referring to fig1 through 9 , wherein like reference numerals refer to like components in the various views , there is illustrated therein a new and improved oscillating flow platform , generally denominated 100 herein . in accordance with the present invention , fig1 . is an exterior side elevation of oscillating flow platform 100 . the platform comprises a support frame or stand 110 to which trough 160 is mounted by four pivots legs 101 . the trough is tilted downward from grape receiving end 160 a toward an open mouth 166 . the trough has an aperture 163 that spans the midsection of the bottom surface for receiving a screen 500 . thus , in a winemaking operation oscillating flow platform 100 receives grape berries at end 160 a after de - stemming . as trough 160 oscillates in the plane of fig1 , about the four pivot legs 101 , the de - stemmed grape berries and mog arriving from the de - stemmer are agitated as they flow downward with gravity toward open mouth 166 . open mouth 166 is preferably tapered inward , as shown in fig4 , so that the still oscillating berries are directed into the next conveyor , storage or process vessel in the winemaking process . the agitation induced by the oscillating trough 160 results in multiple opportunities for the mog , raisons and shot berries to contact and pass through screen 500 . in contrast , the larger whole berries , being bigger than the slots in the screen 500 , pass over it and exit the trough 160 at open mouth 166 . as will be further described with respect to fig5 - 8 , the screen 500 is configured such that whole berries pass over the screen while the majority of the undesirable mater falls through the screen . as a preferred embodiment , the trough has a solid area 161 for receiving de - stemmed grapes before entry to screen area . initially dispensing grape berries on the solid area 161 has been discovered to result in a lower yield of juice being produced by the rupture of berries during the separation process . while the percentages of berries that rupture during the separation process is small , it can be significant for winemakers that plan to use a carbonic maceration process during the initial stages of fermentation , wherein fermentation initially occurs within the whole , un - ruptured berries . further , avoiding the rupture of berries also minimizes the possibility that a portion of the grape juice will become oxidized before the start of fermentation . the matter passing through screen 500 is directed by funnel trough 106 , placed there under , into a removable open box - like catch basin 108 . catch basin 108 has a secondary screen 560 its bottom surface . secondary screen 560 has a finer mesh pattern than screen 500 so that solid mog is now retained , but grape juice generated from broken berries passes through , to be collected in the underlying secondary trough 167 . secondary trough 167 has a solid bottom surface that tapers toward a drain hole 168 and connected drain pipe 169 . thus , any juice produced by rupturing the grape berries , either during the de - stemming process or separation of mog in oscillating flow platform 100 , is readily removed and collected via a hose line or bucket placed under drain 168 . catch basin 108 rests on secondary trough 167 so that it is readily removed therefrom to periodically disposed of the solid materials separated from the grape berries by screen 500 . it should be appreciated that catch basin 108 need not be limited to a discrete fixed member as illustrated , but in other embodiments may take the form of a screen conveyer belt so that that mog , raisons and shot berries are continuously removed from the apparatus , before they have a chance to accumulate as they would in the discrete catch basin 108 illustrated herein . trough 160 is oscillated about the four pivot legs 101 via motor 120 and drive assembly 125 . the upper ends of the pivot legs 101 are connected to trough 160 via upper bearings 164 , whereas the lower ends of the pivot legs 101 are connected to trough 160 via lower bearings 102 . the upper 164 and lower 102 bearing structures are preferably bushings , but are alternatively a roller bearing , a ball bearing and the like . the motor 120 and drive assembly 125 are mounted to support frame 110 just below the upper end 160 a of the trough 160 . the oscillation frequency of trough 160 is readily varied to suit the characteristics of the grape variety being treated by modulating the speed of motor 120 via frequency drive controller 125 . frequency drive controller 125 allows the user to control the speed of electric motor 120 by modulating the applied current . as shown in further detail in fig3 a and 3b , drive assembly 125 also comprises a drive shaft 140 supported for free rotary motion within a pair of block bearing 142 , which are mounted to frame 110 . a drive belt 130 is mounted at one end to surround the belt sheeve 132 attached to the motor drive shaft 121 . the opposite end of drive belt 130 is wrapped to surround drive shaft belt sheeve 134 . thus , the rotation of motor 120 rotates drive shaft 140 via drive belt 130 . laterally disposed about the center of drive shaft 140 is a cam 150 . the cam 150 has a cam follower 155 attached , which extends perpendicular to drive shaft 140 . the cam follower 155 is coupled to the cam 150 to oscillate back and forth along its principle axis as the cam surface is displaced in the same direction with every rotation of drive shaft 140 . the other end of the cam follower 155 is attached via the rotary coupling of central bearing block 162 ( shown in fig1 ) to the bottom of trough 160 , just forward of screen aperture 163 . thus , as the cam 150 rotates eccentrically with respect to drive shaft 140 , the cam follower 155 is driven to oscillate in the plane of fig1 and likewise drives trough 160 to oscillate in the same plane via pivoting legs 101 . still referring now to fig3 a and 3b , further details of the preferred embodiment of the drive system 125 will now be described . drive shaft 140 has at each end , outward of cam 150 and block bearings 142 , a pair of drive shaft counterweight assemblies 145 . an external side elevation of the drive shaft counter weight assembly 145 is shown in fig3 b . it should be appreciated that support stand 110 is attached to or rests on the ground via stand feet 105 . the stand support feet terminate in rubber damping pads 104 which contact the supporting floor or ground surface 10 to minimize vibration transmitted from the oscillatory motion of the trough 160 . however , it has been discovered that the counterweight assembly 145 vastly minimizes such vibration . in the most preferred embodiment , the counter weight is configured to provide a non - uniform radial distribution of weight with respect to the axis of drive shaft 140 . the weight is distributed such that the center of gravity of each counterweight assembly 145 is directly on the opposite side of drive shaft 140 from cam 150 and cam follower 155 . in fig3 b the drive shaft counterweight assembly 145 is shown as composted of two disks segments ( 145 a and 145 b ) and two annular segments ( 145 c and 145 d ) secured together by common bolts 146 bolted together . however , each counterweight assembly can also be constructed as a monolithic component . each counterweight assembly 145 is preferably secured to the end of drive shaft 140 as shown by end bolt 147 . the non - uniform radial distribution of counter weight 145 is provided in this embodiment by the stacking two wedge shaped segments 145 d and 145 e . the two wedge shaped segments 145 d and 145 e affixed to the other portions of counterweight assembly on the end of drive shaft 140 such that center of gravity of the counterweight assembly 145 with respect to drive shaft 140 is opposed to the center of gravity of cam 150 . the preferred masses of counterweights 145 a - e are 6 , 3 , 3 and 1 . 5 pound respectively , for a total mass of 13 . 5 pounds on each side of drive shaft 140 . reducing vibration of oscillating flow platform 100 not only reduces noise to nearby workers , but also greatly reduces the tendency for the unit to move during use , and is expected to generally extend the useful product life . without wishing to rely on theory , it is believed that as vibration is reduced with counterweight assembly 145 there is also a more efficient coupling of the rotary motion of motor 120 , into the oscillatory motion of trough 160 , increasing the potential throughput of whole berries in trough 160 while maintaining the high separation yield of undesirable material through screen 500 . the optimum construction and function of screen 500 is more fully described below with respect to fig5 - 9 . however , it should be appreciated that one method of mounting screen 500 in aperture 163 is with the long axis of the slots 502 parallel with the principle axis of the trough 160 ; oriented to incline downward with the trough 160 . an alternative method of mounting a different screen , shown in fig9 , results in the long axis of the slots 502 ′ oriented perpendicular to the principle axis of the trough 160 . referring now to the first embodiment shown in fig5 , screen 500 has a rectangular frame 530 . inset and connected to each interior corner of frame 530 are four solid rectangular mounting corners 540 . each mounting corner 540 has a stud 541 for receiving a wing nut assembly ( not shown ) for secure attachment to the trough 160 to fill aperture 163 . the remainder of the screen 500 within frame 530 is formed from an interconnected array of triangular shafts and wires . the spacing between the shafts is less than that between the wires to define the array of rectangular slots 502 . thus , connected to opposing sides of the frame 530 is a parallel array of triangular shafts 510 , each shaft being oriented so that sides of equal width define a common plane 505 at the entrance side of screen 500 , as shown in section vi - vi ′, in fig6 . the wires within parallel array 520 are connected at the ends to other pair of opposing sides of frame 530 . each wire in the parallel 520 is connected to each of the triangular shafts in array 510 that it traverses so as to stabilize the entire parallel ray of shafts . as shown in fig7 , corresponding to section line vii - vil ′ in fig5 , it can be seen that each wire connects to the traversing triangular shaft at the apex thereof , opposite the side that defines a portion of plane 505 . in the embodiment of screen 500 in fig5 - 9 , it is preferable that the edge to edge spacing of the triangular shafts at the upper surface , w , within screen 500 is about 0 . 25 inches , with the orthogonal wires separated by a distance , l , of about 1 . 75 inches . the sides of each triangular shaft preferably has a width of about 0 . 25 inches wide . the wire preferably have a diameter of about 0 . 25 inches . thus , in this preferred embodiment screen 500 consists of slots 502 having an aspect ratio of l / w . l / w is preferably greater than about 3 , and more preferably greater than about 4 , and most preferably at least about 6 . in the preferred embodiment of the oscillating flow platform 100 screen 500 is mounted with the leading edge ( that is the side closer to grape receiving end 160 a ) depressed or at least level with the bottom of the trough and the trailing edge ( the side closer to open mouth 166 ) above or at least level with the interior bottom of the trough 160 . the screen construction shown in fig5 - 9 has several surprising advantages for separating grapes . from the interior of the trough 160 , plane 505 , the screen appears to the arriving grape matter as a series of slots . the slot spacing w is narrow enough to return ripe whole berries , yet let smaller raisons , shot berries and most forms of mog pass through . it should be noted that as the wires 520 are connected to the triangular shafts 510 near the lower and downward faxing apex , this adjacent area is wider , having a width , w , as shown in fig7 . not wishing to be bound by theory , it is currently believed that one reason for the higher throughput of screen 500 is that once mog particles passes through aperture 501 , they are unlikely to re - enter in the opposite direction . further , the size and spacing of the triangular rods and wires is such that high aspect ratio mog , ( such as stems , twigs and insects and the like ) will not collect on these members , but rather fall downward toward secondary screen 560 for catching separated mog . likewise , it is believed that the inverted shape of the triangular shafts 510 , with the narrow opening w at the upper or entry surface at plane 505 makes it unlikely that matter vibrating free or hitting wires 520 will reverse direction and pass back up above plane 505 into trough 160 . although the wires 520 are a locus for the potential buildup of matter that passes through the gap w ( between triangular shafts in plane 505 ), the tendency toward build - up is reduced as the inverted triangular shape of the shafts 510 provides a wider gap , w , and hence more space for such matter to tumble free of the wires 520 due to the oscillation induced vibration of the matter as it enters and then traverses screen 500 . it should be appreciated that for some varieties of grapes it has been discovered that the orientation of the rectangular slots 502 ′ in screen 500 , as shown in fig9 , may be preferable for removing mog and other undesirable components . screen 500 has a rectangular frame 530 . inset and connected to each interior corner of frame 530 are four solid rectangular mounting corners 540 . the remainder of the screen 500 within frame 530 is formed from an interconnected array of triangular shafts and wires that as in the embodiment of fig5 , to define the slots 502 ′. however , the array of triangular shafts and wires are now reversed in orientation with respect to the long and short sides of screen 500 . that is the parallel array of shafts 510 is now oriented parallel to the short axis of screen 500 and the parallel array of wires is oriented in the transverse direction or parallel to the long axis of screen 500 . the spacing between the shafts is less than that between the wires to orient the rectangular slots 502 ′ with their longer axis parallel to the shorter side of screen 500 . while the invention has been described in connection with a preferred embodiment , it is not intended to limit the scope of the invention to the particular form set forth , but on the contrary , it is intended to cover such alternatives , modifications , and equivalents as may be within the spirit and scope of the invention as defined by the appended claims .