On the importance of a good knead

Puglia olives-coratina?Most modern olive oil producers, no matter where they are in the world, emphasize the importance of a singular process for the production of high-quality oil. That process is best translated as “kneading” the olive paste. In Italy, the machine that does that is the gramola; in California, it’s often called a malaxer from the French word for the machine. Here are two photographs, the one on the left showing an old-fashioned gramola, the one on the right a gramola in a modern mill.

gramola, old-fashioned  gramola - new style






Excuse the quality of the photos, please. This process is devilishly difficult to photograph in the dim lights of the frantoio.

As I hope you can see, the old-fashioned machine is open to the air, with just a steel mesh over it, thus exposing the olive paste to the destructive effects of the environment. The one on the right is completely enclosed, with a thick transparent plastic top protecting the paste.

So what happens here? The olives have been crushed to a dense, dark paste, their bright green color dulled to the hue of cappuccino, hardly an enticement. (But the fresh fragrance permeating the frantoio, the olive mill, more than makes up for the nasty color.)

A century or more ago, this paste would have been spread on woven mats, stacked in a column, and gone straight into the presses to squeeze out the oil. I’ve tried in vain to find out when the gramola was first introduced but it is in modern times a vital part of the process at this post-crushing/pre-extraction phase.

So, the crushed paste is transferred to the gramola’s long enclosed box. The giant screws of the gramola turn very slowly, kneading or malaxing the paste under controlled temperatures (ideally no higher than 27º C) for as much as 30 to 40 minutes, or sometimes even longer. During the process the molecules of oil in the paste start to come together, making it easier to extract the oil in the next and last phase of processing, when a centrifuge extracts oil, on the one hand, and vegetable water, on the other.

What happens to the olive paste in the gramola is as fundamental to quality as it is complex; the effect is to produce vital changes in the chemical and biochemical structure of the oil, changes that have a direct impact on the flavor of the finished oil.

Mirko Sella, an olive oil producer (and wine maker) in the alpine foothills of the Mezzane valley northeast of Verona, makes oil from a local autochthonous cultivar called Grignano. He emphasized to me the importance of the gramola. “Look,” he said, “olive oil is not just fruit juice. Fruit juice you get by a simple mechanical action—you squeeze a lemon and you get lemon juice. But olives that have gone through the gramola on the other hand have their actual chemical structure profoundly modified. It’s a complex process that must be fully understood in order not to commit gross errors”—and produce an oil that is too flat, too bitter, or otherwise defective. Too much time in the gramola will tend to make the oil rancid, too little time will not only yield less oil, but one in which the unappealing bitterness of fresh olives may be all too present.

The Grignano variety that Mirko focuses on is peculiar for its very fruity fragrance and flavor, recalling both citrus and ripe pears—but only if the olives are harvested at a specific moment in the ripening process, neither too green nor too mature, and processed within four hours. I don’t seem to find Mirko’s San Cassiano oil sold in the US but if life carries you to Verona, perhaps for the summer opera festival, you should look for his Monocultivar 100% Grignano San Cassiano. Wrap it carefully and stow it in your checked luggage. It’s perfectly legal to bring back to the US in quantities for personal consumption. And you won’t regret it when you pull the oil out to garnish an autumn feast of crisp greens or meaty wild mushrooms.

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  • Reply John Gizzo September 7, 2015 at 7:00 pm

    Great insight on the kneading process. How can i learn more about the particulars of how to process olive oil and the different variables that a miller would deal with? any books? Thank You!

    • Reply Nancy Harmon Jenkins September 7, 2015 at 7:24 pm

      It depends on what you are looking for, John. If general information–I think my book, Virgin Territory has most of what you would need. If you’re planning to go into the processing of olive oil yourself, you would probably want to consult with The Olive Center at University of California, Davis, which has all the latest information about machines, techniques, etc., as well as info about planting and care of olive trees.

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