Avoiding poor-quality olive oil

As you may have seen in recent news, olive oil can be unreliable in quality and often fail quality checks. So I'm summarizing information from olive oil connoisseurs to help you choose quality oils:

Quick brand suggestions

I'm basing these suggestions on olive oil connoisseur Tom Mueller's more-detailed "supermarket picks". He has tasted them all, and believes tasting them is a better guide than chemical analyses.

When shopping at	Look for
King Soopers / Kroger, Raleys Supermarkets, QFC	Cobram Estate Extra Virgin Olive Oil
Costco	Kirkland Toscano Extra Virgin Olive Oil Make sure to get the Toscano oil, the larger non-Toscano plastic container is poorly-reviewed.
Whole Foods	Whole Foods 100% Californian Extra Virgin Olive Oil Make sure to get the Californian oil, other varieties have failed taste and chemical analysis tests.
Other Stores / Online Shopping	See Tom's full list of "supermarket picks", or his high quality Great Olive Oils list, arranged by country. Also see Steph Fiou's suggestion of Queen Creek Olive Mill with online ordering available.

Chemical analyses of olive oils

Here are the UC Davis Olive Center reports that sparked most of the news about "tainted" olive oils:

• 2010 report
  • Brands with problems: Filippo Berio, Bertolli, Pompeian, Colavita, Star, Carapelli, Newmans Own Organics, Mezzetta, Mazola, Rachael Ray, Kirkland Organic (only slightly out of range on pyropheophytins on one sample), Great Value 100% (only knocked down to virgin on one sample by a taste test), Safeway Select, 365 100% Italian, Bariani (only knocked down to virgin on one sample by a taste test).
  • Brands with no problems: Corto Olive, California Olive Ranch, McEvoy Ranch Organic, Lucero (Ascolano).
• 2011 report of brands sold in California
  • All of the brands they tested (California Olive Ranch, Cobram Estate, Lucini, Colavita, Star, Bertolli, Filippo Berio, and Pompeian) had some type of problem now that a more sensitive German/Australian chemical testing was used.

I noticed an interesting conclusion in the first report: "If any of the samples were adulterated, it is most likely that the adulterant was refined olive oil rather than refined nut, seed, or vegetable oils. Unless the adulteration levels were very small, the failed samples would not have met the IOC/USDA standards for fatty acid profile and sterol profile if adulterated with refined nut, seed, or vegetable oils." That's contrary to the impression given by news reports on the subject, and at least relieves my concerns that high omega-6 oils might be frequently used.

Rules of thumb for selecting your own olive oils

Freshness

• Prefer brands that list a harvest date in addition to a "best by" date, ideally with a harvest date that's less than 18 months old. Many manufacturers want to obscure the age of their olive oil by leaving out harvesting and bottling dates. For example, my local King Soopers (Kroger) store stocks around 30 brands of olive oil, only two of which shared their harvest dates.
• If there's no harvest date available, prefer those with a "best by" at least a year the future. My local store had oils that had already passed their "best by" date.

Production

• Prefer extra virgin olive oil to fino, pomace, or virgin oil.
• Prefer olive oils that specifically state they are "cold-pressed" / "first cold-pressed" (preventing degradation and nutrient loss).

Geographical origin

• California oils are probably a good default choice if you don't have a preference.

Certifications to look for

• California Olive Oil Council (list of certified oils and certification standards information available).
• North American Olive Oil Association (list of certified oils available, see the right-hand column for brands).
• Extra Virgin Alliance (list of certified oils available).
• USDA Olive Oil Quality Monitoring Program (I haven't found any brands other than Pompeian participating in this program).

Container

• Prefer glass containers to plastic containers (preventing air permeability and leaching problems).
• Prefer darkened (amber or green) containers (protecting the oil from light).

Don't worry about:

• Oil color: color does not indicate the quality of the oil, and can be manipulated by the manufacturer.
• Filtered/unfiltered: you can choose this based on your taste preference (unfiltered will have more fruit particles in it, giving a stronger taste). I've read contradictory conclusions on which form has a longer shelf life.
• Fruit intensity: you can choose this based on your taste preference (on a scale of delicate, medium, or robust).
• Identifying aldurated oils by refrigeration: the UC Davis Olive Oil Center concludes that this is ineffective.

Storage and expiration

The ideal storage for olive oil is a cool and dark place. The Olive Oil Source concludes that 50°F is an ideal storage temperature to avoid clouding the oil, but that lower temperatures do not harm it. That makes me conclude that most people should just store their oil in the fridge if they don't mind some thawing time and clouding.

Selena Wang of the UC Davis Olive Center says, "we usually see that oil is no longer good after four to six months after opening." That suggests to me a strategy of buying smaller bottles throughout the year instead of buying in bulk.

Detailed olive oil information sources

• Tom Mueller, the olive oil connoisseur I mentioned above, has an entire site of useful information about olive oil, and even a very well-reviewed book about it.
• UC Davis has a detailed report on the pros and cons of different container types.
• Let There Be Bite attended the UC Davis olive oil tasting class and shares olive oil information and shopping tips.