Nothing holds more promise than smooth olives on the branch, framed by delicate gray-green foliage. But that plump and pretty fruit will make your eyes wince and mouth pucker if it's sampled raw. The raw olive contains bitter oleuropein.
To become tasty, the olive needs to shed much of that bitter tannin through a process known as curing. Over the millennia, people have come up with various curing techniques, designed to bring out different flavors and textures.
A lye bath is the quickest way of breaking down the chemical bond between oleuropein and the olive’s natural sugars. With more mature olives, the leaching process can take just a single day. The rinsing phase takes longer, at least several days. With repeated soaks and draining, the olives are cleansed of all trace of the caustic lye solution. The rinses also remove the leached out tannins.
A lye-cured olive is likely to taste mellow. But the ultimate outcome depends on the type of olive, the degree of ripeness at harvest and the post-curing method, which prepares the olive for storage. The final processing may employ brine, herbs and/or olive oil.
Salt-water baths are at the other end of the time spectrum. At minimum, brine curing takes a month –and only if the olives are cracked ahead of time, so the salt water has immediate access to the inner flesh. For whole green olives, the process can take well over six months.
Every processor’s recipe is different. Some use a weak solution of one part salt to 16 parts water, while others double the concentration. The olives often take their saline baths in airtight conditions. Some family recipes, however, recommend using an open tub of salt water. Another variable is how often the water gets changed.
The brine solution promotes fermentation, changing the olive’s inherent sugars into lactic and acetic acid. Brine curing downplays bitterness while bringing out a sour tang.
Salt can also work without water. This method, which is faster than the briny baths, takes advantage of simple osmosis. It works to best effect on oil-rich, dark olives. Generously coated in salt, the olives go into a container that permits drainage of the bitter inner juices.
The container is typically topped off with more salt.
Over several weeks, the olives get rotated to ensure adequate salt distribution. The cured olives are then removed and air dried overnight. Olives cured in this way will be wrinkled and salty, with a touch of bitterness.
One passive way of reducing oleuropein starts with nothing more exotic than water and cracked olives. For 3-4 weeks, they soak in a succession of baths -- with regular changes of water to remove not only the bitter juices, but also the mold that inevitably forms.
Water-cured olives have more than a touch of bitterness. More susceptible to spoilage, they typically go through a “finishing bath” in such antibacterial solutions as vinegar or brine.