I read somewhere -- maybe a James Peterson cookbook? -- that putting olive oil in the blender for more than a few seconds will make it bitter. However, many recipes for hummus, aioli, and other things call for blending olive oil. At times I've felt that making hummus without the oil, and then stirring it in at the end gives a better flavor, but I can't say for sure.
Does anyone have any advice about this?
Well, this is a common confusion between "sour" and "bitter".
The better your olive oil is, the lower its acid value - extra virgin olive oil has the lowest acid value, it is pressed in ways that reduce contact with atmospheric oxygen. Contact with oxygen increases the acid value of olive oil.
Whizzing olive oil in a blender aerates it, and the resultant oxidation increases the acid value, ie it gets more acidic and tastes "sourer".
Lots of people can discern the change, but they don't use the right word to express it ...
Hammering extra virgin olive oil in a blender or food processor allows astringent ("bitter") tasting polyphenol compounds to be detectable by the tongue.
Cook’s Illustrated explained it in their March & April 2009 issue, page 30:
Extra-virgin olive oil contains bitter tasting polyphenols coated by fatty acids, which prevent them from dispersing. If the oil is emulsified in a food processor, these polyphenols get squeezed out and the liquid mix turns bitter.
The Olive Centre suggests that; other factors can also affect the quality of your oil which include air, light, heat, water and too much sediment. Light speeds up the oxidation process which shortens the shelf life of the oil.
Also, there was research carried out which confirmed that dark glass (preferably browner) Antique Green was one of the best ways in which to miminise oxidation compared to other types of packaging.
For further reading here are come suggested links:
Effect of Storage Containers on Olive Oil Quality: https://rirdc.infoservices.com.au/items/09-160
