Food or edible material: processes – compositions – and products – Inhibiting chemical or physical change of food by contact... – Treating liquid material
Reexamination Certificate
1997-09-15
2004-02-17
Sherrer, Curtis E. (Department: 1761)
Food or edible material: processes, compositions, and products
Inhibiting chemical or physical change of food by contact...
Treating liquid material
C426S330300, C426S590000, C426S592000, C426S495000
Reexamination Certificate
active
06692786
ABSTRACT:
BACKGROUND
The intention is that due to the filtration of beer yeast and other sources of turbidity as well as colloidally dissolved substances, in particular albumens are to be removed in order to afford to the beer a clear non-glossy appearance and to increase the chemical physical as well as biological shelf life.
Apart from kieselgur filtration, until now used most frequently, attempts are being made to employ other filtration processes particularly having regard to the cost-intensive disposal of the kieselgur sludges. Such a process is the cross flow microfiltration in which the unclarified or preclarified beer in a filter unit flows over a porous membrane whereby between the crossflow or non-filtrate side and the opposite filtrate side of the membrane a-transmembrane pressure is set up whereby part of the beer flowing over the membrane penetrates the latter in transverse direction and is collected on the filtrate side as a purified filtrate. During this filtration the components to be filtered off precipitate on the membrane surface on the non-filtrate side, partly as a coating. To ensure the penetration of the membrane during the entire filtration process, this coating must not become too compact.
From EP 0 351 363 A1 the cross flow microfiltration of beer is known wherein the beer simultaneously during the filtration is stabilised by means of a stabilising agent, preferably PVPP. In order to avoid premature clogging of the membrane pores, a granular or fibrous filtration aid is additionally admixed to the beer to be filtered and settles on the membrane for the purpose of preventing clogging of the membrane pores due to the turbidity sources, etc. Kieselgur or perlite may, for example, be used as such filtration aid.
Although it is possible in this manner to prevent the particulate components of the beer from clogging the membrane pores, it is not possible by means of this process to intercept the colloidal substances, in particular albumens by means of the filtration aid. These colloidally dissolved components at the low temperatures required for the beer filtration of about 0° C. form a gel or jelly-like mass which permeates the covering layer and unavoidably clogs the membrane pores. As a result the effectiveness of the filtration is relatively rapidly reduced. For that reason provision is made, according to the aforesaid European patent application, to clean the membrane after concluding the filtration process. This may be attained by rinsing, increasing or reversing the crossflow velocity or by backwashing, in that a certain amount of filtrate is forced from the filtrate side through the membrane onto the non-filtrate side. The periodic membrane cleaning proceeds more particularly by rinsing, whereby the covering layer is initially partially coarsely removed, and by means of subsequent rinsing with hot caustic liquor and a sterilisation is cleaned and regenerated simultaneously with the PVPP being used in the plant as a stabiliser. However, the cost of this cleaning is relatively high and time-consuming and reduces the effectiveness of the filtration.
From EP 0 427 376 A2 a Cross flow microfiltration plant is known in which the feed pump is installed in a diagonal branch of a ducting loop comprising four branches, a closure valve being provided in each of the branches of the loop. At the branch points to which the pump is connected, the inlet from a feed tank or the return duct to the feed tank is connected whereas the two remaining branch points are connected to the two ends of the filter module. By opening and closing of appropriate valves it is possible with this filtration plant to reverse the crossflow direction of the liquid over the membrane. In addition, it is possible by appropriate settings of the valves to draw liquid from the filtrate side through the membrane in order to thereby more or less break down the coating. However, this succeeds only partially since during the filtration of beer the membrane pores also become clogged by the gel or jelly-like colloidally dissolved substances which in contrast to other particles of the covering layer cannot be removed readily by backwashing; rather, the liquor drawn through the membrane will select the way of least resistance, that is to say will flow through the membrane only wherever the membrane is locally pervious. Complete cleaning of the membrane is not possible by such a process.
A so-called integrated backwashing of the membrane is also known wherein the transmembrane pressure across the membrane is adjusted, for example by throttling the filtrate discharge, in such a manner that part of the membrane, e.g. that half which in the direction of flow is rearmost is permeated by the filtrate from the filtrate to the non-filtrate side, resulting likewise in a portion of the covering layer present there to be removed; cf. S Ripperger,
Mikrofiltration mit Membranen
, Verlag Chemie, Weinheim, 1992, page 133.
It has furthermore been proposed to employ a plurality of measures for the control of the covering layer, for example the just mentioned integrated backwashing and in addition thereto during a brief interruption of the filtration, the backwashing and regeneration of the membrane with hot water and the reversal of the crossflow direction; cf. G W Steinhoff,
Brauindustrie
7/89, pages 748 to 750, in particular page 750, right hand column, section “Verschiedene Gerätegrö&bgr;en”(“different sizes of apparatus”).
In particular, the back pressing of filtrate through the membrane also entails problems, in particular due to the covering layer being released thereby only incompletely from the membrane surface. Because as aforementioned, the covering layer is primarily released wherever it offers the least flow resistance to the backwashing process, those parts of the membrane surface which carry a thick covering layer are “disadvantaged by the backwashing” as explained in detail by T Faust et al., in
Chem
.-
Ing
.-
Tech
. 61, 1989, No. 6, pages 459 to 468, in particular page 466.
In all the known processes, the effectiveness of the filtration diminishes with time so that it has not yet been possible to employ the cross flow microfiltration process economically for the clarification of beer. In addition, as the effectiveness of the filtration diminishes due to the growing covering layer, the flow velocities and the pressure across the membrane must be set to very high values in order to attain at all filtration effects which are still acceptable, so that the energy requirements become very high. Due to the reduced filter effectiveness the life expectancies of the membrane filters used are likewise reduced.
In the German patent application P 42 27 225.4 (which is not a prior publication), a plurality of measures have been proposed to prevent or reduce the clogging of the membrane by the ingredients of the beer to be filtered. Inter alia it was there proposed to control the transmembrane pressure and the crossflow velocity of the beer across the surface of the membrane as functions of time, a lower transmembrane pressure and a high flow velocity being set up at the beginning of the filtration and these values being varied in the course of the filtration in relation to a rising transmembrane pressure and a decreasing crossflow velocity. In addition, the filtration is to be briefly interrupted at intervals and the membrane is to be subjected to backwashing, preferably with water during these interruptions. Although it was possible to improve the filtration results by these expedients, the long-term effectiveness of the filtration nevertheless diminished here as well.
SUMMARY OF THE INVENTION
It is a purpose of the invention to create a process for the clarification of beer by means of cross flow microfiltration in which high flux rates can be attained over long filtration periods with simultaneous relatively low energy requirements.
This purpose is fulfilled according to the invention by the features set out in the characterising part of patent claim 1.
Further embodiments of the invention are apparent from the subsidi
Denk Viktor
Gans Ulrich
Sherrer Curtis E.
Shoemaker and Mattare
Wissenschaftsforderung der Deutschen Brauwirtschaft e.V.
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