typical supplement doses, is well tolerated by healthy children and adults. The most commonly observed side effects (usually mild) include temporary belching with a fishy aftertaste, mild gastrointestinal discomfort, or looser stools at high doses.

[warning: Fish oil contains omega-3 fatty acids and vitamin A. Consult your doctor about taking fish oil supplements if you are on anticoagulants (warfarin, acenocoumarol, NOACs) – high doses of omega-3 may affect their efficacy. Pregnant and breastfeeding women should choose their fish oil doses after consultation – both because of the vitamin A content (which, in very high doses, can be harmful during pregnancy) and because of the safety profile of the specific formula. People with a fish allergy should not take fish oil – look for vegan Omega-3 alternatives derived from algae. If the fish oil has a distinctly unpleasant, pungent fishy smell or a noticeably bitter taste, these are clear signs of oxidation; in such cases, it is safer to replace the bottle with a fresh one.]

The most common mistakes when storing fish oil

Leaving the bottle on the kitchen worktop after opening – storing it outside the fridge after opening significantly accelerates oxidation. Once opened , always store fish oil in the fridge.

An open bottle with the cap unscrewed – even a few minutes with the bottle open means significant exposure to air. Screw the cap back on tightly after each use.

Storing fish oil next to a hob, oven or in a sunny spot – proximity to heat sources and direct sunlight are the two biggest enemies of fish oil’s freshness. Choose a cool, dark cupboard before opening, and the fridge once opened.

Using the same teaspoon for fish oil and other products – keep a dedicated, clean teaspoon for fish oil or – even better – use the measuring spoon provided with the bottle. You’ll find our full range of Omega-3s in the Omega Acids category, and vitamins to support a healthy routine in the Vitamins category.

FAQ – frequently asked questions about storing fish oil

Can I freeze fish oil to extend its shelf life

Freezing fish oil is not recommended. Although it would theoretically slow down oxidation processes, the crystallisation of fatty acids at very low temperatures can alter the product’s structure, and the processes of defrosting and refreezing are problematic. Stick to standard refrigeration after opening.

Is fish oil that has become cloudy still safe to consume

In most cases, yes, provided the cloudiness is due to low temperature (after removal from the fridge). After leaving the bottle out of the fridge for a dozen or so minutes, the cloudiness usually diminishes significantly or disappears altogether – this is a natural physical phenomenon. However, if the cloudiness persists despite warming, and unpleasant odours or a bitter taste also develop – this is a sign that you should assess the cod liver oil on multiple parameters (smell, taste, colour) and, if in doubt, replace it with a fresh one.

How long after opening does cod liver oil lose its freshness?

The typical period of optimal freshness for opened cod liver oil, when stored correctly (in the fridge, in a tightly sealed bottle, protected from light), is 30–90 days – check the manufacturer’s specific recommendations on the packaging. After this period, the fish oil may still be safe to consume, but its flavour and aroma profile, as well as the content of certain unsaturated fatty acids, may no longer be optimal.

Can a fresh bottle of fish oil go off?

This is a rare but possible scenario – if the fish oil was stored in unsuitable conditions before reaching the consumer (for a long time at high temperatures, in direct sunlight, or during transport) or has passed its use-by date. Before using a new bottle for the first time, check the smell and taste. If you have any doubts, contact the retailer.

Summary: Fish oil is a valuable dietary supplement with health claims firmly endorsed by the EFSA – providing omega-3 fatty acids (EPA and DHA) and, in fortified versions, vitamin D3. The practical aspects of its use – cloudiness in the fridge, oxidation after opening, and signs of loss of freshness – are well understood from a physical perspective and should not give rise to unnecessary concerns. Cloudiness after removal from the fridge is a natural physical phenomenon which, in most cases, diminishes significantly or disappears after a dozen or so minutes outside the fridge. Once the bottle has been opened, store the fish oil in the fridge, screw the cap on tightly after each use, and use it within the period recommended by the manufacturer. An unpleasant, pungent fishy smell and a bitter taste are clear signs of oxidation – in such cases, it is safer to replace the fish oil with a fresh bottle. Handling fish oil with care allows you to make full use of every bottle – from the first to the last portion.