ASK YOUR SCIENCE TEACHER: Green vs. black olives

ASK YOUR SCIENCE TEACHER: Green vs. black olives

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This week’s question was asked by a city resident.

QUESTION: Why are green olives stored in glass jars and black olives stored in cans?

ANSWER: Olives all start out as the same fruit. Their color is determined by how they are processed.

What about black olives? The harvested olives are put in a water and lye solution and oxygen is piped in. After two days the lye is washed away. The lye penetrates the olive down to the pit.

After the lye is discarded, a brine solution is prepared and ferrous gluconate is added. Ferrous gluconate is a water-soluble iron salt of gluconic acid. Gluconic acid is found naturally in fruits, vegetables wine, and honey. The combination of added oxygen and gluconic acid gives the olives that black color.

The olives are ready to go in a can. Canned food has to be cooked to kill the bacteria. The cooking also takes out a lot of the bitter stuff, which is why canned black olives are so sweet tasting. Cooking reduces the chances of botulism. Botulism had wiped out the California olive crop in 1919. Black olives are cooked and cooked directly in the can to save time and money.

That ferrous gluconate cited above is an iron supplement often used to treat anemia. Common brand names are Ferralet, Simron and Fergon. Some people may have an allergic reaction to ferrous gluconate. Symptoms include hives, difficulty in breathing and mouth, facial and throat swelling. About the same symptoms one gets when the tax bill arrives!

Green olives are harvested before they are ripe. Green olives are packed in brine-filled jars and cured in the brine for several months. Olives stored in brine will keep for many years and do not need to be refrigerated. Green olives are treated to kill bacteria, but the temperature used is much lower, and the cooking time is less. That same pasteurization process is used to make milk safe for drinking. The temperature is sufficient to kill bacteria but not high enough to cook. Glass-stored olives are preferred by many people because you can see the olives inside.

There is another reason to store brine olives in jars. Brine in metal cans tends to corrode the can.

Green olives do not have oxygen added to them. The high salt content and high pH level (very acidic) inhibit bacteria growth. So green olives do not have to be put in a can and cooked. Besides, the high temperature used for cooking black olives would break glass jars.

The olive is native to the Mediterranean region and has been cultivated for 6,000 years. The olive is mentioned in Homer’s Odysseus and Iliad. The Bible has 30 references to the olive. It was an olive leaf that the dove brought back to Noah as an indication that the flood was over.

The olive branch is a symbol of peace and abundance. Olive oil has been prized as a grooming tool, used in lamps and for cooking food.

That’s about olive the information I have about olives.

Email questions and comments to:

Larry Scheckel is a retired Tomah High School physics teacher.


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