Can you store extra virgin olive oil in the fridge?
admin | February 23, 2010Yes you can! And yes you should….
One of my twitter followers/friends recently asked if extra virgin olive oil can be safely stored in the fridge. They heard somewhere that “the shelf life is reduced, and valuable polyphenols are lost during refrigeration”.
While I have heard this before I couldn’t recall seeing anything solid. However, on face value this seemed rather strange as we generally refrigerate foods so as to slow down oxidation rather than to speed it up.
After a thorough search I found that somewhat surprisingly, that only two scientific papers have reported the effect of refrigerating extra virgin olive oils. One was probably the one that my twitter friend was referring to. I read both the abstract (the summary which is freely available) and the whole paper (which is not). I’m not surprised that the abstract led many to believe that refrigeration was detrimental to maintaining EVOO quality. However on close inspection the actual results clearly suggested otherwise.
In this work, a single EVOO was stored in the fridge at below its melting point 3C, and at 25, 40 and 60C (Calligaris et al. 2006). The oxidative state of the oils were monitored over a 7 month period using a well known measure called peroxide value. They found that this EVOO when stored at 3C had almost exactly the same peroxide value over the entire 7 month period as when it was stored at room temperature (25C). Now as scientists this must have seemed a bit unusual as one would expect that the oil stored at the cooler temperature would have a lower peroxide value. Based on this they surmised that: “below the melting point , the oxidation rate was found to be higher than expected”.
‘Higher than expected’ yes, but the oxidation rate of refrigerated oil was still about the same or lower than when stored at room temperature. Unfortunately, this practically important last little bit didn’t make it into the summary. Here are the results read from their paper (Figure 4). You can see for yourself.
Peroxide Value of an EVOO stored at 4 temps over 200 days | ||||
Temp oC | Day 25 | Day 50 | Day 100 | Day 200 |
3 | 11 | 11 | 15 | 19 |
25 | 11 | 12 | 15 | 21 |
40 | 17 | 26 | – | – |
60 | 23 | 42 | – | – |
So despite what appeared to be reported in the summary, storing oils in the fridge was the best option of all those studied.
Ok some would be thinking… so it appears that storing the oil at room temperature is just as good as stroring in the fridge so I’ll just leave it in my pantry. Well maybe, but then again maybe not. The polyphenol level of the oil used in the study was a massive 772 mg/kg. This is around 3 times the average polyphenol level of your typical EVOO (Gawel and Rogers 2009). Polyphenols are antioxidants, so in this particular case, the polyphenols are providing a massive amount of protection against oxidation. That particular oil probably could have withstood a nuclear test blast in the Nevada desert in 1952 and still be edible today. Whether an EVOO with a more typical polyphenol level of around 200-250mg/kg would have stood up that well at room temperature is debatable. That’s the risk of doing research using a single oil-particularly an odd one!
The abstract also reported “a decrease in polyphenols in the liquid phase” upon refrigeration. Anyone that read this would naturally think that the polyphenols disappeared as a result of refrigeration. It was an unfortunate use of terminology. What the authors were referring, was not the oil in its entirety after being thawed, but only the little bit that was still liquid at 3C. The polyphenol level of the entire oil after thawing wasn’t reported, but my guess is that it would be pretty similar to or higher than the oil stored at 25C (oils with lower peroxide values tend to keep their polyphenols longer). Ok that low phenolic liquid bit would be more prone to oxidation while sitting in your fridge, but the fact that it only made up around 20% of the volume and is being held at 3C has to be taken into consideration.
The second study on cold storage of EVOO’s showed similar benefits (Prenzler et al. 2007). Here a relatively low polyphenol EVOO was stored in 100ml bottles at room temperature, and the same oil in the fridge at 1oC. After twelve months, the polyhenol reading of the room temperature oil was 148 mg/kg. The same oil stored in the fridge had a polyphenol level of 185 mg/kg. Yes that’s right, refrigeration helped retain polyphenols, not destroy them. In addition the free fatty acidity, and all measures of oil oxidation (peroxide value, K232 and K270) were lower for the oil stored in the fridge. Sure the authors did correctly report that the oil did age somewhat when stored in the fridge i.e. when compared to the oil when new. You wouldn’t expect any different unless the researchers used a cryogenic device like that in the Jupiter II in ‘Lost in Space’. But the important point is that the fridge stored oil did better than the room temperature stored oil on all counts of quality.
There are two relatively small issues in storing oils in the fridge. Firstly, once opened and resealed, the bottle has the potential to trap humidified air which may condense on the inside of the bottle which in turn has the potential to cause the oil to tire. This is probably only an issue if you constantly take the oil out of the fridge over a long period of time, and then again I think that the benefits of slower oxidation outweigh the potential costs. Secondly, very occasionally some oils refuse to thaw completely when taken out of the fridge. This is because some of the natural waxes found in EVOO just refuse to go back into solution. Don’t be concerned. The few chunky bits are harmless and will definitely disappear if you heat up the oil when cooking. I’ve only seen two cases of this in thousands of bottles so I wouldn’t loose any sleep over it.
For good measure here are the papers I’ve mentioned and yes, the blatant yet obligatory self citation.
Calligaris, S., Sovrano, S., Manzocco, L. and Nicoli, M.C. (2006) Influence of crystallization on the oxidative stability of extra virgin olive oil. Journal of Agricultural and Food Chemistry, 54, 529-535.
Gawel, R. and Rogers, D.A.G. (2009) The relationship between the total phenol concentration of virgin olive oil and their style as determined by their producers. Grasas y Aceites, 60, 134-138.
http://grasasyaceites.revistas.csic.es/index.php/grasasyaceites/article/view/560/574
Prenzler, P., Robards, K. and Bedgood, D. (2007) Quality enhancements of Australian extra virgin olive oils. Rural Research and Development Corporation Report.
https://rirdc.infoservices.com.au/downloads/06-135.pdf
Hi,
What an amazing resource this blog is — thank you so much!
Questions on this post:
– what does it mean for an olive oil to ‘tire’? I actually keep my EVOO in the fridge all the time, which usually necessitates letting it partially thaw for ~10-20 mins into a very thick but pourable goo. Is this a worse idea than keeping it at room temp? (I am asking only in terms of polyphenols and peroxidation — I like the flavor of EVOO, but am not a true connoisseur thereof).
– Can you disclose which brands of EVOO that you tested had which polyphenol counts?
Thanks!
‘Tiring’ means that the oil is in the early stages of rancidity. For me, oils start to taste fatty and leave a residue in your mouth not unlike if you sucked on the fat of a lamb loin chop. But that’s a personal interpretation.
Re the oil you mentioned. This info was reported in the scientific journal which I cited at the bottom of the blog. It is unusual for the commercial identity of the product to be given. You would have to email the corresponding author of the article to find out what the oil was.
Hi again Richard,
You replied, re my request about EVOO polyphenol content, that “This info was reported in the scientific journal which I cited at the bottom of the blog. … You would have to email the corresponding author of the article to find out what the oil was.”
But you *are* the corresponding author 😉 . The data for which I’m asking is: “The polyphenol level of the oil used in the study was a massive 772 mg/kg. This is around 3 times the average polyphenol level of your typical EVOO (Gawel and Rogers 2009). ” I downloaded this article, from teh link you helpfully provide in your citation list; brands vs polyphenol content are not given.
Sorry for being unclear, and thanks again.
Hi Michael
ok I can see where you are coming from. To clarify, the citation Gawel and Rogers was put in to justify the statement that 772mg/kg is 3x a typical polyphenol level in an EVOO. We analysed the polyphenol levels of 560 different oils submitted to Australian EVOO competitions to come up with an average of around 250mg/kg. The oil with the pphenol of 772mg/kg was the one used by Calligaris et al. (2006). It’s composition was given in Table 1 of their paper. I have no idea where it came from or what variety it was. No details were given. Hope this helps.
Yup, I understood that (but thanks for explicating). What I’m asking is not about that one, super-high-polyphenol brand (I’ll follow up with the Calligaris paper folks, as you suggest); I’m asking about those 560 other oils that you and Deborah Rogers had tested, which would obviously give a much wider range of price and polyphenol options. (I take it you didn’t do the additional testing to determine their oleocanthal content, ja?).
If you can indulge me, I have an unrelated question: I just saw a bottle of olive oil that says it was pressed in late 2009, from the Fall 2008 fruit harvest. Is it normal for olives to be kept that long after harvesting before pressing? Is this required for some kind of further ripening or maturation, or is it just typical practice, or is it (as I would, in my ignorance, assume) a good sign that the fruits will be so old as to go into the press already somewhat peroxidized and denuded of polyphenols?
Thanks again!
Hey thanks for this information!
Do you know where I could find studies on the amount of olive oil that is refrigerated versus not refrigerated in a domestic setting?
Cheers!
Dom
Hi Dom
No I don’t think anyone has ever done a survey like that. In fact, very little information is out there on how and why people use EVOO, let alone how they store them. But my guess to your question is “very few”. The fact that olive oil tends to partially solidify in the fridge has led many to believe that its somehow bad for the oil which is incorrect (unless the chill and thaw are very frequent).
Richard G.
Hi again Richard,
After my clarification, above, that thread of discussion was dropped. It occurs to me that the information might be confidential or proprietary. If this is the case, or if you otherwise really aren’t in a position to answer, or prefer not to, I’ll cease being a pest.
I would, however, appreciate any information you might be able to disclose on this subject. If, for instance, the issue is that you don’t want to offend producers that scored low, could you cite a few examples (top 10s, or maybe top quartiles, or oils above some minimum threshold) — possibly a few from supermarket brands as well as boutique producers? I find it astonishingly difficult to get such information, and from both scientific reports and a few companies that do have information, I know that you can’t go by cultivar and peroxide levels alone: eg, the producers of two otherwise high-quality Koroneikis told me that their oils contained ≤ 150 ppm, when one might well have expected >350.
Thanks for whatever you can share. I really value your blog and your willingness to share your knowledge and expertise, but again, if you just can’t say, please tell me so and I’ll respectfully stop bugging you.