CA1059823A - Method and apparatus for reducing the temperature of bakery products - Google Patents

Abstract

METHOD AND APPARATUS FOR REDUCING
THE TEMPERATURE OF BAKERY PRODUCTS

Abstract of the Disclosure Method for reducing the temperature of bakery products immediately after the discharge thereof from the oven, by means of vacuum. The bakery products are first subjected to a substantially linear pressure reduction as a function of time at a rate of not more than 60 mm Hg per second through at least half of the total pressure drop employed. The pressure reduction rate is then allowed to increase substantially for terminating vacuum treatment.
Apparatus for carrying out the method comprises at least one vacuum chamber adapted to be connected to a source of vacuum through a vacuum conduit and a valve, and a closeable opening for bringing bakery products into and out of the chamber.
In the vacuum conduit in parallel to a servo-valve serving to applying full vacuum effect from the source of vacuum during said remaining portion of the total pressure drop, there is inserted a by-pass conduit having a permanently open flow cross-section adjusted to give said substantially linear pressure reduction.

Description

~- l'h~ inv~nl~on ganerally rela~e~ ~o ~ me~ho~ ~nd an apparatu~ for reducing the t~mperatuxe oE ~akery product:~
immediately a~ex the di~cl arge thereo~ rom the baXing ov~n.
A pa~icularly in~ere~ting :eorm o~ ba~ce;ry pr?du~t~
~n ~his conrlec~lon is br~ad~ ~he last 3tage o the baking ;~ proce~s oiE a loaf of bre~d take~ place i~ an o~l~n ha~ring 1:emperatu~e ~rom 200 to 270C with a baklng tim~ wh:~h ~rarie~
Xrom 45 minute~ to ao ~nlnu~ dep~n~ing; upon ~he tet~era~ure and the cros~-sec~i~n o~ the ~oa s:~ b~eadi ~he ~ru~ o~
t}le loa~ has a ~empera~u~e o~ a~out 95C at ~he- termination of ~i the bz~in~ tlme, whereas the ~emperature o~ the crust ~ :
a}?out 15~C, ~h~ ~rmer tempera~u~e having been ra~her con- :
~taht during the las~ part o~ the bakin~ time becau~e o .'1 evaporation of ~he moisture conter~t in the loa~ o~ breadO
For a n~er o di~ferexlt rea~ons i~ has been co~non in later time~ to wrap bakery products, ln particular brea~, in bag~ for distr~butlon and ~al~
the loave# are packed ~irectly rom ~e oven the : .
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bag canno~ be clo~ed ~ ce the vapour rom the loaf cannot ~ind any path o e3cape and conde~ses on tle inner s~de of th~ bag~ q~his makes the bag ~o~. I a bag of pla~ic material i8 used, t~e ~3urace o~ ~he loa~ of bread will be ~o~ened by the wa~er. In the ca~3 of bread fox which a cr~sp ~rust is a ~al~ty cx~e~iusn (wheat bread~, care should be taken durlng packing o~ the warm loaves tha~ the open bag with it~ con~ent i8 put in an upright position ~o that easy vapour e~cap2 i8 ~ecured. The use o~ plastic material~ for - ~

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packi~g bread type3 having a long ~helf life ox good Xe~ping ~ualltie~ ~w~vle meal bread3 is not po~sible unles~ the loave~ are cooled in be~orehand. Bakers who have ~ound advantageous to ~ell whc:le meal bread in clo~ed bag~ of :~
pla3~ic materlal, therefore m~st provide for t~e cooli~ o~ :
the ltiaves c)f bread a~ lea~t ~or one hour be~ore pac~ing, , e~ther by loading bhem on æhelf c:arr~ge~ being roll~3d in~o large cool;ing hall~, o~ by mean~ o:E a co~v~yor system which take~ the :Loave~ on a round trip las~ g an hour or E~09 Su~h arrahg~me~ o are very lab~ur~ sum~ng andi'or re~ui~b lar~e i~vesl~ment~
Coollng o~ the -~oave3 o ):~read ln the abov~3 arrange-me~t takes place a~ a co~illation o~ a) radiation, b3 corlvec-tion and c) evaporation, I a high reiative humidi~y is main-~ained ln the cooling ~pacet the evaporation will be lower, wh~ch mean~ tha~ the lo~s of -breald welg1~ is reduced, wh~h of co~r~e, i9 o~ portance. ~he reduced 108g, however, must b~ ~een in rela~ion to ~he e~cpen~e~ ~n the ~orm o~ labo. r, time and capital which ha~3 been requirea ~r~ oraex to obtain thi~ re~ult.
~ t i~ known ~hat cooling of bzlkery product~ can be ei~ected by mean~ o~ vacuum t~eatmen~, which i~ d~scribed ih "'I'he E~a~er~ Dige~t", October 1949 and in "~rhe Arkady Revle~", ~-Volume 49, no~ 2, 1~73. ~e pr~3viou~y described method~ for the vacuum cooling of b~ead, however, have not bet3n completely ~ucce~sful and in parltlcular hav~3 not made it poa~ le ~o obtain a maxlmum of proces~lng~ capacl~y with rea~ona~le in~tallat~o~.

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59~323 and operation expenses for the necessary equipment. An impor-tant requirement to the method is also that the vacuum treat-ment must not incur damage to the structure of the bakery pro-duct, in particular the surface or crust thereof. This repre-sents a serious problem which for the first time has been solved with the present invention in so far as cooling with large capacity is concerned.
As in many mass production processes the key to an economic and effective production is found therein that the time period of treatment in each process step is reduced to a minimum. For the vacuum treatment of bakery products a vacuum ~-chamber is necessarily required, and it is an essential pre- ~ -requisite to this invention that the vacuum chambers employed have a comparatively small volume. This makes it possible with a moderate pumping capacity in the vacuum system to apply short treatment times in these chambers, whereby thQ operating rate and thus the production capacity will be high. ;
According to the invention it has been found that a short vacuum treatment time makes it necessary to keep close -~
supervision and control of the pressure variation in the cham-ber. Thus, according to the invention it is essential that the bakery products are first subjected to a substantially linear pressure reduction at a rate of not more than 60 mm Hg per second ak least through half of the total pressure drop employed, and that the pressure reducing rate is then allowed to increase substantially for finishing vacuum treatment.
Although the minimum rate reduction for the first pressure re-duction is not critical, it is desirable that the pressure re-duction and therefore the cooling be achieved as quickly as possible. Thus, a preferred value for the minimum rate reduc-tion in the first stage is 10 mm Hg per second.

. , ,", , ~5~Z3 Thus according to one aspect of the invention there is provided a process for reducing the temperature of hot bakery products, immediately after the discharge thereof from an ove~
by vacuum, the process comprising the steps of: subjecting bakery products, immediately after the completion of baking and discharge thereof from an oven, without subjecting the bakery products to an initial air cooling operation, in a first pressure reduction which is substantially linear as a function of time at a rate of not more than 60 mm Hg per second; and then subjecting the bakery products to a second pressure reduction at an increased rate, and reducing the pressure to a value corresponding to the saturation vapour pressure at the desired temperature of the bakery products~
the reduction of pressure during the first pressure reduction comprising at least half the total pressure reduction of the .
firs~ and second pressure reductions.
If 50C is regarded as a desired loaf temperature, this can be obtained by putting the loaf in a chamber in which the prèssure is reduced to a value corresponding to the vapour pressure at 50C. Water having a higher temperature than 50C
will boil at this pressure. The heat bound by the boiling is ; taken from the loaf. In practice the cooling follows the rate of pressure reduction. As mentioned above, however, it is ;~ shown in connection with this invention that there is a prac- ~`
tical limit to the pressure reducing rate. If the rate is too ; high, damage will be caused to the loaf because of the rela-tively large amounts of vapour released.
According to another aspect of the invention there is . ~
provided an apparatus for reducing the temperature of hot bakery products, immediately after the discharge thereof from ~;~
an oven, the apparatus comprising: a vacuum chamber posi-~ -5 :, d ' tioned to receive bakery products immediately and directly from an oven; means for connecting the vacuum chamber to a vacuum sourc to reduce the pressure therein; first con-trol means, connected to the connecting means, for controlling the pressure in the vacuum chamber to provide a first pressure reduction which is substantially linear as a function of time at a rate of not more than 60 mm Hg per second; and second control means~ connected to the connecting means, for con-trolling the pressure in the vacuum chamber to provide a second pressure reduction at an increased rate.
An embodiment of the invention will now be described by way of example with reference to the drawings in which:
Figure 1 shows a diagram of the pressure variation during vacuum treatment according to the invention, and Figure 2 schematically shows a vacuum chamber with associ- :
ated equipment for cooling bakery products, in ~;
particular bread.
The pressure reducing process shown in Figure 1 takes place in two stages from a point A corresponding to atmos--5a-~., - ~S93~3Z3 pheric pressure. The first stage runs substantially linearly from the starting point at A to a point s during about 12 seconds, under which about 60 ~ of the total pressure drop ; employed is traversed, i.e. from about 760 to about 373 mm Hg. Thls linear pressure drop can adequately be provided ~ for by means of pressure equalization through a conduit I having a cross-section restriction, for instance a nozzle l of about 5 mm diameter. This device will be described more closely below. Whereas during the first pressure reduction ¦ 10 stage between the points A and B it is of great importance that the rate of pressure reduction does not exceed a certain value depending among others to a certain degree upon the type of bakery products being treated, the remaining portion ;
of the pressure drop can be effected without such limitation.
This appears from the curve of Figure 1, which from the point B falls off with substantially greater inclination than during the first portion of the pressure reduction. As usual in such pressure equalization processes the curve will by and by flatten out and the treatment is according to the invention terminated at a point C after a total treatment time of about 20 seconds, somewhat more than 80 ~ of the original pressure ;
~ having then been removed. The terminating pressure shall correspond to the vapour pressure at the desired temperature after the vacuum treatment. The values shown in the diagram -: ~
of Figure 1 relate to a temperature reduction to about 54C
corresponding to a vapour pressure of about 0.15 kp/cm2 or 85 % vacuum. This corresponds to 115 mm Hg in a normal atmosphere.

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5~ ~ ~3 t~hen treating 8 loave~ o~ brea~ s~m~ltaneou~ly (a~ in~iaated by way o~ ex~mple in ~igur~ 2), t~a following igures can serve to illu~trate tha methods A~ter baking, th~ weight o~ :
8 loaves is about 6,25 kg of which 37 % i~ water. At full balance between the vapour pres~ure o~ the water content and the am~ient atmo3phere the evaporated water will ~orre~pond to the cool~ng of the loave~ ~om ~ ~ to ~C.
~ al~ tbe amount or preerably 6~ % of the pressure drop shall be linear in orde~ tha~ t~e vap~ur developed in the loaf o bread shall be able t~ escape.th~ouyh the natural pores o~ ~he cru3t at a pre~sure di~renae w~is~h aoes not b~ealc the crustO ~he pres~u~e rei~uaing velo~ f shall be lowe~ than 6b n~ g per ~econd, ~ ich i~ ~he p~eu~e ~aduc~ng proce~s exam~le o ~igure 1 corre~ponds to the per~orming o~ ;
the l~near p~rtio~ of the pressuxe raduction during not le~
than ~ ~econds. The term~nating pr2s~ure and the linear port~on o~ the process shall be adju~table.
A schemat~c and sim~ ied example o~ an appar~tus according t~ th~ invention i5 shown in ~isure 2. Th~ appa-ra~us is ba~ed on t~e co~pera~ion wi~h an ~ven ~r~m which the loave~ o~ bread are pushed out in group~ or row~ of 7 - 8 loaves in parallel or tran~versally to ~he longitudinal direction of khe oven at an angle of gOv by mean~ o a con-veyor or a~ ~jac~or as~ociated w~th the oven. The loa~e~ 2 are conveyed in the~r longitud~nal direct~on ~nto a cylindri-cal vaauum chamber 1 w~ich can be clo~ed with a cover 3 to w~ic~
there i8 connected a vacuum conduit 4 with a~sociated valve~

8~3 and cc)nnection~. More ~peci~c~ly, this vacuum 8y#tem con-sist~ o~ a branch piece 10, a s~ort vacuum conduit 9 and a servo-valve 6 which t~rou~ an additional vacuum conduit 5 3erve~ to cc)nnect the vas~u~n ~haniber 1 to a vacuum pu~p or an-other ~ource o~ vacuwn which 1~ not s~own irl the drawing. ~,h pa~allel to ths ~ervo-valve ~ ~here i3 provided a by-pass con d~it 8 wh~ch has a calibra~d or adjustable flc~w cros~-sec~ioaa bein~ re~tricted in relation to the open i~low crog~-~ection oi~ ~ervo-valve 6, ~o a~ ~o give the ~lower near l~o linear pressure redu¢t~on at the beginrling o~ the vacuum traat~nent. - :~
For ad~stnl~3nt or control o~ the :Linear ~e~ e reduction rate l~h~3re i~ ln~erted a control ~ral~e 7 isl the by-pass conduit~
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For terminatirg the vacu~ rea~me~t a magnet val-~re 12 is connectea to ~he branc:h piece lO ~hrough a condu~t ll :for allowing atmospheri~ pres~ure ~o enter th~ cha~er 1. For this pu~o~e ~e magnet valve 12 :i~ connecited to the amiblenlt ., . :
a~o~ph~re ~hrough a conduit 13 peeially during s~arting up o~ the proce~q th~
vapo~r ~rom ~he ba~ery product~ may condan~e ln the cylindrical chamber. In prac~ice it may t~erefore be an advantage to pro- :
vlde mea~3 or p~eventing condensed water from reaching the cru~t on the product~ being ~rea~edO For hygienic rea~ons, however, it may be de~irable to a~oid inlays, in~ert~ or the llke in th4 ~hamber ~or th~ purpo~e. CondensatLon must i~
das~ be pxevented by heating tha chamber~ ~his can be done :~
by ~uitable means, for instance by radiant heat.
}n connection with the dr~wing there 18 no detailed ~5~ 3 illu~tration o~ mec~hani~m~ ~or opening and clo~ing ~he cover 3 on the chamb~ n ~i~ure 2, but the n~c~s~ry stxucture or obtaining these un~10ns will be near at hand to a per~on ~ki~led in the art.

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Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for reducing the temperature of hot bakery products, immediately after the discharge thereof from an oven, by vacuum, the process comprising the steps of:
subjecting bakery products, immediately after the completion of baking and discharge thereof from an oven, without subjecting the bakery products to an initial air cooling operation, in a first pressure reduc-tion which is substantially linear as a function of time at a rate of not more than 60 mm Hg per second; and then subjecting the bakery products to a second pressure reduc-tion at an increased rate, and reducing the pressure to a value corres-ponding to the saturation vapour pressure at the desired temperature of the bakery products;
the reduction of pressure during the first pressure reduction comprising at least half the total pressure reduction of the first and second pressure reductions.

2. A process as claimed in claim 1 wherein the first pressure reduction is at a rate of from 10 to 60 mm Hg per second.

3. A process as claimed in claim 1 or 2, wherein the desired temperature is suitable for the packaging of the bakery products.

4. A process as claimed in claim 2, wherein the reduction of pressure during the first pressure reduction corresponds to 60% of the total pressure reduction.

5. A process as claimed in claim 4, wherein the first pressure reduction is completed in twelve seconds and the total pressure reduction is completed in twenty seconds.

6. A process as claimed in claim 1 or 2, wherein both the first and second pressure reductions are achieved by use of a single vacuum source.

7. A process as claimed in claim 1 or 2, wherein the second pressure reduction is non-linear as a function of time.

8. A process as claimed in claim 1 or 2 wherein the hot bakery products are vacuum cooled, immediately after the discharge thereof from an oven, to a temperature at which the bakery products are to be packed, and for forming the bakery products with a relatively thick and crisp crust without bursting the crust, the bakery products sub-jected to the first pressure reduction, immediately after the completion of baking are discharged from an oven at atmospheric pressure, thereby preventing bursting of the crust of the bakery products; and the second step comprises subjecting the bakery products to a second, non-linear pressure reduction to the temperature at which the bakery products are to be packed.

9. An apparatus for reducing the temperature of hot bakery products, immediately after the discharge thereof from an oven, the apparatus comprising a vacuum chamber positioned to receive bakery products immedi-ately and directly from an oven;
means for connecting the vacuum chamber to a vacuum source to reduce the pressure therein;
first control means, connected to the connecting means, for controlling the pressure in the vacuum chamber to provide a first pressure reduction which is substantially linear as a function of time at a rate of not more than 60 mm Hg per second; and second control means, connected to the connecting means, for controlling the pressure in the vacuum chamber to provide a second pressure reduction at an increased rate.

10. The apparatus as claimed in claim 9 wherein the first control means is for controlling the pressure to provide the first pressure reduction at a rate of from 10 to 60 mm Hg per second.

11. An apparatus as claimed in claim 10 wherein the connecting means comprises a conduit.

12. An apparatus as claimed in claim 11 wherein the second control means comprises a servo-valve in the conduit, the servo-valve having a cross-section therethrough sufficient to apply the full effect of the vacuum source, and the first control means comprises a by-pass conduit connected to the conduit in parallel to the servo-valve, the by-pass conduit having a cross-section restricted as compared to the cross-section of the servo valve.

13. An apparatus as claimed in claim 12, further comprising control valve means in the by-pass conduit for controlling the rate of the first pressure reduction.