Search for the finest quality oils to make a stellar vinaigrette

The University of California-Davis headline was a jaw-dropper: "Study Finds 82 Percent of Avocado Oil Rancid or Mixed with Other Oils." Take a moment to let that sink in.

OK.

If you're an avocado oil fan, that is a stunning statistic. Before going any further, to be transparent, the UC-Davis study was funded by a Mexico avocado oil supplier.

UC-Davis tried to test all "major" avocado oil brands, testing 22 oils. They found that 15 of those oils "exhibited signs of being stale" or were "apparently mixed with other oils."

The avocado oils with the highest levels of peroxide (a staleness indicator) were sold in clear bottles.

Lesson Number One: Avoid any avocado oil sold in clear containers.

"Two samples of "extra virgin" and one sample of "refined" avocado oil were nearly 100-percent soybean oil.

Lesson Number Two: oil labels, whether avocado or olive oil, might be ... ahem ... misleading.

UC-Davis found two brands that were not oxidized and pure: Chosen Foods (chosenfoods.com) and Marianne's Avocado Oil (mariannesharvest.com). Both have been refined. One avocado oil that hit a high note with UC/Davis: CalPure California Extra Virgin Avocado Oil - First Cold-Pressed, Unrefined appeared to be available only through Amazon. None of them are inexpensive.

Primal Kitchen (primalkitchen.com), a brand unmentioned by UC/Davis, is my go-to avocado oil. It's sold in a dark green bottle, comes from California and is extra-virgin, first cold-pressed, and unrefined. It's a classic, dark green color, a little cloudy (unrefined) and has a delightful scent and tastes delicious. I'd be surprised if it's not the real deal.

Lesson Number Three: How to tell if your avocado oil is fresh and pure. As consumerlab.com (a testing service website) writes: "fresh, virgin avocado oil tastes grassy, buttery and a little bit like mushrooms." Rancid avocado oil: "... smells stale, sort of like play dough."

The color of the oil can be key. "Virgin avocado oil should be green in color, whereas refined avocado oil is light yellow and almost clear ..." Finally, pay attention to the expiration date on the bottle and only purchase what you can use quickly.

I stopped using commercial, grocery store-bought vegetable oils (really, seed oils) several years ago due to many personal and some scientific reasons. I only use unrefined fruit oils (some organic): olive oil, coconut oil, and avocado oil.

I cook with coconut oil, using olive and avocado oils for salad dressings only. Lately, I'm playing with walnut oil (salad dressing, again) and roasted peanut oil. Roasted peanut oil smells like peanut butter and carries a stronger flavor just as toasted sesame oil does. La Tourangelle makes both.

Yes, I also cook with some animal fats like beef tallow (only from grass-fed, grass-finished beef - a local source), organic lard and organic bacon fat and duck fat (a luxury).

Since most commercial salad dressings are made with soybean oil and ones that aren't are expensive, I make my own dressings. The healthiest dressing I make is a simple vinaigrette. High-quality oil and vinegar make my vinaigrette sing. Anyone can make a vinaigrette (this one's based on one from epicurious.com); here's how.

• Don Mauer welcomes questions, comments and recipe makeover requests. Write to him at don@theleanwizard.com.

Don's Simple Vinaigrette

2 tablespoons finely chopped shallots

2 tablespoons organic white-wine vinegar

1 tablespoon parsley flakes

¼ teaspoon sea salt, or to taste

2 teaspoons Dijon mustard

6 tablespoons extra-virgin avocado oil

Fresh-ground black pepper, to taste

Place a dish towel on the kitchen counter and set a small glass or stainless-steel bowl on it (it keeps the bowl from moving around when whisking). Add the shallots, vinegar, parsley flakes and ¼ teaspoon salt to the bowl and let the mixture stand for 10 minutes.

Whisk in the mustard and then add the oil in a very slow, thin, steady stream, whisking constantly until the dressing is emulsified. Season with additional salt and black pepper. Makes about ½ cup.

Nutrition values per tablespoon: 97 calories (99 percent from fat), 10.6 g fat (1.2 g saturated fat), 0 g carbohydrates (0 net carbs), 0 g sugars, 0 g fiber, 0 g protein, 0 mg cholesterol, 103 mg sodium.