Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Reexamination Certificate
2002-01-14
2003-05-27
Lilling, Herbert J. (Department: 1651)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
C426S011000
Reexamination Certificate
active
06569653
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes for producing ethanol from starchy plant raw material. The invention applies particularly to the production of ethanol as a fuel, but also to the chemical, pharmaceutical and cosmetics industries and, after rectification in order to remove aromatic substances, the food industry. The invention especially uses as starting material a wheat, corn, barley, sorghum, rye or rice must.
BACKGROUND OF THE INVENTION
A process for producing ethanol which consists in subjecting a starchy plant material must to an enzymatic liquefaction treatment in order to obtain a liquefied must is already known. The liquefied must is then subjected to an at least partial enzymatic saccharification treatment in order to obtain a saccharified must. The starch is at least partially converted into glucose. The saccharified must is then divided into a first portion and a second portion. The first portion of the saccharified must is diluted with a diluent and is placed in contact in a prefermenter with a yeast of the genus Saccharomyces in order to obtain a yeast suspension. The proportion of diluent, which is generally water and/or vinasse, is such that the alcoholic degree of the yeast suspension is less than 6% by volume, with the effect that an excessively high alcohol concentration does not prevent the yeasts from growing. This yeast suspension is then placed in contact with the second portion of the saccharified must in a fermenter for a time which is sufficient to obtain a wine with an ethanol content above a given threshold. In usual practice, this time is proportionately longer the higher the ethanol content. For example, when the saccharification time is 20 h, a contact time in the fermenter or fermentation time of 40 h must commonly be allowed for in order to obtain an ethanol content of greater than 9% with a sugar content of less than 1 g/l. It has already been recommended to reduce the time for the saccharification operation to 10 h by arranging it such that the saccharification takes place also during the fermentation time which is kept at 40 h. The total time for the operations is thus 50 h. In order to obtain ethanol, the wine is distilled. During this distillation, an extraction of the “unpleasant tastes”, which correspond especially to the esters, is carried out so as to be able to obtain ethanol containing less than 500 parts of esters per million, as is commonly required for the use of ethanol as a fuel. It is also necessary to add acid to the prefermenter continuously in order to maintain a certain level of bacterial asepsis and to disinfect the circuits with disinfectant.
SUMMARY OF THE INVENTION
The invention overcomes these drawbacks by means of a process for producing ethanol which is much shorter than the prior-art processes, which directly gives by distillation an alcohol with such a small ester content that it is no longer necessary to allow for extraction of this ester content, thereby making it possible to dispense with any addition of acid to the prefermenter and to reduce the amount of disinfectant used in the manufacturing circuits, while at the same time having, all conditions being otherwise equal, wine with a higher alcoholic degree and the same low sugar content.
The subject of the invention is a process for producing ethanol which consists in placing a starchy plant raw material must in contact with a liquefaction enzyme in order to obtain a liquefied must, placing the liquefied must in contact with a saccharification enzyme in order to obtain an at least partially saccharified must, preparing in a prefermenter a suspension of yeasts of the genus Saccharomyces in a nutrient medium, placing the saccharified must in contact with an amount of the yeast suspension which is sufficient and for a time which is sufficient to convert the sugars contained in the saccharified must into ethanol, giving a wine with a sugar content of less than 3 g/l, preferably less than 2 g/l and better still less than 1 g/l for a wine alcoholic degree of at least 9.5% on a volume-for-volume basis, and distilling the wine in order to obtain ethanol, characterized in that it consists in removing substantially all the yeasts present in the prefermenter and in replacing them therein with fresh yeasts at a time interval such that the concentration of microorganisms, other than the yeast of the genus Saccharomyces, in the prefermenter remains less than a given threshold during the interval following the replacement of the yeasts.
Specifically, it has been found, unexpectedly, that the very long contact time of the yeast suspension with the saccharified must, which was necessary hitherto, is due to the fact that in a relatively short space of time the yeast of the genus Saccharomyces suffers degeneration, mutation and/or contamination with another microorganism, especially with a yeast of the genus Brettanomyces which is much less active. By replacing all the yeasts with fresh yeasts of the genus Saccharomyces before this phenomenon takes place, and in particular preferably before there are 10
7
cells per milliliter, and better still 10
5
cells per milliliter, of a microorganism other than the yeast of the genus Saccharomyces in the prefermenter, the activity of the fermentation yeasts is maintained, thereby making it possible to reduce the contact time in the fermenter, to have virtually no more ester during the distillation, to have a higher alcoholic degree, to dispense with the need to add acid to the prefermenter and to reduce the amount of disinfectant. The freshness of the yeast suspension is of fundamental importance regarding the duration of the step for converting the sugars into ethanol. Supplying fresh yeasts to yeasts that are already contaminated gives only a very transient improvement in the contact time required. In order to keep the continuously shortened contact time desired, it is necessary to remove virtually all the old yeasts before adding fresh yeasts.
DETAILED DESCRIPTION OF THE INVENTION
The presence of Brettanomyces in the prefermenter may be detected by taking a sample of the yeast suspension and examining it by microscope. Whereas Saccharomyces, and especially
Saccharomyces cerevisiae
, have an ovoid shape, Brettanomyces have an elongate shape. It is also possible to know by experience the interval to observe for the addition of the fresh yeasts and to systematically replace the spent yeasts with Saccharomyces yeasts at a time interval of less than 4 days.
According to one preferred embodiment, the process consists in diluting a first portion of 10 to 30% and preferably of 15 to 20% of the weight of the saccharified must in order to obtain a weak must, the rest of the saccharified must constituting a strong must, in prefermenting the weak must in the prefermenter in order to obtain a prefermented must and in placing the strong must in the presence of the prefermented must in a fermenter for a time which is sufficient to obtain wine.
Preferably, fresh yeasts are supplied to the prefermenter in an amount such that a concentration at least equal to 106 cells per milliliter approximately and preferably 10
7
cells per milliliter is obtained in the prefermenter.
It has been found, especially for a threshold of 9.5% for the wine ethanol content, that the sum of the saccharification time and the contact-time in a fermenter is only 35 h.
The first stage of the process according to the invention consists in subjecting a starchy plant material must to an enzymatic liquefaction treatment in order to obtain a liquefied must.
The plant material, in particular wheat, is ground, for example by one or two treatments in a hammer mill (of the brand PROMILL Promill-Stolz, RN 12 Serville, 28410 BU, 3000 rpm, or of the brand JACKERING Vorsterhauser Weg 46 PO BOX 1733 , 59007 HAMM) rather in the cases where the bran particles are not separated from the flour, and in one or more roll mills (in which the milling is more homogeneous) rather in the cases where the bran particles are separated from the flour, or any other type of mill.
Alard Georges Maurice
Brasseur Luc Robert
Gérard Mourin Alain Yves
Roux Philippe Jean
Bio-Ethanol Nord Picardie
Lilling Herbert J.
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