A Taste of Plant Acid: Does High pH Make Vegetables Taste Acrid?

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Updated on Aug 29, 2011

The purpose is to determine if pH could be a factor in giving an onion an acrid taste.

Some vegetables have a strong, sharp, "acrid" taste, sometimes even stinging your tongue and nose. A good example is an onion. Yet, even among the onion family, there are differences in the strongness of their taste. Does the pH (the measure of alkalinity or acidity) differ in different types of onions (American onion, Spanish onion, and so forth)? If one type of onion has stronger taste than another, do you think the pH of the stronger onion is more acidic?

One characteristic of chemical substances is the amount of acid or base they contain. Foods that contain weak acids taste sour, for example, lemon or lime juice, and pickles. Strong acids may be hazardous, as they can damage your skin and other parts of your body. The opposite of an acid is a base, also called an alkali. Bases have a slippery feel to the touch. They taste bitter. Examples of substances that are bases include ammonia and other cleaning products, milk of magnesia, baking soda, and soap. Products that unclog household drains contain strong bases, and they can be hazardous to touch.

In the same way as a ruler is used to measure the length of an object, and a thermometer is used to show how hot something is, chemists have created a scale to measure how much acid or base a substance contains. This measurement tool is called the pH scale. Technically, the term "pH" means "the potential of electricity for positive hydrogen ions," because chemists can use electricity to do the measurement.

The pH scale goes from 0 to 14, 0 as the strongest acid, 7 s neutral (in the middle), and 14 as the strongest base. Pure water has a pH of 7. If you have a swimming pool, you may have used a pH water-test kit, where a sample of water is collected, and a few drops of a special chemical are added and mixed with the water. The resulting color of the water is matched against a color comparator chart to find the exact pH.

One way to measure pH is by using litmus paper. Litmus paper comes in different colors to measure different ranges of pH. Red litmus paper turns blue in a base solution. Blue litmus paper turns red in an acid solution. A color chart is used to compare the color litmus paper turns to a pH number.

Hypothesize that among several types of onions, the ones with the stronger (more acrid) taste have lower pH values (will be more acidic) than the others.

  • As many different types of onions as you can find
  • pH test kit with color comparator

Gather as many different types of onions as you can. Squeeze juice from each type and use a pH test kit to determine the pH of the juice. Taste a small amount of the juice of every onion, and then compare the strongness of each. Compare the tastes to the pH of each onion. Do the onions with a stronger taste have a lower pH?

Note: If the pH is more acidic in stronger-tasting onions, this poses an interesting correlation. However, it does not prove that pH is the only factor involved in making the onions taste more acrid. Additional research would have to be done.

Write down the results of your experiment. Document all observations and data collected.

Come to a conclusion as to whether or not your hypothesis was correct.

Something More

Compare the pH of various other vegetables. Is there an association with sharp taste to pH? Does a red bell pepper have a different pH than a green bell pepper? Compare the pH of various citrus fruits to their taste.