The deterioration of coffee, i.e. the loss of a "fresh" or palatable flavor and aroma, is primarily caused by oxidation and evaporation. In a conventional 8-12 cup coffee decanter, deterioration is generally so complete within one or two hours, depending on the rate of consumption, as to render the remaining coffee undrinkable.
The role of oxidation, alone, in deteriorating coffee flavor is obvious to anyone who drinks coffee from a Thermos. When the Thermos is first opened, whether after one or several hours, the coffee tastes perfectly fresh. If the Thermos is resealed with a small amount of coffee remaining therein, such as a half cup, it rapidly deteriorates as evidenced by the poor taste when it is consumed, say, one hour later. There was obviously no significant evaporation from the sealed Thermos but fresh air was admitted at the time the first cup was poured.
The deteriorating role of evaporation is even more obvious as the coffee solution is concentrated by evaporation.
The concept of extending the "pot life" of coffee, i.e. that time period during which it retains the flavor and aroma of freshly brewed coffee, by substantially eliminating its exposure to atmosphere while yet retaining the ability to pour coffee in conventional fashion was introduced by applicant's prior U.S. Pat. No. 3,974,758. In a pour type coffee decanter, the patented concept involves sealing the main body of contained coffee with respect to atmosphere. The top of the decanter is sealed by a movable follower, such as a bellows or bag, and that coffee contained within the lower end of a small diameter pour spout opening into the coffee decanter adjacent the bottom thereof serves as a liquid seal between atmosphere and the main body of the decanter contained coffee.
The result is that the only oxidation that can occur takes place at the upper coffee level in the pour spout. By keeping the cross section of the pour spout sufficiently small, that quantity of coffee that is oxidized and subsequently finds its way through the liquid seal to the main reservoir of contained coffee is negligible over the first 4-8 hours depending upon the cross section of the pour spout. Similarly, the only loss to atmosphere that can occur by way of evaporation is at the small upper coffee level in the pour spout since a state of equilibrium inherently exists across a gas/vaporizable liquid interface in a sealed container.
Stated differently, the patented concept involves pouring from the bottom of the decanter while keeping the top of the decanter sealed with a movable follower maintaining atmosphere pressure on the coffee so that it can be poured without creating a vacuum lock.
In applicant'copending application, Ser. No. 219,461, filed Dec. 23, 1980, is disclosed method and apparatus whereby the movable follower may be eliminated and coffee readily dispensed while yet retaining substantially all the advantages of a totally sealed decanter, albeit over a shorter time span, by providing vent means of such small dimension that the vapor pressure of a quantity of contained coffee within the decanter exceeds atmosphere pressure. The result, as explained in the aforesaid copending application, is a vapor seal across the vent means that precludes the ingress of air at all times except when coffee is actually being dispensed through the pour spout. The volume of entry air that occurs during pouring is, of course, negligible as compared with that volume which enters a conventional open decanter over a period of from one to several hours.
A concomitant, and significant, consequence of the restricted vent means is greatly reduced evaporation as compared with a conventional decanter from which the vapor may freely escape.
Thus, where vapor may freely escape, as from a conventional decanter, equilibrium across the gas/liquid interface is never attained and evaporation may proceed to completion. Conversely, in a closed system, partial pressures of the coffee vapor will increase until a state of equilibrium exists at which time for every molecule escaping across the liquid/gas interface in gaseous form another is returning from the gaseous to the liquid form at which point no further liquid volume loss to evaporation occurs. The latter is what occurs in the patented process where the space above the decanter contained coffee is totally sealed.
An analogous result is achieved by the restricted vent means disclosed and claimed in the aforesaid copending application which, in effect, imposes a back pressure on the contained gaseous phase so that equilibrium is approached with the result that percentage return from the gaseous to liquid phase approaches that of escape from liquid to gaseous. The result, over a period of up to about 4-6 hours depending on the rate of depletion by dispensing, is negligible coffee volume loss to evaporation. In actual tests conducted with a six cup volume in a twelve cup decanter with the coffee maintained at 175.degree. F. and a single 1/16" diameter vent hole; loss to evaporation was less than one-third cup over a five hour period as contrasted with a two and one-half cup loss to evaporation from a conventional decanter. It will be obvious that the smaller the vent means the closer the approach to equilibrium and the lesser volume loss to evaporation.
In summary, concerning the vent means which for the present explanation will be assumed as a single pin hole in an otherwise sealed top of a coffee decanter which decanter includes a small diameter pour spout opening into the decanter immediately adjacent the bottom thereof; the vent means is necessary to permit the pouring of the coffee, in the absence of any movable parts, without developing a vapor lock. Regarding its role in reducing oxidation, the vent means must be of sufficiently small cumulative area to produce a back, or superatmospheric, pressure within the decanter to prevent ingress of air by a vapor seal across the vent means when the decanter is in the upright, or non-pouring, position. The role of the restricted vent means in reducing volume loss through evaporation is that of causing the partial pressures across the gas/liquid interface to approach equilibrium.
Since the overall purpose of the invention disclosed in the aforesaid copending application is to insure that the entire contents of a coffee decanter may be consumed without having to discard the last few cups because they have deteriorated to an unpalatable state; the importance of having a small diameter pour spout extend to substantially the bottom of the decanter and remain submerged at all times as the coffee level is depleted may be appreciated. Thus, by the time the coffee level has been substantially depleted, as for example to the two or three cup line, both oxidation and evaporation will, if permitted, play a far greater deteriorating role than when a full decanter of coffee is initially made. First, the smaller coffee volume will normally be at a higher temperature than the original filled decanter (assuming a standard, automatic drip coffee maker burner to be used) and as with most other chemical reactions, oxidation is accelerated by increased temperature as is the rate of evaporation. Secondly, deterioration due to oxidation proceeds more rapidly because of the proportionally greater surface area exposure in a small volume while even an equal rate of evaporation produces a far greater proportional concentration in a small, as compared with a large, volume of liquid. If the lower end of the pour spout does not remain submerged as the coffee level is depleted the liquid seal is broken, air reaches the remaining coffee to oxidize the same and the approach to equilibrium across the liquid/gas interface is destroyed allowing evaporation to proceed toward completion. This is why many conventional coffee pots of the electric or stove top percolator type which have outside pour spouts are not suitable for use with the present invention. In all cases they have at least a portion of the pour spout opening into the pot at a level well above the bottom of the pot and as soon as this upper level of the pour spout opening into the pot is reached by the declining coffee level the remainder of the coffee is quickly deteriorated by oxidation and evaporation.
Accordingly, the entirety of the lower open end of the pour spout must be positioned so that it remains completely submerged at all times, with the liquid seal intact, until substantially all the coffee is dispensed, else the primary advantage of retaining the palatability of the remaining coffee is lost. In actual practice, with various 8-12 cup coffee decanters it is more desirable to insure that the liquid seal remains intact, if possible, until the next to last cup is dispensed leaving only one cup subject to the deteriorating effects of oxidation and evaporation. In actual practice it is found that this last cup is usually consumed before it is substantially deteriorated. The foregoing translates into a necessary positionment of the lower open end of the pour spout at such a height above the bottom of the decanter that the entire lower open end of the pour spout remains completely submerged at remaining coffee levels falling generally within the range of 1/6 to 1/4 the height of a full decanter fill level of an 8-12 cup decanter. The range is stated thusly to take into account various pot capacities and configurations though it will be apparent that the lower end of the spout should be as low as feasible.
If the top assembly is to be placed on the decanter after it is filled with coffee then the vent means need involve only a single vent, or pin hole, opening whereas if the top is to be placed on the decanter prior to its placement under a drip coffee maker to receive freshly brewed coffee through a central "vent means", then a second vent opening must be provided to allow escape of displaced air as the pot is filled. It is not the number or the spacing of the vent openings that is critical, rather it is their cumulative area; i.e. their cumulative area must be sufficiently small as to maintain superatmospheric pressure within the decanter when it contains a quantity of hot coffee above, for example, 160.degree. F. Indeed, specific holes need not be formed in the top assembly if the top assembly is so interfitted with the open top of the decanter that vent air can be admitted while precluding the outflow of coffee as the decanter is tilted to "pour from the bottom". Exemplary of the latter would be a screw cap substantially, but not totally, sealed with respect to atmosphere.
As would be expected from the foregoing discussion, the patented concept wherein the decanter is totally sealed by a movable follower extends the "pot life" of coffee over a longer time span than does the "restricted vent means" concept disclosed in the aforesaid copending application. The reasons are:
(1) There is no air indrawn to the sealed container during dispensing to oxidize the decanter contained reservoir; and PA1 (2) The partial pressures across the gas/liquid interface within the decanter reach equilibrium so that there is no evaporative loss to atmosphere
whereas the "restricted vent means" concept limits, rather than eliminates, the deteriorating effects of oxidation and evaporation.