The refrigerator test for olive oil – the most common myth. A guide to selecting, testing, and tasting olive oil

From the author

The subject of this article is complex and full of specialised topics that may seem complicated to a layperson. I have tried, however, to present it as comprehensively as possible and in accessible language. The information was drawn from the best experts in the field, whose knowledge and experience helped me gather the most important facts. I had the privilege of attending lectures and workshops led by this team during my training as an olive oil sommelier.

• Dr Agustí J. Romero – head of the olive growing and olive oil technology team at IRTA (Instituto de Agrifood Research and Technology) in Spain. For over 30 years he has specialised in improving the quality and sensory evaluation of extra virgin olive oil.
• Dieter Oberg – co-founder and chairman of the German DOP sensory working group, lecturer in organoleptic evaluation at the Zurich University of Applied Sciences, and juror at numerous international olive oil competitions.
• Manolis Salivaras – founder and head of Multichrom.lab in Athens, an expert in chemical and organoleptic analysis of olive oil, with extensive experience in running sensory panels and international quality certifications.
• Prof. Maurizio Servili – professor at the University of Perugia (Italy), author of nearly 180 scientific publications, focused on technological improvements to the milling process and on the study of phenolic and volatile compounds that influence the flavour and stability of olive oil.
• George Dervitsiotis – agronomist responsible for crop control at the international company Mediterre Eurofood, specialising in optimising olive tree growing conditions and sustainable agricultural practices.

This is only a small fraction of the vast body of knowledge on olive oil. I also draw experience and skills from leading producers who – to my great fortune – are happy to share their expertise. I hope this article will introduce you to the most important and interesting topics. If the subject piques your interest, I encourage you to consult publications by the specialists mentioned above.

The Polish word "oliwa" literally means "the juice pressed from olive fruits", so the phrase "olive oil from olives" is a tautology. The term "EVOO" (extra virgin olive oil), often used in the literature, denotes the highest-quality olive oil – cold-pressed, with low acidity and exceptional flavour and aroma.

A popular home method of checking the quality of extra virgin olive oil (EVOO) is the so-called fridge test. According to this method, if olive oil placed in the fridge for several hours thickens or solidifies, it allegedly proves its high quality and authenticity.

Why has the fridge test become so well known?

The method seems credible because extra virgin olive oil contains natural waxes and long-chain fatty acids that crystallise or thicken at low temperatures. That is why many consumers believe it allows them to tell real olive oil apart from cheaper blends with refined oils.

UC Davis Olive Center scientific experiment

Researchers at the renowned olive oil research centre – UC Davis Olive Center, operating at the University of California – decided to verify this popular myth. They tested seven samples: high-quality extra virgin olive oil, lower-quality extra virgin, blends of olive oil with other oils, and refined vegetable oils. The samples were kept in a refrigerator at 4.7°C for over a week. You can read the full study results here (PDF).

The results of the experiment were as follows:

• After 60 hours, none of the samples showed any change.
• After 120 hours, only the samples containing at least 50% virgin olive oil showed minimal cloudiness.
• After 180 hours, cloudiness was more visible, but none of the samples solidified completely.

Conclusion: the fridge test is not a reliable way to assess the quality or authenticity of olive oil.

Why doesn't the fridge test work?

The thickening of olive oil in a fridge depends on many factors, such as:

• olive oil contains between 55% and 83% oleic acid, with the remainder made up of polyunsaturated and saturated fatty acids, waxes and phytosterols – which leads to different solidification points (not always above 4–5°C);
• similar solidification can be observed in refined oils with a high oleic acid content, even though they are not olive oil;
• different olive cultivars, climatic conditions and harvest timing affect the profile of waxes and long-chain fatty acids, changing how olive oil behaves at low temperatures;
• the degree of wax and sediment removal (filtration) and the way the oil is stored determine the amount of substances that cause cloudiness;
• climatic conditions and the method of harvesting;
• the production and pressing method.

So how do you actually recognise good olive oil?

The best olive oil producers care not only about the pressing process and quality control, but also about making sure their products reach consumers only through authorised, trusted partners – distributors who have real knowledge of the product, of correct transport and storage conditions, and who can provide genuine advice. A reputable brand that invests in laboratory testing, enters international competitions and wins awards cannot afford fraud or quality compromises – this is the foundation of its reputation on the market. Such companies focus on full transparency and on educating both customers and resellers.

"Good olive oil" is a very general term – it should be properly matched to specific needs and uses. Our customers very often ask for "the best one"; we know that, with such a wide choice, this is not easy, but unfortunately there is no single oil that is better than all others. Before buying, you should ask yourself: what am I looking for – simply olive oil, or extra virgin olive oil (EVOO)? Our shop offers exclusively extra virgin olive oils. If you are looking for EVOO, it's worth distinguishing between its uses:

• Oils for everyday cooking and frying – it does not always have to be the highest class (extra virgin – EVOO). What matters here is freshness, the absence of defects and an honest composition – even a virgin olive oil will be safe and stable at high temperatures, although it won't deliver as many health-promoting compounds. The smoke point of extra virgin olive oil is around 190–210°C, and of virgin olive oil around 210–215°C. Such oils most often come in aluminium tins of 0.5 L, 1 L, 1.5 L, 3 L and 5 L.
• Oils to be used raw (e.g. on salads, bread, as a finishing touch on dishes) – here, it is worth choosing a first-press extra virgin oil, ideally with a medium or possibly high (not extremely high) polyphenol content ("medium phenolic EVOO", "high phenolic EVOO"), a fresh aroma, fruitiness, and balanced (harmonious) pungency and bitterness. Such oils offer a full range of flavours and health benefits and enhance the taste of dishes. They are usually packaged exclusively in suitable glass containers.

• Olive oils for health prevention (oils with the EU health claim under Regulation 432/2012) – if you care about antioxidant, anti-inflammatory or cardiovascular benefits, look for oil whose parameters are confirmed by up-to-date biochemical testing, with measured polyphenol content: by NMR (nuclear magnetic resonance) or the less precise HPLC method. The minimum for the health claim is 250 mg of polyphenols per kg, but bear in mind that time since harvest, packaging type and storage can degrade this value by up to 70% over a year. Always check the current biochemical analysis, the polyphenol analysis, pesticide screening, etc. Where possible, choose organic oils certified BIO (the entire production chain is controlled from producer to distributor). Ask the distributor about their own certificate for selling organic products (the so-called certificate for trade in organic products – the law prohibits trading in such products by entities without their own certification). You can find the register of producers and distributors of BIO/Organic products at this link. Demand for products in this class is usually higher than supply, there are no special offers or promotions, and such oil cannot be bought on a regular shop shelf or in a supermarket. For many reasons – production costs and others – prices start from around 20 EUR/500 ml (24/25 harvest) and go up, depending on the composition, polyphenol and vitamin content and the producer. One example from our offer is Olive Poem "a drop of health" – each year most of the production for the upcoming season is reserved and sold even before the harvest (very good value relative to its composition). Such oil is used, for example, in the "Nemechek Protocol" (as a part of therapy for people on the autism spectrum). It is supplied exclusively in proper glass bottles of 250 ml, 500 ml, or in so-called "pouch" packaging up to 750 ml.

Rule of thumb – if you know the producer and trust them, try the oil; if you like it, buy it. If you are buying in a shop or online, ask for current test results and documentation. Verified producers care not only about quality but also about transparency and the freshness of test results (biochemical, NMR, pesticides). Always ask about freshness, storage and transport conditions, and about real quality parameters (not just marketing slogans – for instance the industry's magic word "02" and the like).

1. Olive harvest date

The best quality is found in oils whose harvest date is no more than 12–15 months in the past. Fresh olive oil contains more beneficial nutrients and has better flavour and aroma. Olive oil loses aroma and part of its polyphenols over time, so it is always worth choosing the most recent harvest available. The oil with the highest health-promoting value is produced at the start of the harvest (green, unripe fruits are collected – only those carry the full nutritional richness), in some regions even from September. Such oil is called "early harvest". The cheapest oil is produced at the end of the harvest, between December and February (much less fruit is used per litre of oil) – usually a culinary oil sold in large tins. Honest producers/distributors describe the season as straddling two years, e.g. "harvest 2024/2025". An oil marked simply as fresh "2025" and available on the market in 2025 may be the cheapest, end-of-harvest type.

A significant group of consumers prefers mild oils, free from intense attributes such as pungency or bitterness. In that case, the best option may be to buy a high-quality oil from the previous season, in which these features have naturally diminished. Bear in mind, however, that such a mild oil contains only small amounts of polyphenols and vitamins, which are responsible for its health-promoting properties.

2. Quality and origin certificates

Look for certificates such as:

• PDO (Protected Designation of Origin)
• PGI (Protected Geographical Indication)
• COOC (California Olive Oil Council)

These certificates guarantee that the product has passed rigorous chemical and sensory tests and – most importantly – that the fruit was sourced from a specific region (for example: not every olive oil whose packaging suggests it comes from Crete actually does).

3. Organic (BIO) olive oil

Organic oils marked BIO, coming from organic farms without pesticides, synthetic fertilisers or GMOs, are a good choice – they offer full naturalness and safety. Such an oil should have up-to-date testing for pesticide residues and mineral oil hydrocarbons, as well as a current, verifiable certificate from a control body. The seller/distributor is required to hold their own BIO certificate to trade in such products.

4. Biochemical test results and how to interpret them

• Polyphenols – according to EU Regulation 432/2012, olive oil containing ≥ 250 mg of polyphenols per kg shows proven health benefits (antioxidant, anti-inflammatory effects, among others). The best oils from early harvests can contain over 2,000 mg/kg of polyphenols – this is rare and an enormous health asset.
• Acidity – for the extra virgin class, the value must be < 0.8%, and in premium oils often < 0.3%. Acidity represents the content of free fatty acids – the lower it is, the fresher and higher-quality the oil. This value can be measured only in a laboratory and should not be declared directly on the label (e.g. "0.2%"), because acidity can rise during improper bottling, transport or storage. Producer markings such as "02", "O-2", "O2" and similar are marketing devices; only current biochemical analyses confirm the real parameters.
• Peroxide value (PV) – an indicator of olive oil freshness and the presence of peroxides formed during fat oxidation. For the extra virgin class, the peroxide value must be < 20 meq O₂/kg, but truly fresh, high-quality oils have values < 10. The lower the value, the better the protection against oxidation and the longer the product's shelf life.
• K232, K270 and ΔK coefficients – the so-called UV parameters, measured by spectrophotometry:
  • K232 – assesses the presence of peroxides (primary oxidation products); permissible value: ≤ 2.50; fresh oils: often < 2.00.
  • K270 – assesses compounds formed during further decomposition of the oil (secondary oxidation products); permissible value: ≤ 0.22; in premium oils: < 0.15.
  • ΔK – a parameter that detects adulteration or the presence of refined oils; permissible value: ≤ 0.01.
  These parameters are important in assessing the authenticity and freshness of olive oil and allow detection of any production irregularities or adulteration.
• MOSH/MOAH (mineral oil hydrocarbons) – a group of chemical compounds whose presence in food (including olive oil) is very strictly controlled, as they may originate from industrial contamination or contact with packaging. In olive oil analyses, the following are checked:
  • MOSH (Mineral Oil Saturated Hydrocarbons) – fractions C10-C16, C17-C24, C25-C35, C36-C50 and the total C10-C50;
  • MOAH (Mineral Oil Aromatic Hydrocarbons) – fractions C10-C16, C17-C35, C36-C50 and the total C10-C50.
  The highest-quality oils should show MOSH and MOAH levels below the limit of quantification (< 1.0 mg/kg) – meaning a practical absence of contaminants. This confirms the product's safety and the producer's high technological standards.
• Pesticide residues – professional laboratories use advanced gas chromatography with mass spectrometry detection (GC/MS-MS), which can detect even minimal amounts of plant protection products. The best oils have results confirming no detectable pesticide residues.

In our shop Kreta24.pl you will find olive oils for which we provide official biochemical analysis results – including polyphenol content, acidity, peroxide value (PV), UV parameters (K232, K270, ΔK), NMR analyses, MOSH/MOAH testing, pesticide residues, and the official panel-based organoleptic evaluation. This gives you a full guarantee of the product's quality and authenticity.

We also offer professional biochemical olive oil testing services in a renowned laboratory in Athens. See details: Olive oil quality tests. In particular the simplest and cheapest test – the results can be surprising.

5. Storage conditions at the producer

The highest-quality olive oils are stored in cooled, hermetic stainless steel tanks under a nitrogen atmosphere, which minimises contact with oxygen and stabilises both health-related and sensory parameters.

6. Packaging – what to choose?

Bag-in-Box ("pouch"): multilayer bags in a cardboard box with a tap are currently the most functional and convenient solution for fresh oils. Research at the University of Ioannina has shown that it preserves olive oil quality much longer than tins – it protects against oxygen and light, is convenient to use and environmentally friendly. Daily use does not draw air inside or cause continuous oxidation (as happens with aluminium tins). More on this in another article.

Dark glass bottles: classic and elegant – the best choice for the highest-quality oils. They protect against UV light, are sealed with a hermetic cap – ideal for extra virgin oils used raw. A good-quality glass bottle, together with a special non-refill cap and label, can cost the producer up to 5 EUR, but it guarantees protection of the aroma and health-promoting value.

Steel tins: durable and light, but they can react chemically with the oil, especially during long storage. They are better suited for oils used daily for cooking but are not the best choice for long-term storage of premium oils. Avoid unfiltered oil in such packaging – after a short time it can react with the welds inside the tin.

PET bottles: not recommended for higher-quality oils – they offer poor protection against light, and in some cases compounds such as BPA may migrate. They can be used for an economical cooking oil, but not for extra virgin and premium ones. This is the cheapest packaging form for the producer, and a conscious consumer should avoid it.

More on optimal packaging – how bag-in-box works and why it's worth investing in good-quality glass – in our article: Olive oil packaging – Bag-in-Box vs bottles and tins.

7. Sensory evaluation

For an oil to be classified as extra virgin (the highest quality category), it must pass not only chemical tests but also the panel-based sensory evaluation according to the standards of the International Olive Council (IOC).

This evaluation is performed by a trained panel of tasters (the so-called panel test), who assess the olive oil sample with respect to:

• Fruitiness – aromas and flavours resembling fresh olives and other natural notes (green leaves, apple, almond, artichoke). The median (a mathematical value more resistant to extreme outliers than the arithmetic mean; it better represents the "typical" value in a set when the data are highly variable – the extreme readings from the panel of sommeliers are discarded) must be greater than 0.
• Bitterness – a natural element, especially present in oils with a high polyphenol content.
• Pungency – a burning sensation in the throat, linked to the presence of strongly anti-inflammatory oleocanthal (sometimes called "natural ibuprofen").

At the same time, extra virgin olive oil must not show any sensory defects (e.g. mustiness, smell of spoiled fruit, metallic odour, etc.). On the IOC scale, the median of defects must be exactly 0.

Only oils that receive a positive result in the sensory panel and meet the chemical standards (including acidity < 0.8%, a low peroxide value and appropriate UV parameters) can legally be labelled as "extra virgin olive oil – EVOO".

High sensory quality is often also confirmed by awards from international competitions, where aroma, flavour, balance and complexity are evaluated. Importantly – it's worth checking in which category the awards were given: for quality, for organic class, for high phenolic, or for example for packaging design. Marketers can be very clever in placing rows of award logos on packaging, which strongly influences consumer perception.

8. International competitions

If you value quality and look for a "gourmet" product, choose olive oils awarded at competitions (many of them are in our offer). The most prestigious ones are:

• Olympia Health & Nutrition Awards
• Berlin GOOA
• Athena IOOC
• London IOOC
• NYIOOC – New York
• Leone d'Oro – Italy
• Olive Japan – Japan

Summary

The fridge test is not a reliable way to assess olive oil quality. Instead of relying on myths, focus on objective quality parameters and certificates, and on trusted producers.

In our shop Kreta24.pl you'll find a wide selection of olive oils from renowned, award-winning producers. For most of them, we provide detailed biochemical analysis results, including NMR analyses, pesticide screening and official panel-based organoleptic evaluations performed by professional tasters.
We guarantee full transparency about the quality of our products – you can be sure that you are choosing olive oil confirmed by independent testing.

Fun fact: world record in polyphenols – Sparta Medicinal Green Label

TIP: Buy olive oil like a PRO! How to choose a good olive oil and recognise a poor one – a professional, step-by-step test

Planning to buy olive oil on holiday, at a market, in a shop or at the producer's? Take with you a professional olive oil tasting glass! It's a light, practical accessory that lets you check the oil exactly the way professional tasters do on a sensory panel (you can also use an ordinary container).

Step 1 – Aroma test according to the IOC (International Olive Council) standard

1. Pour about 15 ml of olive oil into the tasting glass and cover it (e.g. with a watch glass – also available in our shop). The colour of the professional glass is "cobalt blue" – do you know why? The colour of olive oil has no bearing on quality, yet our brain tends to suggest that "greener" is better; a taster cannot be influenced by this.
2. Warm the glass in your hands by rubbing its bottom with your palm for 1–2 minutes – the oil should reach about 28°C (a professional panel uses special heaters with temperature stabilisation – also available in our offer).
3. Remove the cover and slowly smell the oil, inhaling the aromas deeply. You are using the so-called orthonasal smell – the classic one. It's the smell we perceive when sniffing the oil in the glass – from outside, through the nose. What do you sense? Freshly cut grass? Tomatoes, citrus? Banana, artichoke, or perhaps completely different aromas – you'll find the full list at the end of the article.
4. Rate the intensity of the fruity aroma on a scale from 1 to 10 according to the standardised method (find the point on the image where the smell is still perceptible and note your score – remember to perform the test in a closed room and avoid smoking for at least an hour beforehand).

The higher the score, the fresher, more aromatic and higher-quality the olive oil. This is a practical way to avoid blind buying and to consciously choose the best product – even when shopping on holiday! If you are testing an oil with a declared organoleptic profile, you can check whether your assessment is close to that of the professionals.

Does your sample smell fresh, mature, or perhaps flat and without character?
Professional olive oil tasting glasses – available in our shop

Step 2 – Tasting olive oil like a professional: the technique and the role of retronasal smell

After analysing the fruitiness and aroma of the oil (panel test – orthonasal smell), move on to the tasting stage, which engages both smell and taste. This is where you'll discover the oil's full profile.

• Take a small sip of olive oil (about 5 ml).
• Spread it slowly across the whole mouth – from the front of the tongue, through the sides, to the back of the throat. Different parts of the tongue pick up different tastes: bitterness, pungency, sweetness, sourness and saltiness.
• A very important point: bitterness and pungency are positive attributes of a good olive oil.
• Draw a little air through your mouth – this is the so-called "strippaggio" technique, a quick inhalation of air through the teeth which mixes the oil with air and amplifies its aroma. This allows aromatic compounds to reach the back of the nose (retronasal smell), where we register the aromas released after swallowing the oil.
• Between samples, neutralise the taste – eat a slice of green apple and drink some water. Wait 10–15 minutes before trying the next oil.
• Always start with milder samples before moving on to stronger ones.
• Note down the aftertaste – the sensations that appear after swallowing or spitting out the oil: their intensity, duration and any defects. What do you feel first – pungency or bitterness, or the other way around? What dominates? Do you feel harmony and balance? Perhaps pungency appears only after a while? Record your results (you can use a 0–7 scale for bitterness and another for pungency). If you are testing an oil with a declared profile, you can compare your score with the professional panel results.

How do we really "perceive" olive oil?

During tasting you use two types of smell:

• Orthonasal smell – the classic one. It's the smell we perceive when sniffing the oil in the glass – from outside, through the nose. We pick up freshness, fruitiness, herbal, apple, tomato, grassy notes, and so on.
• Retronasal smell – aromas reaching the nose "from the inside" when tasting the oil, when aromas from the mouth pass through the throat into the nasal cavity and stimulate the olfactory bulbs. This lets us evaluate the complexity of the aroma, its persistence and the depth of the bouquet. After taking a small amount of oil into the mouth, we perform the "strippaggio" technique – a quick inhalation through the teeth which mixes the oil with air and amplifies its aroma. During this process the retronasal smell is activated.

Together, these two pathways allow tasters to fully evaluate the flavour-aromatic bouquet, capture nuances, and immediately distinguish an outstanding oil from an average one. Both routes combined give the full picture of the olive oil's sensory profile.

If the oil smells or tastes "flat", old, rancid, earthy or metallic – simply don't buy it!

Note! Taste evaluation requires practice – people differ in sensitivity, and expressing impressions in numbers and words can be challenging. Always taste olive oil consciously and compare impressions between samples!

The most common olive oil defects

• Rancid
  Cause: Prolonged storage, fat oxidation due to exposure to air, light or heat. Often found in old or poorly stored oils.
  Description: Smell of old nuts, wax, cardboard or burnt fat.
• Fusty (anaerobic fermentation)
  Cause: Olives stored without air access before pressing, e.g. in sacks or piles.
  Description: Smell of sauerkraut, rotten fruit, mustiness.
• Musty-humid / Earthy
  Cause: Olives were mouldy or contaminated with soil – e.g. collected from the ground after rain.
  Description: Smell of cellar, mushrooms, mustiness.
• Winey-vinegary
  Cause: Alcoholic fermentation of the olives, leading to the formation of acetic acid.
  Description: Smell of fermented wine, apple vinegar, sour apples.
• Metallic
  Cause: Contact of the oil with unsuitable metal parts during pressing or storage.
  Description: Taste and smell resembling metal, copper, aluminium.
• Heated or Burnt
  Cause: Excessive temperatures during malaxation of the olive paste or an improper technological process.
  Description: Taste of cooked vegetables, burnt notes.
• Muddy sediment
  Cause: Prolonged contact of the oil with sediment after decantation.
  Description: Smell of ferment, mud, mustiness.
• Frozen olives
  Cause: Frost damage on the tree before harvest – the cell structures are damaged.
  Description: Watery, washed-out flavour, sometimes bitter.
• Greasy / Petroleum
  Cause: Contamination with machine lubricants or contact with unclean equipment.
  Description: Smell of engine oil, paraffin.
• Rough / Coarse
  Cause: Poor-quality olives, late harvest or a faulty extraction process.
  Description: Unpleasant, aggressive texture, drying on the tongue.

Note: The presence of any of the above defects automatically disqualifies the oil from the "extra virgin" category.

Positive olive oil aromas (fruity notes)

The highest-quality olive oil (extra virgin) should show one of the key attributes: fruitiness. This is a positive feature that can cover a wide range of natural aromatic notes:

• Green olive – fresh smell of raw olives, characteristic of early-harvest oils.
• Ripe olive – a sweeter, milder smell from later-harvest olives.
• Tomato / Tomato leaf – green, slightly herbal notes, typical of Greek and Spanish cultivars.
• Artichoke – fresh, vegetal aroma, often found in oils from Koroneiki or Frantoio cultivars.
• Almond – a delicate, creamy nutty smell, either green or sweet.
• Apple – a sweetish, juicy aroma, often present in well-balanced oils.
• Grass / Freshly cut grass – a green, brisk aroma associated with young, intense olive oil.
• Herbs – notes of basil, oregano, mint or other fresh herbs.
• Banana – a subtle, fruity smell, sometimes linked to riper olives.
• Citrus – aromas of lemon zest, grapefruit, lime – often present in lighter oils.
• Nutty – natural notes resembling hazelnuts or walnuts – not to be confused with the rancid defect.
• Fig leaf – a green, exotic aroma, present in some Mediterranean oils.
• Wild herbs – complex, wild herbal notes, characteristic of organic oils from mountainous areas.
• Green pepper – an intense, peppery aroma, present in fresh oils with high polyphenol content.
• Spicy / Pungent – perceived mainly in the throat, the result of oleocanthal and other phenols.

The presence of these aromas indicates the freshness, quality and complexity of the olive oil. Their intensity and profile depend on the olive variety, harvest timing, climate and pressing method.

Olive oil and its tasting are an extraordinarily complex subject; I hope that I have managed to give you at least a small introduction to its most important and most interesting aspects.

Written by: Tadeusz Gruszczyński,
certified olive oil sommelier.
Copying or using this text without the author's consent is prohibited and may result in legal consequences.