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Roots and tubers from Republic of the Congo

Dry sack retting of cassava (rouissage à sec)rouissage à sec

Dry sack retting is a way to ret cassava roots without soaking them in water, worked out in Congo in the early 1990s. Cut roots are packed tightly into a gas-tight sack, which was chosen to copy the semi-anaerobic conditions of water retting, and they ret in 3 to 4 days. A 24-hour soak afterwards removes the strong taste, giving flour as good as from water retting.

Fully documentedRoots and tubers4 days – 5 days

Recipe

No fixed amounts recordedThe report describes the method, not batch sizes.
Cassava roots, cut into slices or cubes (slices about 3 cm)[orstom1992]
Water for a 24-hour post-soakThe soak water can be reused, so little water is needed[orstom1992]

Total time across the recorded steps: 4 days – 5 days

Start
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What changes: Cassava roots are cut into slices of about 3 cm

Step 1 of 4
Cut the roots into slices or cubes
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented
Which microbes the steps name, step by step
Lactic acid bacteria

Whole roots retted in a sack took up to 30 days, retted unevenly and built up lactate and butyrate that gave a strong taste. Cutting into slices or cubes cut the time to 3 to 4 days, slices of about 3 cm made the retting as even as traditional retting, and a 24-hour soak afterwards fixed the taste [orstom1992]. Output: cut roots.

Flavour
Not documented
Texture
Not documented
Colour
Not documented

Microbes at work in this step

Not documented for this step.

Method

Measured measured in a studySet fixed by a specification or tested recipeReported one source reports itTypical a general value, not sourced for this fermentUnconfirmed not yet checked against a source

At a glance

Dry sack retting is a way to ret cassava roots without soaking them in water, worked out in Congo in the early 1990s. Cut roots are packed tightly into a gas-tight sack, which was chosen to copy the semi-anaerobic conditions of water retting, and they ret in 3 to 4 days. A 24-hour soak afterwards removes the strong taste, giving flour as good as from water retting. Made in 4 steps over 4 days – 5 days. The longest step, pack tightly in a gas-tight sack and let them ret, takes 3–4 days (Trèche S 1992). In water retting, a related method, Leuconostoc mesenteroides (heterofermentative), dominant in the active phase and In water retting, amylolytic Lactobacillus plantarum, taking over at the end do most of the fermenting.

Key numbers
Main step3–4 daysReported[orstom1992]Pack tightly in a gas-tight sack and let them ret

What makes this one different

Ordinary retting soaks whole roots in a river, pond or drum for days. Here cut roots ret in a gas-tight sack with no water, and only a short soak follows [orstom1992]. Losses are lower in sack retting than in river retting [orstom1992].

Related ferments

Safety

Retting breaks down most of the cassava's cyanogenic compounds, mainly through the roots' own linamarase [brauman1996, orstom1992]. The retting medium had little effect on detoxification, which was faster in roots peeled first [orstom1992]. Soft roots are not proof the cyanide has gone. In the same report's retting trials, total cyanide after 3 days was 47 ppm in peeled roots and 150 ppm in unpeeled ones; it was under 6 ppm after 5 days and in the flours [orstom1992]. The sack is sealed and low in oxygen, and the report gives no pH for it. WHO says C. botulinum grows without oxygen and not below pH 4.6. It says boiling destroys the toxin, for example above 85 °C inside for 5 minutes or longer, but the spores can survive boiling. No study we read tested sack-retted roots for it, so bring whatever is made from them to that heat.

Hazards the sources name: Clostridium species, strict anaerobes that make butyrate and add to the strong flavour in water retting.

History and sources

Every number is labelled with how it is known. How this atlas is made

Developed in the Congo operation of the ORSTOM programme on improving cassava-based fermented foods; the final report of 1992 called the technique operational, with a pilot evaluation under way [orstom1992].

Starter
The sources we found do not say how its fermentation begins.
Temperature, salt and pH
The sources we found give no temperature, salt or pH figure for any of its steps.
  1. [orstom1992] Trèche S., Brauman A., Legros O. et al. 1992, Amélioration de la qualité des aliments fermentés à base de manioc, opération Congo (rapport final), ORSTOM, Paris, 66 p., section 2.4 "Mise au point d'une technique de rouissage à sec" and section 3.1.1 (read from a web.archive.org copy, the IRD server being down)archive
  2. [brauman1996] Brauman A., Keleke S., Malonga M., Miambi E., Ampe F. 1996, Microbiological and biochemical characterization of cassava retting, a traditional lactic acid fermentation for foo-foo (cassava flour) production, Appl Environ Microbiol 62(8):2854–2858, doi:10.1128/aem.62.8.2854-2858.1996 (abstract; water retting)paper
  3. [giraud1996] Giraud E., Brauman A., Kéléké S., Gosselin L., Raimbault M. 1996, A lactic acid bacterium with potential application in cassava fermentation, in Dufour D. et al. (eds), Cassava flour and starch, progress in research and development, CIRAD and CIAT, p. 210–220 (IRD record abstract)book
  4. [who-botulism] World Health Organization, Botulism, fact sheetgov