Yeast

Yeast may help bread rise, beer froth, and wine ferment, but what does it do in the garden?

Is yeast a plant? An animal? Actually, yeast is a one-celled, sugar-eating fungus that urinates alcohol and farts carbon dioxide. It is those farts that make bread rise, and the other excretion that puts alcohol into beer and wine. 

Beer and bread produced with yeast (Jon Sullivan) Public Domain

Yeasts have been around for hundreds of millions of years. In many ways, yeasts and other fungi are a lot like plants, but they are different in many ways, too.

Yeast vs. plant cells

Yeast cells are smaller than plant cells. While plant cells can become leaf, stem, fruit, or root cells, yeast cells remain the same one-celled creature. Like plant cells, yeast cells have a cell wall, but it is not made out of cellulose. Both yeast and plant cells have membranes, but they are made out of different materials. Yeast cells do not have chlorophyll-producing chloroplasts, either, which is why they do not use sunlight to make food. Inside a plant cell, you can find food stored as a starch, whereas yeasts store food as sugar. 

Other common fungi include mushrooms and molds. The yeast you buy in the store to make bread, beer, or wine is called Saccharomyces cerevisiae.

How do yeasts grow?

Yeasts do not require sunlight to grow. Yeasts feed on dead, decaying matter, making them saprophytes. They are also parasites, which makes them heterotrophs. Instead of using the sun’s energy to generate food, fungi absorb carbon, in the form of sugars, organic acids, and other easy-to-digest carbon-based edibles from their hosts. This is why you will often see fungi growing on the skins of apples, grapes, or peaches. Yeasts grow best when the environment has a neutral or slightly acidic pH. ​

Mitosis (Public Domain)

Yeast reproducing by budding (Public Domain)

Yeasts reproduce in a variety of ways, depending on the species and environmental conditions. The most common method of yeast reproduction is an asexual, vegetative method called budding. In budding, a clone offspring is produced as an attachment to the parent cell. When the clone, also known as a bleb or daughter cell, reaches maturity, it separates from the parent cell, leaving behind scar tissue. In some cases, these buds can link themselves together into chains, called false hyphae. Other yeasts reproduce using mitosis. In mitosis, the genetic information is duplicated and the nucleus of the cell is split in half, with each half being a twin to the other. Fission and meiosis are also used by some yeast species, but we digress

​Harmful yeasts in the garden

Yeasts love to eat sugar. As such, they can spoil fruits and vegetables before you ever get a chance to enjoy them. Yeasts can grow on almonds, pineapples, lettuces, and pretty much anything else you decide to grow. Peach leaf curl is also caused by a yeast. That being said, yeasts actually perform many beneficial services to your garden.

Peach leaf curl on nectarine

Beneficial yeasts in the garden

Yeasts are not all bad. When it comes to protecting your strawberries, cherries, and cane fruits from the invasive spotted wing drosophila, torula yeast is used to lure this pest to its death. Also, recent research has demonstrated that adding brewers yeast to the garden may help plants counteract the effects of toxins in the soil. In another amazing study, it was found that a yeast found on the bodies of pollinating bees gets knocked onto flowers, as bees move around. Those yeasts then feed on the sugars in the flowers’ nectar. Breaking down those sugars generates heat, which keeps the flowers and the surrounding air space (used by the bees) warmer. This helps both parties survive winter. Yeasts also play a role in soil aggregate formation, improving soil structure. While other yeasts are believed to be part of the sulfur and nitrogen cycles, and make insoluble phosphates available to plants. Yeasts are food for many bacteria, insects, and other soil predators.

If nothing else, adding yeast to the compost pile will speed decomposition, assuming moisture and temperature levels are appropriate.

Did you know that some yeast species produce toxins that kill off other yeast species?

Now you know.