Lactic Acid Fermentation Explained

Johanna Tanhuanpää
Sep 10
3 min read

Updated: 5 days ago

Fermentation is a metabolic process in which cells extract energy from food without using oxygen (anaerobically), by breaking down sugars into simpler molecules and releasing a bit of energy in the process.

The two main types of fermentation are lactic acid fermentation and alcoholic (ethanol) fermentation. As the name suggests, lactic acid fermentation is done by lactic acid bacteria – and also our own (and other animals') muscle cells during intense exercise when oxygen is scarce. Yoghurt, sauerkraut, sourdough bread, kimchi and of course silage are examples of products made by lactic acid fermentation. Alcoholic fermentation, on the other hand, is done by yeast and also some bacteria. Beer, wine and yeast-baked bread are familiar examples of products made by alcoholic fermentation.

What to Take into Consideration for Lactic Acid Fermentation

In agriculture, lactic acid fermentation is a process familiar to many from silage production. Key things to know about the process can be summarised in three bullet points:

It needs sugars: from grass, grains, molasses or even table sugar.
It happens when air is limited: packed silage, slurry pits, inside the animal gut, airtight containers.
Lactic acid is produced, which lowers pH and slows down spoilage bacteria.

Below are some practical considerations when doing lactic acid fermentation.

Raw material: sugars & cleanliness

a) Quality of material

Use fresh and healthy raw materials – no visible rot or mold.
When fermenting plant materials, note that younger forage → more sugars → faster lactic fermentation.

b) Hygiene

Wash or shake off excess soil where realistic.
Remove obviously rotten or moldy parts.
Dirty input = more unwanted bacteria, clostridia, and molds competing with lactic acid bacteria.

Containers & equipment

a) Container type

Must be non-reactive, clean and easy to seal:
- Silage: bunkers, clamps, bags, towers, bale wrap.
- Small ferments: food-grade buckets, glass jars, plastic barrels with tight lids.
Avoid rusty metal that can corrode; food-grade plastic or glass is ideal.

b) Cleanliness

Clean equipment (choppers, wagons, buckets, knives, jars) to reduce “wrong” microbes.
You don’t need sterile, but you do want “clean enough you’d eat from it.”

c) Excluding air

Pack nad press material very tightly to push out air.
Fill the container as full as possible, leaving little headspace.
Use weights on top.
Good sealing (plastic sheets, lids, gaskets) is crucial → less oxygen, less mold.

Salt and/or starter culture (if applicable)

Salt (for vegetables):
- Helps select for lactic acid bacteria and keeps spoilage microbes down.
- Too little → soft, unsafe ferments; too much → fermentation slows or stops.
Starter cultures / inoculants:
- Silage inoculants or lactic acid bacteria starters can:
  - Speed up pH drop
  - Improve consistency
  - Reduce spoilage
- Follow manufacturer’s dose instructions – overdosing rarely helps and underdosing weakens the effect.

Temperature

Lactic acid bacteria are happiest at moderate, warm temperatures, but you don’t need to be exact.

Typical “good range”: roughly 18–35 °C
Too cold:
- Fermentation is slow.
- pH takes longer to drop, giving spoilage microbes a head start.
Too hot:
- Can kill or stress lactic acid bacteria.
- Can encourage other unwanted microbes.

On farm:

For silage, you don’t control temperature perfectly, but:
- Avoid ensiling very cold or frozen material.
- Avoid leaving chopped forage in a hot pile with lots of air before sealing (heating + spoilage).

For small barrel/jar ferments:

Room temperature (around 20–25 °C) is usually fine.

pH and acidity

The goal of lactic fermentation is to drop the pH fast and keep it low.

Target end pH depends on material, but roughly:
- Many vegetable ferments: final pH below 4.0
- Good grass/maize silage: often around 3.8–4.5
Low pH:
- Preserves nutrients
- Inhibits molds, clostridia, and spoilage bacteria

If you have a simple pH meter or pH strips, you can:

Check pH after some days(s) to see if it’s dropping.
Confirm the final ferment is in a safe, stable range.

Slow or weak pH drop usually means:

Not enough sugars, or
Too much air, or
Too few lactic acid bacteria / too many “bad” microbes.

Oxygen – your main enemy

Lactic acid fermentation is anaerobic – it needs low or no oxygen.

Key points:

Pack tightly to remove trapped air.
Seal quickly – don’t leave chopped material lying in a loose heap.
Check covers and lids for holes, tears, loose edges.
On silage faces: keep the feedout smooth and tight, don’t let air dig deep into the stack.