JPS61249377A - Method of vacuum freeze-drying - Google Patents

Abstract

PURPOSE:To start proper heating, by measuring temperature of a material at fixed time intervals and operating a heater within a fixed time from a point of time when a ratio of a temperature at a time just before a certain point of time to a temperature at the certain point of time becomes <= a set value. CONSTITUTION:The temperature of the material A is successively measured and a ratio of the temperature Tn-1 which was measured and memorized at a time once before a certain point of time to the temperature Tn measured at the certain point of time of DELTAT=Rn-1/Tn is obtained. The value DELTAT is compared with the set value C (C=1 when the lowest point of reduction in temperature by sublimation is standarized), the heat source 2 is operated when DELTA<=C is attained or at a time when a fixed time is passed since it, the heating shelf 2 is heated and the material A is heated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an improvement in a drying method by vacuum freezing of foods and the like.

(Prior Art) Conventionally, drying by vacuum freezing has often been used to dry foods. In this drying method, the item to be dried is pretreated, frozen using an appropriate method, then sublimated under vacuum to remove moisture, and after removing a certain amount of moisture, it is heated with a heater and dried. things will be done. In other words, when a frozen item is placed under a vacuum, a sublimation phenomenon occurs,
If there is no external heat input, the temperature of the item will drop due to latent heat of sublimation. If the degree of descent is rapid, drying is performed quickly, but if the degree of descent is slow, drying is slow and the drying time becomes longer. In order to shorten this drying time, heating is carried out within permissible limits without damaging the properties of the article. Because of such heating, the point at which heating by the heater starts is usually the point when the temperature graph of the item, with temperature on the vertical axis and time on the horizontal axis, becomes almost horizontal. In the technique, the above-mentioned point in time was determined by visually observing the recorded curve of a temperature measurement recorder, and the heater was energized manually. Alternatively, the above-mentioned time point is determined empirically, the heating start time point is set in a timer, and a sequence control operation is performed to energize the heater.

(Problems to be solved by the invention) It goes without saying that the method of visually observing a recorder is time-consuming and complicated, but the conventional sequence control method using a timer allows an experienced person to check the quality of the product before drying. It is based on determining the heating start point in the state. Therefore,
If the properties of the product change or the pre-freezing conditions during pre-treatment change, the heating start point must also change accordingly, but it is not possible to change appropriately in response to such changes in conditions. However, there was a problem in that it was not possible to appropriately determine the heating start point.

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and therefore, it is possible to solve the problems of the prior art without requiring special experience or intuition, and even when the types of articles are different or even when the same article is used, its properties and pretreatments can be changed. An object of the present invention is to provide a vacuum freeze-drying method that can appropriately start heating even if the conditions change.

(Means for Solving All Problems) The vacuum freeze-drying method according to the present invention is characterized by sequentially measuring the temperature of the product under vacuum at regular time intervals, storing the values, and determining the temperature (Tn) at a certain point in time. ) to the previous temperature (Tn-1) (Tn-1/Tn) f, and when the ratio becomes equal to or less than a predetermined value (c), for example 1, Alternatively, after a predetermined period of time has elapsed from that point, the heater is energized and heated.

(Operation of the means for solving all the problems) Therefore, in the method of the present invention, for example, if the heating start point is the point when the temperature graph becomes horizontal in the one-hour temperature relationship, then Tn-1/ The heater is energized when Tn=1 or when a predetermined time has elapsed. Therefore, even if the properties of the product or the pretreatment conditions change, the appropriate heating start point can be automatically obtained.

(Example) Next, the present invention will be described in detail with reference to the drawings. , FIG. 2 schematically shows the apparatus used for carrying out the present invention, in which (1) is a vacuum chamber, and (2) is a vacuum chamber.
(3) is a temperature sensor such as a thermocouple, (4) is a temperature measurement storage device, (5) is a calculation transmitter, (6) is a display device, (power is a power supply Heat sources such as (8) are vacuum pumps. Items to be dried (A)
is placed on a heating shelf (2) in a vacuum chamber (1), and a temperature sensor (3) is attached to the article (A).

When the frozen product (A) is placed on the heating shelf (2), the vacuum pump (8) is activated to create a vacuum and dry it. The vacuum accelerates the sublimation phenomenon and lowers the temperature of the article (A). The temperature of the item is measured by a temperature sensor (3), and the value is stored in a temperature measurement storage device (4) at regular time intervals.
The data is transmitted to, where it is measured and stored. Furthermore, the temperature values are preferably transmitted to a calculation transmitter (5), which is a microcomputer, where each temperature value (Tn-1/Tn
) i calculate. FIG. 1 is a diagram showing the calculation.

The calculation and judgment are performed in the following steps. That is, the first
As shown in the figure, the temperature of an item is measured sequentially, and the ratio of the measured value (Tn) at a certain point in time to the measured value (Tn-1) at a previous point in time is calculated. △T
= Tn-1/'rn (i-calculate. It is preferable to use absolute temperature as the temperature. Next, compare the value ΔT with a value C that is set and stored in advance. If the result is If the temperature is 6>C, the same operation as before is repeated for the temperatures measured one after another.Then, when ΔT≦C or a certain period of time has elapsed thereafter, a signal to start heating is sent. , the display device (6) displays the start of heating.At the same time as this display, the heat source (
A force is applied to send heat to the heating shelf (2) to heat the item.

After issuing the signal transmission instruction, the temperature of the item (A) continues to be measured and stored, but the calculation is discontinued at that point.

In the temperature-drying time graph, heating is often started based on the horizontal point, that is, the lowest point of temperature drop due to sublimation, so usually C = 1, but in some cases it may be earlier. Alternatively, the following may be used as the standard; in that case, the value of C is not necessarily 1 because it becomes C minus 1 or c minus 1.
There is no need to limit it to.

Figure 5 and Figure WC4 show vacuum freeze-drying data. If C = 1, the example in Figure 5 reaches the Pl point in about 35 minutes after vacuum loading, and then Tn-1 /
Tn=1, and heating by the heat source (7) is started from that point on. Then, after about 8 hours after the start of heating, the moisture content of the product becomes about 6 degrees, and after that it follows a parallel line. Also,
In the example shown in Figure 4, the temperature reaches 22 points in about 45 minutes after the vacuum load, and Tn-1/Tn = 1. At that point, heating is automatically started, and the moisture content of the product disappears in about 5 hours after heating. It will cost 2 to 5 yen.

(Effects of the Invention) As described above, according to the present invention, there is no need to set the heating start time based on experience, and the optimum heating start time is automatically determined depending on various factors and conditions of the item to be dried. It will be done. Therefore, heating can always be started at the optimum time without operator experience or continuous observation of the recorder, which not only improves thermal efficiency but also improves the quality of the products in the drying layer. .

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the calculation process of the method of the present invention, Fig. 2 is a diagram schematically showing the apparatus used for carrying out the invention, and Figs. 6 and 4 are data diagrams of vacuum freeze-drying, respectively. . In the figure, 1... vacuum drying chamber, 2... heating shelf, 5...
Temperature sensor, 4... Temperature measurement storage device, 5... Calculation transmitter second flash l 2 Fig. 5 Fig. 4

Claims (1)

[Claims] In a method of freezing an item to be dried, sublimating moisture under vacuum, removing a certain amount of moisture, and then heating and drying with a heater, the temperature of the item is sequentially measured at regular time intervals, and The value is memorized, the ratio of the temperature at a certain point to the temperature just before that (Tn-1/Tn) is calculated, and when the ratio becomes equal to or less than a predetermined value (c), or A vacuum freeze-drying method characterized in that the heater is energized after a certain period of time.