Gums

Your chewing gum is made from trees. Well, it used to be.

Unwrapped stick of chewing gum (Lusheeta)

Tree gums have been used as a chewable treat for over 9,000 years. Mayans and Aztecs used gum from the chicle tree. Ancients Greeks used gum from the mastic tree. Native Americans used gum from spruce trees. It was the Americans, however, who make chewing gum famous to the point that there were not enough trees to produce the gum needed to make gum. It is estimated that over 100,000 tons of chewing gum are consumed each year. Most modern chewing gum is made with natural and/or synthetic rubber and not botanical gums.

But gum isn’t the only goo produced by plants.

Plant oozes

Plants ooze several different substances. Gum is only one of them. Plants also produce fats and oils, latex, mucilage, resin, and waxes. The fats and oils produced by plants are more commonly known as essential oils. Essential oils can be responsible for a plant’s unique smell or flavor. Latex is the milky white emulsion of defensive chemicals seen oozing from broken dandelion stems. Mucilage is used to store food and water, thicken membranes, and in seed germination. Succulents and flax seeds have particularly high mucilage contents. Resin is a viscous mixture of antibacterial, antimicrobial acids commonly seen in conifers. Resin dries to a hard, crystalline structure. And then there is plain old sap. 

Sap has different components, depending upon where it is found. Xylem sap carries water, hormones, and minerals from the roots to the leaves. Phloem sap conducts sugars, hormones, and minerals from leaves, where carbohydrates are produced through photosynthesis. Sap generally stays fluid. Gums are a specialized type of sap produced by woody plants.

Natural gum of plum tree (Rencas) CC BY-SA 3.0

[Plum gum? Sorry, I couldn't resist.]

​How do plants use gums?

Gums are produced in a process called gummosis. Gumming refers to the way some plants can break down internal tissues, particularly cellulose, to create a high-sugar sap, or gum, used to seal off wounds and surround invading insects. Gums are commonly found in conifers, such as pine and spruce. Some plants, such as Western poison oak, use gums as protective, gummy seed coatings that delay germination.

How do we use botanical gums?

Botanical gums are water-soluble sugars that are commonly used in the food industry as emulsifiers, thickening agents, and stabilizers. They are also used as adhesives, in printing, candy-making, paper-making, and to make chewing gum. 

If you look at ingredient lists on packaged food (and I urge you to do so), you may see some of these botanical gums:

• guar gum - from guar beans
• gum arabic - Acacia tree sap
• gum ghatti - Anogeissus tree sap
• gum tragacanth - Astragalus tree sap
• karaya gum - Sterculia tree sap
• locust bean gum - from carob tree seeds

Gums are frequently collected by tapping or otherwise wounding trees with incisions or by peeling back sections of bark. The trees respond to these wounds by gumming. 

Tapping is the method used to collect the sap from sugar maple trees to make maple syrup. A tap consists of a metal tube with a downward-pointing lip and a notch or hook from which to hang a bucket. The tube end is hammered into a tree to reach the xylem and a bucket hung from the lip. Sap from the xylem flows (very, very slowly) through the tube, down the lip, and into the bucket. From there, the sap is cooked down to reduce the water content. More modern set-ups use plastic tubing. My students and I once made a delicious syrup/caramel from silver maple trees.

Some of these gums stay soft, while others harden into “tears” which are broken off for processing. If you see gums oozing from your trees, take a closer look.