Slick Extra Virgin

At last! A paper reporting the effects of real olive mill based filtration on extra virgin olive oil composition. To date all research on the effects of filtration have been conducted using small lab based simulations.

Bakhouche et al. (2014) Monitoring the moisture reduction and status of bioactive compounds in extra-virgin olive oil over the industrial filtration process. Food Control. 40, 292-299. http://dx.doi.org/10.1016/j.foodcont.2013.12.012

The why?

Filtration is performed to produce perfectly clear oil that most consumers desire. But what are the consequences of filtering?

The how:

45 tonnes of two extra virgin olive oils were filtered through ‘cakes’ of Vitacel_L90 (30 kg, composed of 100% cellulose) and Filtracel_EFC-950 (60 kg, composed of 70% cellulose, 30% lignin) and the change in moisture and polyphenol content was monitored throughout the during the filtration process.

The outcomes:

- Filtering reduced the moisture content by between 20 and 36% depending on how ‘clogged’ the filter was at the time of sampling, and the initial moisture content of the oil.

- (illogically) filtration increased total polyphenols. However most polyphenol types were reduced following filtration particularly the small simple phenolics hydroxytyrosol and tyrosol.

Commentary:

The reduction in moisture content can be attributed to the water binding ability of polysaccharides (of which cellulose is one).

The observation that total polyphenols increased following filtration is ‘bizarre’. Filtration substrates do not contain polyphenols*, so logically, the filter material can either let polyphenols pass through resulting in no change, or adsorb them, which would result in a reduction in polyphenol content. The authors attribute the unexpected increase in polyphenols following filtration to limitations in how the dominant polyphenol class (the secoiridoids) are extracted from the oil prior to being quantified. That is, the illogical increase in polyphenols after filtration is an artifact of the laboratory measurement process.

The other polyphenol classes generally decreased due to filtration. As the filter material became more used, there was a trend for the difference between filtered and non-filtered samples to be reduced. This suggests that the filtration material was absorbing phenolics (because as the filter material has a finite number of binding sites, so as it becomes more used it is less effective in retaining phenolics – so the pass through).

So what can we take out of the study.

1)      Filtration reduces the moisture content of extra virgin olive oil. Practically this is a positive effect as lower moisture means decreased chemical breakdown (hydrolysis) of the fat molecules that make up extra virgin olive oil that lead to free fatty acids (acidity). Lower oil acidity is associated with greater oxidative stability aka shelf life, and higher smoke points.

2)      The effect of filtration on polyphenol content of extra virgin olive oil is still a ‘bit murky’, however there is some evidence that filtration does reduce polyphenols or at least some types of polyphenols.

* The increase in polyphenols was caused mainly by increases in secoiridoid compounds which are found in olive fruit. This rules out the possibility that the filter material inadvertently contained some form of phenolic contaminant which was extracted into the oil during filtration.

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I often get asked whether extra virgin olive oil is more fattening than other edible oils. Given the frequency that the question is posed, I’ll assume that there is some ‘information’ out there somewhere saying that it must be so. Or perhaps it is just a case of people thinking that if extra virgin olive oil is so healthy for you then it must have some downside. Can’t have your cake and eat it too right?

So I searched the peer-reviewed scientific literature to find out the energy (or calorific) values of different edible oils. Two papers provided some relevant data.

Fassinou et al. (2010) measured the energy values for a wide range of edible oils (Figure 1), but unfortunately olive oil was not one of them. However I’ve provided a logical estimate of the energy value of extra virgin olive oil based on the predictive model that they derived (1).

Figure 1: Energy values of various edible oils. Value for extra virgin olive oil is an estimate. See footnote 1.

Sadrameli et al. (2008) determined the energy values of the free fatty acids themselves (actual edible oils comprise 3 fatty acids of various sorts joined together to a glycerol molecule, not as individual free fatty acids). However, these values can presumably be good proxies of the energy values of the edible oils that are rich in a particular fatty acid (oleic acid makes up on average ¾ of the fatty acids in olive oil for example) (Figure 2). However as all edible fats comprise a mixture of fatty acids combined in various combinations in groups of three, this data is at best an estimate of the energy values of real edible oils.

Figure 2: Energy values of different fatty acids. Examples of edible fats that have high proportions of that fatty acid are given in parenthesis.

So what’s the conclusion? There is no practical difference in the energy values of the different edible oils.

OK, these results do not consider that our bodies may absorb one type of fat differently from another. Some have suggested that we absorb short chain fatty acids such as those found in coconut oil differently. You can read more about the good, the bad and the ugly of this possibility elsewhere in this blog (search for coconut oil in the search box to the right), but based purely on the maximum potential of each fat to contribute to our daily energy intake, there is little evidence of any practical differences between edible oils when it comes to their energy quotient (2).

References

Fassinou, W.F., Sako, A., Fofana, A., Koua, K.B. and Toure, S. (2010) Fatty acids composition as a means to estimate the high heating value (HHV) of vegetable oils and biodiesel fuels. Energy, 35, 4949-4954. doi:10.1016/j.energy.2010.08.030

Sadrameli, S.M., Seames, W. and Mann, M. (2008) Prediction of higher heating values for saturated fatty acids from their physical properties. Fuel, 87, 1776-1780. doi:10.1016/j.fuel.2007.10.020

Footnotes:

(1) The energy value can be predicted from the ‘carbon number’ of the oil. The carbon number is the average carbon chain length of the fatty acids that comprise the oil. In olive oil the carbon number averages 17.5 (based on the fatty acid profiles of 500+ extra virgin olive oils reported by Mailer and Ayrton 2008). The energy value of the ‘typical’ extra virgin olive was then estimated using the predictive model derived by Fassinou et al. (2010)..

(2) To save you scrambling for your abacuses paleo people, coconut oil has on average 3% lower energy value compared with the other oils, which is due to the lower average carbon number of the predominant fatty acids in coconut oil. 3% less energy but 90% less antioxidants. Take your pick.

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What is Extra Virgin Olive Oil?

The ‘oily’ olive fruit juice extracted from fresh olives using a mechanical process which does not involve the application of excessive heat, additives or solvents.

Should I only buy first cold pressed oil?

Most extra virgin olive oil is produced by spinning the lighter oil away from the other heavier components of the olive such as water and olive matter using a centrifuge. So the term ‘cold pressed’ is redundant.

What’s the difference between extra virgin olive oil and other types of olive oil?

Extra virgin olive oil is a whole, unprocessed food and therefore contains higher amounts of healthy antioxidants. Conversely, ‘light’, ‘pure’, ‘olive oil’ and pomace oils are highly processed products.

Is ‘Pure’ olive oil better than Extra Virgin Olive Oil?

No. The word ‘Pure’ (together with ‘Light’) are purely marketing terms applied to refined olive oil. Pure sounds better than refined.

Do ‘light’ olive oils contain fewer calories than Extra Virgin Olive Oil?

No. All olive oils (and indeed all edible oils) have the same energy values.

This oil is bitter and peppery. Is it ok?

The bitterness and pepperyness indicates that the oil contains healthful antioxidants.. These characters complement the taste of strongly flavoured foods.

Is eating Extra Virgin Olive Oil good for my health?

EVOO’s contain significantly higher levels of monounsaturated fats and antioxidants than any other oil. These attributes are sought after by the health conscious.

Does the colour of olive oil indicate quality?

No. High quality extra virgin olive oils can appear emerald green through to golden yellow.

Where should I store Extra Virgin Olive Oil?

They should be stored in a cool dark place. For longer term storage where oils are used infrequently, refrigeration is a good option.

How long does Extra Virgin Olive Oil last?

They are best consumed young as fresh flavours and healthful polyphenols decline over time.  So when the new season oils are released, buy them.

I’ve heard that you can’t cook with Extra Virgin Olive Oil as its smoke point is too low. Is this true?

The temperature at which good quality (low acidity) extra virgin olive oil begins to smoke is significantly higher than what is needed to fry food (180C). So you can fry in EVOO.

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Figure 1: Consolidated results of Choice supermarket EVOO testing 2000, 2003, 2007 and 2010

The vast majority of extra virgin olive oil (EVOO) sold and eaten throughout the world is purchased in a supermarket, so independent reviews of the quality of extra virgin olive oils in this market are invaluable.

The Australian Consumer Association (ACA) does such a thing. The ACA is a respected not for profit and fiercely independent organisation that Australian consumers ‘go to’ when they want reliable and trustworthy advice on what to buy, and what to look for when buying it. Thankfully for Australian extra virgin olive oil consumers, the importance of this product hasn’t slipped by the ACA as they have reviewed EVOO’s sold in Australian supermarkets every four years or so since 2000.

The ACA samples extra virgin olive oils from Australian supermarket shelves and asks a panel of experienced extra virgin olive oil tasters to assess their quality. The selected oils represent most of the major nationally available brands, but also include some that are only available in smaller independent supermarkets. The tastings are conducted totally blind i.e. no information about the oil is revealed to the tasters. The tasters are drawn from a variety of industry sectors (growers, processors, chefs and (mostly) tasters trained using International Olive Council tasting protocols), None of the tasters have any association with the products being evaluated. The results are published in the ACA magazine “Choice”.

I have taken the liberty of trawling through past issues reporting olive oil reports and have summarised the results in the table below. I have not published the brand names of the oils, as this is the domain of the ACA. Interested readers can go here to find the identity of the 2010 oils, and details as to why they were scored as they were. However, in the table that I have provided which summarises the results of 4 ACA tastings since 2000 (Table 1), I have given each brand a unique letter (if it was available nationally across at least 3 of the 4 tastings conducted) These generally represent the major selling brands in Australia.

In the early tastings (2000 and 2003) the oils were only classified into broad categories (very good, above average, ok, poor etc). In later tastings (2007 and 2010) the oils were scored for quality using the 20 point Australian Show judging system, but were not categorised in the same way as had been done previously. In order to create a consistent ‘quality time line’ spanning the 14 years, I logically equated the generally accepted interpretations of the show judging scores to the categories used in earlier tastings

Here is how I did it.

Score/20        Accepted interpretation                                                 Assigned category

less than 10    The oil has a recognized taste defect                          poor/unacceptable

10.0 – 12.5      No defects but is below average (no medal)              marginal/ok

13.0 – 14.5      Above average (bronze medal in AUS competition)   above average

15.0 – 16.5      Very good (silver medal in AUS competition)               very good

The consolidated results of the Choice tastings from 2000-2010 are shown at the top of the blog. Notes: SMG = supermarket generic i.e home or white label brand. Olive oils within the same category (2003 and 2007), or allocated the same score (2007 and 2010) are listed in the table in alphabetical order.

The quality time-line by country of origin goes like this…

The ratings assigned to each of the quality categories which were then used to generate the average quality ratings by country of origin were:

Very Good = 4, Good/Above Average = 3, OK/Average = 2, Borderline/Below Average = 1, Unacceptable/Poor = 0

When averaged, we can create a time line of quality by country of origin …Dah Daaaah…

In case you were wondering, In 2007 and 2010 the oils were given a quality score, so an average quality by country of origin can be calculated directly. They are:

*Greece average 11.9 (5 oils)

So What Do the Results of the Tastings Say?

-  Extra virgin olive oils made in Australia were rated more highly than those labelled as Spanish and (particularly) those labelled as Italian. This was true of all four tastings spanning over a decade.

-  The average quality of Australian olive oils sampled showed an upward trend.

-  The average Australian made supermarket EVOO sampled by Choice and sold in 2010 were of a ‘bronze medal’ standard which In lay-mans terms should be interpreted as “a sound defect free olive oil that has distinct olive characters”.

-  EVOO’s sampled by Choice that were of Spanish origin* were on average ‘marginal’. Scores of around 10 suggest that the oil were marginal when it came to defects but would probably not offend the average supermarket buyer.

-  EVOO’s sampled by Choice that were of Italian origin* were on average of poor quality and on average fell in the scoring range reserved for oils with clear and distinct defects.

Some general points regarding the tastings

In the case where an olive oil was considered to have been of poor/unacceptable quality, a second bottle purchased from another supermarket (sometimes from another State) was re-tasted. The highest of the two ratings were published (and are given here).

A small number of Greek oils were sampled – 2 or 3 in each year. Given the small sample size they have not been included in the tables or figures, but I have provided their assessments in footnotes for completeness.

I was one of the tasters in 2000, 2003 and 2007.

* Extra virgin olive oils imported from the EU into Australia and the US are often labelled as product of the country where they are blended and bottled rather than made. In particular, hundreds of thousands of tonnes of Spanish and North African olive oil is blended and bottled in Italy each year and are sold to the United States and Australia (and probably all other countries outside the EU) as ‘Product of Italy’. Many of the so called Product of Italy oils sold in Australian supermarkets have the distinctive taste and smell of the olive variety Picual…. Picual is not grown in Italy. Transporting olive oil from Spain and Greece and North Africa to Italy and packaging it there allows the ‘Product of Italy’ claim to be made outside the EU. This is a license to print money as on average oils with ‘Product of Italy’ claims attract higher prices than when labelled as product of Spain or Tunisia. So make no mistake. Very few supermarket oils sold outside the EU that are labelled as product of Italy or suggest that they are a product of Italy actually are what they claim. In recent years, some of the brands are more accurately stating on their label that they contain blends of Italian olive oils and those from other countries, blended in Italy. The % breakdown by country is not given, but is very likely that the majority of oils in the blend are not grown in Italy given that Italians consume more olive oil than Italy produces. I recommend that you ring the information line of the producer to find out more about the actual origin of the oils they sell.

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Note: The copyright to this cartoon is solely held by the artist.

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Each year I attend the Australian National Extra Virgin Olive Oil Conference hosted by the Australian Olive Association, where Tim Smith, Marketing Manager for Australia’s largest extra virgin olive oil producer, Boundary Bend Limited (known to most by their brand, Cobram Estate), usually presents an update of the trends in the Australian olive oil market.

His informative presentations draw on a significant amount of data that either isn’t either publicly available (i.e supermarket sales data from private market research firms), or data that takes quite a bit of time compile such as imports and exports. I always look forward to hearing about how Australian producers are faring in their quest to gain greater consumer acceptance, and in wrestling a greater share of the domestic olive oil market from their powerful EU competitors.

So during his presentation given in November 2013 in Hobart, Tasmania, I scribbled down as many of the interesting factoids that I could with the view to sharing what I found particularly interesting.

The message? It IS possible for New World producers to wrest market share from the powerful EU packagers, if they efficiently produce consistently high quality extra virgin olive oil at a competitive price.

Having said that, the business of selling olive oil is a game of thrust, parry and riposte. Traditionally market share has been wrested back by undercutting the competition, which is much easier to do when your commercial operations are propped up by Governments (aka taxpayers) via payment of production and storage subsidies, and import tariffs are levied on the competition. Australia has no import duties/tarriffs on olive oil entering from the EU (or anywhere else), and, unlike the EU, Australian producers do not receive production or storage subsidies from taxpayers. These free trade policies (which I support by the way) unfortunately leave the progress made by local producers vulnerable to being wound back by those not subject to the same level playing field.

I guess time will tell, but I’m confident that quality at a competitive price will continue to put good old fashioned competitive pressure on those who thought they would never be challenged.

You can view the presentation in full screen mode at here (use the arrow keys at the bottom to navigate).

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About a year ago an American producer and friend of mine said that he had heard from someone who had attended a conference somewhere that yeasts can survive for a long time in bottled extra virgin olive oil and that their activity is detrimental to the oil quality.

I was sceptical. Once bottled, extra virgin olive oil it is thought to be one of the most microbiologically stable foods. I’m pretty sure that if you took your grandmothers olive oil out of her manky pharmaceutical studded cabinet, that was left to her by her grandmother, you could chug down the whole lot of it and not get sick. You may re-acquire a taste for fast food, but you’ll wake up the next day feeling ok.

So when I recently came across the journal article titled

Effects of some oil-born yeasts on the sensory characteristics of Italian virgin olive oil during its storage (Zullo et al. 2013) I thought, ah there is the likely source of my American mates ‘Chinese whisper’ information.

So do olive oil producers really have get yeast counts done on the bottled oil to ensure that their oil doesn’t degrade faster than usual? I have to say that have always treated research reporting potential ‘problems’ that no one has noticed before, even after making the stuff for a couple of thousand years. But with an open mind, I looked at the ins and outs of the very detailed paper closely.

The researchers swabbed some EVOO’s, and ‘plated up’ what they found into a warm lagoon of yeasty heaven which allowed them to grow up enough yeast cells to inoculate a perfectly good extra virgin olive oil to assess the effects of yeast on oil quality during 4 months of bottle storage.

But keep in mind that the number of yeasts found in olive oil is pretty low probably due to the fact that the relatively waterless environment of an olive oil isn’t their favourite hang-out. However, after culturing them up in the laboratory, they added them back at a rate of (wait for it), 25gms of yeast for every 100L of EVOO. That is about the same amount of yeast that winemakers used when they ferment grape juice into wine. In laymans terms ‘bucket loads’. To put the amount they used into an olive oil perspective, they estimated that they added around 100,000 yeast cells to every 1ml of oil. Compare that to the 1,000 odd yeast cells per ml that are naturally found in olive oil (based on a survey of 14 commercial olive oils from the Liguria and Central Italy, Zullo et al. 2010).

So what effect did adding 100x the typical number of yeast to an olive oil and leaving it for 4 months have?

Probably not surprisingly, the yeasts were shown by the researchers to produce all sorts of evocative (to a microbiologist anyway) enzymatic activity – Peroxidase, tyrosinase, phenoloxidase, and b-glucosidase, which could potentially degrade olive oil and affect its quality. But we all have ‘potential’ don’t we?

Here are the effects that matter. The effects on the chemistry and taste ….
Table 1: The effect* of inoculating with these large amounts of yeast and then storing the oil plus yeast for 4 months.

*The researchers looked at the effects of half a dozen yeast types. I averaged their effects and presented them with changes to the same oil that had not been yeast inoculated and stored for the same length of time.
^Approximate value as the raw data was read off a figure, but it gives you an idea.

They also found that yeast inoculation modified the profile of aroma compounds, with yeasty oils having lower amounts of the grassy tasting C6 compounds. Interestingly though, many other compounds that are normally associated with poor tasting olive oil (C7, C8 and C9’s) did not increase – indeed many of them decreased in the presence of yeast.

There are a few ways of looking at these results, including that you could add yeast to your olive oil to improve its oxidative stability! Lower peroxide values and lower secondary oxidation values are good things right? Well that is what the data suggests. Others would look at the results and emphasise that polyphenols were reduced by 10%, and the oil was less fruity and some yeast produced a faint muddy aroma. But, despite the fact that the researchers appeared to try to use experimental extremes to induce an effect by all manner of yeast types, they barely dented the quality of olive oil.

Where an extra virgin olive oil is bottled immediately after extraction, and is still ‘murky’, then maybe, just maybe these results may apply. However, oils of this type are meant to be consumed immediately as they have a high moisture content and contain relatively large amounts of vegetative solids. It is arguable that they would probably go muddy even without any yeasty action, as keeping vegetable solids in a highly anaerobic (airless) environment will most likely do that anyway.

So hopefully we won’t be seeing tests for yeast cell counts any time soon. We have enough tests already.

Zullo, B.A., Cioccia, G. and Ciafardini, G. (2013) Effects of some oil-born yeasts on the sensory characteristics of Italian virgin olive oil during its storage. Food Microbiology, 36, 70-78.

Zullo, B.A., Cioccia, G. and Ciafardini, G. (2010) Distribution of dimorphic yeast species in commercial extra virgin olive oil. Food Microbiology, 27, 1035-1042.

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To many people, the characteristic smell exuded by the linseed oil that their grandfather kept in his mancave for 35 years IS the aroma of olive oil. For them olive oil is supposed to smell like that, and it is exactly how they like it. I have always considered these people ‘misguided’. Surely, they must have learned to like rancidity. Perhaps a great-aunt from Omaha or Boise led them astray in their early childhood by force feeding them stuff out of the medicine cabinet. You know, the manky stuff with the yellowed label that needed carbon dating to validate the century in which it were made. But recent research using mice (Nankano et al. 2012) suggests that unsavory bullying from an uninformed, stodgey great-aunt might not be necessary to appreciate the delights of rancidity after all.

So here is how it went..

To provide a base-line, mice were presented with two bottles of the same non-oxidised olive oil in their feeding cage for three weeks. The amount consumed from each bottle was the same showing that the mice didn’t have a favourite restaurant strip.

But then one of the feeding bottles of fresh oil was replaced with another containing oxidised olive oil (left in a hot place in an open bottle for 3 weeks). The mice given the choice, consumed 10 times more of the oxidised oil than the fresh oil. The experiment was repeated using a heated refined olive oil. Same result – the mice chose to eat a lot more rancid oil than fresh oil.

Furthermore, the more the oil was oxidised (they made up blends of fresh and oxidised), the greater the preference for it. Mice that were anosmic (had no sense of smell) didn’t prefer one oil type over another suggesting that the aroma and flavour of the olive oil was the driving factor in preference.

Does this mean that rancid oil is the default for preference, and that appreciating fresh olive oil is a learned response? But leaving this important philosophical aside what I really want answered is – how the hell did the researchers identify anosmic mice (the ones without a sense of smell) from the non-anosmic mice? Did they put them under a bed doona and record which ones tried to escape?

Source: Nakano et al. (2012) Effects of aroma components from oxidised olive oil on preference. Bioscience, Biotechnology and Biochemistry. 77, 1166-1170.

You can read the article here: https://www.jstage.jst.go.jp/article/bbb/77/6/77_120861/_article

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a)      Mechanical processing includes methods that do not use solvents or excessive heat to extract the oil.  These methods include centrifugation and (now, rarely) pressing.

b)      Pomace is the mix of skins and crushed olive seeds left over after most of the olive oil and water have been mechanically extracted from the olive paste.

c)      Usually hexane is the solvent used.

d)     Refining involves a number of steps which involve the addition of strong acids and bases, and the application of processes such as chilling, washing, centrifugation, filtration and deodorisation.

e)      Pure olive oil is no ‘purer’ than any other olive oil. ‘Light’ olive oil does not have fewer calories than any other oil. The term ‘light’ refers to its lighter colour, aroma and flavour – a result of the oil having been refined.

More information on the difference between olive oil types can be found here

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