What is the step-by-step process of microbial lacto-fermentation?

Reuben Sandwich Photo One of the many in-depth science-based books we’ve collected and read through the years, The “Handbook of Fermented Functional Foods”, p. 349, illustrates the step-by-step progression of lactic-acid bacteria and yeasts, using sauerkraut as an example:

  • Is a spontaneous, complex microbiological process
  • Has a strict sequence of different microorganisms – “this” must occur before “that”
  • Crucial to understand is that this type of a process shifts from aerobic to anaerobic – a very critical step for the overall-health and stability of the final brine and fermented food.

The same process applies to ALL fermented foods, whether dairy, grain, vegetable or fruit. The goal is the creation of lactic acid by the lactic acid bacteria.

Amazingly, anaerobic lactobacillus bacteria (LAB), the “good guys”, which are crucial and foundational to lacto-fermentation”, are only available in EXTREMELY small numbers – only about 0.15 to 1.5% of the total bacterial population, primarily belonging to Leuconostoc mesenteroides ssp. mesenteroides at the beginning of the process.

The other bacteria are aerobic – pseudomonads, enterobacteriaceae, and coryneforms – and dominant in the beginning, but….

The Science Graphic The Pickl-It fermentation system creates and maintains a healthy environment (inside the fermenting vessel) that supports the “good guys” – the anaerobic lactic acid bacteria, reducing the undesirable aerobic bacteria.

Four distinct successive stages of lacto-fermentation:

Graphic No 1

Fermentation begins the moment the cabbage is filled into containers. Must be tightly packed so that aerobic bacteria (Pseudomonas, Flavobacterium, and Acinetobacter species – the microbes you do *not want to have in your ferments) are deprived of oxygen, and are immediately diminished.*

  • Anaerobic bacteria use up oxygen, causing them to multiply over next 2-3 days
  • pH immediately changes
  • Lactic, acetic, formic and succinic acids form

Graphic No 2

Shift in fermenting environment to anaerobic, with the salt and reduced pH working together, supporting the anaerobic lactic-acid bacteria (LAB), Leuconostoc mesenteroides which:

  • Initiates fermentation
  • Is well-adapted to substrate
  • Present in substantial numbers
  • Produces lactic and acetic acids (4:1), further lowering pH
  • Because Lc. mesenteroides is heterofermentative LAB, produces the all-important carbon dioxide
  • Further reduction in oxygen and anaerobic atmosphere provides stability for Vitamin C (ascorbic and dehydroascorbic acid)
  • Color of food is stabilized
  • Other heterofermentative LAB begin growth: Lc. fallax, followed by Lb brevis (more acid and salt-tolerant than Leuconostocs)
  • Depending on temperature, these first two stages are completed in 3 to 6 days. Lactic acid will have increased to approximately 1%.

Graphic No 3



Lactic acid bacteria shift to homofermentative LAB which dominate due to anaerobiosis, lowered pH and elevated levels of salt.

  • Dominating homofermentative LAB are subgenus Streptobacterium
  • Lb plantarum only comprises 30 to 80% with Lb. sakei (plays key role in fermented dairy) and Lb. curvaitus present in large numbers in sauerkraut
  • Remaining carbohydrates (glucose, fructose and sucrose) to organic acids, primarily lactic acid
  • Lactic acid increases to 1.5 to 2.0%; Lactic:Acetic acid ratio – 4:1
  • pH of 3.8 to 4.1, at this stage, produces a mild-flavored sauerkraut
  • Food processors in Europe typically unpack and pasteurize at this point

Graphic No 4



Only fresh, unpasteurized sauerkraut will undergo the final stage for full nutritional and flavor development.

  • Lb. brevis and some other heterofermentative species metabolize pentoses – remaining sugars – such as aribinos and xylose which become dominant (living plant material normally does not contain free-pentoses)
  • Pentose are further fermented to lactic acid
  • The resulting flavor of sauerkraut is a combination of: lactate, acetate, ethanol, carbon dioxide and diacetyl.
  • Total acid increases to 2.5%
  • pH decreases to as low as 3.4


Tiny Dill 500 Bar

Sources:

Food Chemistry, 3rd edition , edited by Owen R. Fennema, Marcel Dekker, Inc., New York, NY ISBN 0-8247-9691-8 provides a schematic diagram of the formation of volatile fermentation products.

Genera of Lactic Acid Bacteria By Brian J. B. Wood, W. H. Holzapfel. (Preview)

Handbook of Fermented Functional Foods, Functional Foods and Nutraceuticals Series, Edited by Edward R. Farnworth, PhD, CRC Press; ISBN 0-8493-1372-4