Fermentation of green grass clippings

Fermentation of green grass clippings typically refers to the anaerobic process of converting fresh grass into silage—a preserved fodder for livestock, or harnessing its sugars for biochemical production.

How fermentation works:

• When grass clippings are tightly packed and sealed from oxygen (in silos, barrels, or plastic bags), naturally occurring microorganisms, mainly lactic acid bacteria (such as Lactobacillus plantarum), ferment the plant sugars into organic acids—primarily lactic acid, but also acetic and sometimes butyric acid. This acidification preserves the grass and prevents spoilage^[1][2].
• The process usually requires reducing the moisture content to about 65% by wilting the grass, then packing it tightly to eliminate air spaces, sometimes adding fermentable carbohydrates like molasses to improve quality, especially when starting with grass lacking sufficient sugars^[2].
• Fermentation starts after about 48 hours and is mostly complete in two weeks, although storage for several months is common for optimal preservation^[1][2].

Practical methods:

• For small-scale or backyard use:
• Chop grass clippings into short lengths.
• Let them wilt to lower moisture.
• Mix (optionally) with diluted molasses for extra fermentable sugars.
• Pack tightly into an airtight container or barrel, using weights to compress.
• Seal and store in a cool place for at least a month; the top layer, which may mold, should be removed before use^[2].
• On a larger scale, the process looks similar to industrial silage production. The grass can also be "juiced" and fermented for the production of value-added chemicals. For instance, grass clip juice can serve as a substrate for microbial fermentation to produce chemicals like α-humulene using engineered bacteria such as Cupriavidus necator^[3].

Products and uses:

• Silage: Sour, acidic-smelling, and well-preserved; mainly animal feed^[1][2].
• Industrial biochemicals: After hydrolysis (breaking down cellulose into sugars, sometimes with acid treatment), grass can be fermented to create products like ethanol, xylitol, or α-humulene, though yields depend on processing methods and equipment^[3][4].

Risks and by-products:

• Grass clippings fermenting in a pile can build up considerable heat, sometimes enough to cause "smoking" or even spontaneous combustion if not managed well, especially in large, dense piles^[5].
• In open or poorly sealed conditions, spoilage microorganisms may produce unpleasant odors and reduce the quality of the preserved material^[1].

Summary Table: Key Aspects of Grass Clipping Fermentation

Stage	Key Actions	Microorganisms Used	Main Products	Common Uses
Silage (Animal Feed)	Wilting, Packing, Sealing	Native lactic acid bacteria	Lactic, acetic, butyric acid	Livestock fodder
Industrial Fermentation	Juice extraction, Hydrolysis, Fermentation	Engineered or wild-type strains (e.g. C. necator, yeast)	Chemicals, Alcohols, PHAs	Biofuels, biochemicals

Silage pile covered with plastic sheeting and tires at Feldpausch Farms.

Silage pile covered with plastic sheeting and tires at Feldpausch Farms.

In conclusion, fermenting green grass clippings is a well-established way to preserve nutrients and create animal feed or raw material for biotechnological applications. The process hinges on tightly sealing the clippings from oxygen, encouraging the growth of lactic acid bacteria, and sometimes supplementing with extra sugars for higher quality results^[3][1][2].

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• https://en.wikipedia.org/wiki/Silage     
• https://www.grit.com/farm-and-garden/making-silage-from-lawn-clippings-ze0z1410zdeh/      
• https://pmc.ncbi.nlm.nih.gov/articles/PMC9788380/   
• https://www.youtube.com/watch?v=yCGYY4xUMC4 
• https://www.reddit.com/r/composting/comments/12jmjzl/can_a_compost_made_of_mostly_grass_clippings/