FR2574633A1 - Method for extracting manioc (cassava) pulp, by dry means, particularly for preparing manioc (cassava) flour - Google Patents

Abstract

Method for extracting manioc (cassava) pulp by dry means. The method comprises the following successive stages: - mechanical peeling of the manioc (cassava) roots; - coarse grinding of the roots; - partial dehydration of the ground mixture; - drying; - fine grinding, and - screening. Manufacture of manioc (cassava) flour.

Description

 The invention relates to a treatment of cassava roots with a view to extracting the pulp therefrom.

 The pulp of a. cassava root is protected-by two. bark: the suber or outer bark and the inner bark called. often phelloderm. It further comprises in its center, a fibrous cord. During cassava processing it is necessary to partially or totally eliminate both. bark and the central cord to keep only the starch-rich part of the central cylinder. The suber or outer skin which represents 1 to 3% of the total weight of the root is sliced more or less according to the varieties. it is separable from the rest by scratching. The inner bark separates from the central cylinder at the level of the cambium by tearing. It represents 8 to 18% of the total weight of the root. In a mature root, this inner layer is usually 2 to 5 mm thick.

 Manual peeling of cassava is relatively easy but requires abundant labor because this work must be done as quickly as possible because of rapid physicochemical alterations after harvest. Beyond 24 hours, cassava peels badly. Manual peeling is only acceptable for low-capacity craft production. This is why for larger capacities, we tried to mechanize the peeling. Several peeling processes have been proposed which have never been satisfactory, either because the work was poorly done, and especially because the losses at the extraction were very high and led to excessive cost prices.

In addition, the requirements for peeling and grinding differ according to the intended purpose
- if it is to extract the starch, only the elimination of suber (first bark) is indicated.

The elimination of the central fiber is useless and that of the phelloderm is questionable because in the starchy houses of a certain importance, it becomes profitable to recover the starch which it contains,
- if it is a question of producing breadmaking flour, the preliminary removal of the first bark is essential because of the need to eliminate any risk of black spots.

for certain gari where the presence of fibers is sought, only the prior elimination of the two barks is necessary. That of the fibrous cord and fibers is not,
- if it is to produce a gari first choice and attiéké, the prior elimination of both bark? and fibrous cord is indispensable.

 it therefore appears that when we speak of "peeling", we must clearly specify what we seek to eliminate -if we say that it does not make any sense in particular about the returns, losses and capabilities.

That's why it's better to talk
- dehulling for the first bark,
- peeling for the second bark,
- Defibering for the fibrous cord.

 The extraction of the pulp results from the three preceding operations.

The purpose of the present invention is to
to provide a process for producing industrially
extraction of the pulp, in particular with a view to
bread-making manioc flour, so that the product
obtained does not contain more than 15% by weight of the total phelloderm of the raw material.

This is achieved according to the invention in
submitting the cassava root, that is to say
not dehydrated, to the following operations
- mechanic scrubbing with manual supplementation
- coarse grinding of the dehulled root
abut to grind the pulp without grinding the phelloderm
nor the fibrous cord
- partial dehydration, by pressing and / or centrifugation, of the mixture obtained
drying of the dehydrated product
- grinding the dried product and sieving to separate the unwanted parts (phelloderm and fibrous cord fragments)
- optionally recycled successive sieve to a grinding and sieving increasingly fine.

 The process is suitable for preparing bread-making manioc flour and fermented cassava flour.

The following diagram shows the different steps of the process which is the subject of the present invention
DIAGRAM

<tb><SEP> ROOTS <SEP> FROM <SEP> MANIOC <SEP> FRESH
<tb><SEP> Mechanical Dewaxing <SEP>
<tb><SEP> I
<tb> Inspection, <SEP> trimming, <SEP> tailing
<tb><SEP> Wash
<tb><SEP> Crushing <SEP> Rude
<tb><SEP> (Fermentation)
<tb><SEP> Partial <SEP> dehydration
<tb><SEP> Drying
<tb><SEP> I
<tb><SEP> Crushing <SEP> end
<tb><SEP> i <SEP> t <SEP> n <SEP> times
<tb><SEP> I <SEP> Sieving <SEP> l
<tb><SEP> J
<tb><SEP> I
<tb><SEP> FLOUR <SEP> iDE <SEP> CASSETTE
<Tb>
Dehulling is preferably done
by rubbing the roots against each other and
against the walls in a rotating drum, preferably
under a sprinkling of water that washes the roots and ensures
the removal of suber particles.
depend on many parameters
- the state of cassava freshness: on a
fresh cassava, the film comes off easily by
friction, while on a cassava of more than 24 hours,
it adheres more strongly.

- the variety of cassava: some varieties of cassava are easier to remove than others;
- the age of cassava: we note that the aging of the roots increases the strength and the adhesion of the first bark;
- the shape of cassava: some varieties are less polymorphic than others and their more regular forms - the absence of concavities and deformation - (grooves - protuberances, etc.) facilitates skinning;
- The presence of shocks: it is necessary to burst the first bark by shocks in order to-take off and form pendent flaps from which a final tearing by friction and water jets will be possible;
- presence of vigorous but non-abrasive rubbing
- presence of jets of water whose kinetic energy is sufficient to detach and cause the flakes of first bark;
- the rotational speed of the drum, which determines the number and intensity of shocks and the vigor of the friction
- the loading rate which determines the vigor of the friction and the intensity of the shocks
- the residence time in the drum which conditions the degree of skinning
- the absence of iron in contact to prevent the formation of blue ferrocyanide.

 Experience shows that due to the polymorphism of cassava, it is useless to want to de-lime 100%. This is why, after dehulling, the roots are inspected, possibly trimmed, hulled, then washed.

 They are then conveyed to a mill which is preferably of the type comprising a rotatable fluted cylinder cooperating with a fixed counter-plate to determine between them a degressive passage interval for the roots.

However, one can use a different type of mill, for example a hammer mill. The characteristics of the mill are chosen such that the roughly ground pieces of pulp have a thickness of about 2 mm. The length of the various elements of the ground mixture - pulp, phelloderm and fibers - is very variable.

 The mixture leaving the mill is optionally subjected to fermentation depending on the final product that is desired: breadmaking cassava flour for which there is no fermentation or fermented cassava flour (called "fou-fou") for which there is fermentation.

 The mixture - fermented or not - then undergoes partial dehydration by pressing and / or centrifugation. Then the dehydrated mixture is dried. This operation is performed in a manner known per se, for example on a heating mat, at a relatively high temperature of up to 950C. The weight of moisture content of the dried product is of the order of 10%.

 After drying, the product is ground in a fine grinder, with hammers or grinding wheels, which takes advantage of the difference in grinding resistance of the pulp, the phelloderm and the fibrous bead. The pulp exhibits isotropy in crush strength. In other words, its fragility is the same in all directions. On the other hand, the phelloderm has a layer structure reinforced by cellulose which gives it a greater resistance perpendicular to this structure. This anisotropy makes it possible to separate the shreds of phelloderm from the friable pulp under shock.

The same thing occurs for the fibrous bead which has a preferred direction of resistance due to the presence of cellulosic fibers in longitudinal bundles which give it a great deal. hash dry strength. This results in pieces of fiber much larger than the friable pulp, which bursts under the shocks.

Following sieving, the larger particles will generally be phelloderm or fibrous particles and will be retained in the rejection. The sieving of the ground product is carried out by sieves with a mesh diameter of about 200 microns. If we want to improve the extraction, we can recycle one or more times the refusal in another sieving crushing cycle to extract by differential grinding the last parts of pulp still adhering to the fiber and phelloderm.

 However, the rate of extraction is limited by the rate of entrainment in the flour of waste rich in cellulose and ash.

Claims (1)

 SINGLE CLAIM  A process for extracting dry cassava pulp in which the freshwater cassava root is subjected to the following operations  - mechanical depelliculation,  - coarse grinding of the queen in question,  partial dehydration of the mixture obtained by grinding,  drying of the dehydrated product,  - fine grinding of the dried product,  sieving of the crushed product to separate the phelloderm and the fibrous cord,  - possibly successive recycling of the sieved pulp to a grinding and sieving increasingly fine.