JPH0453474A - Direct heat sterilizing method and equipment therefor - Google Patents

Abstract

PURPOSE:To perform complete and sure heat sterilizing of liquid food by directly mixing steam, measuring a passing time of heated liquid food in a flowing path kept at a high temperature and discharging liquid food having the passing time longer than a fixed time. CONSTITUTION:At first, liquid food is transferred to a steam-mixing device 2 by a feed pump and steam from a steam control valve is directly mixed to heat a fixed sterilizing temperature. Successively, said liquid food is passed through a flowing path kept at a high temperature in a state of kept at a sterilizing temperature and simultaneously passing time of the fluid food in the flowing path 9 is measured. At last, liquid food having said passing time attained to a time longer than a fixed time is discharged to a heat sterilized food-preserving part C.

Description

Detailed Description of the Invention A9 Purpose of the Invention [Industrial Field of Application] The present invention relates to a method and apparatus for direct heat sterilization of liquid foods, and more specifically, to a method and apparatus for direct heat sterilization of liquid foods, and more particularly, to The present invention relates to a direct heat sterilization method for liquid foods, in which the liquid foods are sterilized while passing through a high-temperature holding channel for a predetermined period of time, and an apparatus for carrying out the method.

[Technical background and conventional technology] Steam is directly mixed into the liquid food flowing through a flow path, heated to a predetermined sterilization temperature, held for a predetermined time, and then steam mixed into the liquid food in an evaporation tank. A direct heat sterilization method (hereinafter referred to as the conventional method) that removes a considerable amount of water.Please note that liquid foods processed by this method have almost no microorganisms left in them and are in a completely sterilized state. teeth"
The sterilization method (hereinafter referred to as the ``sterilization method'') and the W (hereinafter referred to as the conventional apparatus) have been widely employed in the food industry. In the conventional method and device described above, sterilization was determined to be poor by controlling and monitoring only the sterilization temperature, and if the temperature was lower than a predetermined temperature, it was determined that sterilization was defective (Supervised by Tomoyoshi Tsugo, "Ichiryu Kogyo J, p. 147. , Chikyu Publishing, 1962).

Figure 4 is an explanatory diagram of a typical conventional device (excerpted from the catalog of Neepy Buoy Co., Ltd. <APV Company). and conventional methods will be explained in detail.

The liquid food to be sterilized is preheated by the preheating device A, then transferred to the injector nozzle (2) by the feed pump (1), mixed with steam flowing in from the steam control valve (3), and heated. It is held for a predetermined time in a holding tube (9) serving as a high temperature holding flow path to be sterilized, and then transferred to an evaporation tank (5) serving as a water removal device. The sterilized liquid food has moisture equivalent to the mixed vapor removed, and is transferred from the evaporation tank (5) to the homogenizer (12) by a discharge pump (11).

The liquid is transferred to a cooling section (13) where it is homogenized and cooled, and then transferred through a switching valve (14) to a liquid storage tank C as a heat sterilized food storage section. The sterilization temperature is the holding tube (9)
The temperature is continuously measured by a thermometer installed in the steam control valve (3), and the temperature is maintained at a predetermined temperature by controlling the opening degree of the steam control valve (3) by a temperature controller (7). If the sterilization temperature falls below a predetermined temperature, the liquid food present in the holding tube (9) is determined to be poorly sterilized, and the switching valve (14) is activated to change the flow path in the direction of B in Figure 1. ) to prevent mixing with liquid foods that have already been sterilized. The liquid level in the evaporation tank is maintained constant by controlling the rotation speed of the rotor of the feed pump 1 by a level controller (10) to increase or decrease the pump discharge amount, that is, the amount of flow into the evaporation tank (5).

In the conventional device shown in Figure 4, it was known that the flow rate discharged from the evaporation tank remained constant because accurate quantitative flow could be maintained by the homogenizer (12) downstream from the evaporation tank. . However, in conventional devices, upstream from the evaporation tank, the level controller (10) only controls the supply amount of the feed pump (1), and the amount of inflow to the evaporation tank (5) and its fluctuations are limited. No consideration was given to controlling fluctuations in the sterilization time due to fluctuations in the flow rate in the holding tube (9) caused by this.

This is considered to be due to the following reasons.

Generally, in the sterilization of liquid foods, the heat killing effect on bacteria is expressed as a function of sterilization temperature and sterilization time (Supervised by Kazuyoshi Aiso,
"Food Microbiology J, p. 148, Ishiyaku Shuppansha, 1976). Therefore, even in the conventional direct heat sterilization device, it is necessary to control the sterilization temperature and sterilization time. The sterilization time was managed as described above.In addition, the sterilization time was handled as follows.In other words, the feed pump (liquid transfer pump) was a constant volume pump with a stable discharge volume. etc., in a steady state, the flow rate of the liquid food flowing inside the holding tube is also stable, and the flow rate does not change much. Therefore, the predicted flow rate of the liquid food inside the holding tube is If the length of the holding tube is set in consideration of the fluctuation range, the passage time (i.e., sterilization time) of liquid food through the holding tube (high temperature holding channel) should be longer than the specified time. .

Based on this idea, the sterilization time was not monitored in the conventional direct heat sterilizer.

[Invention tries to solve! lul! ] However, as a result of detailed analysis of the sterilization method using the conventional direct heat sterilization device, the inventors found that the flow rate in the high temperature holding channel (inside the holding pipe) was higher than previously thought due to the following reasons. It was found that fluctuations were induced.

(a) Even if the feed pump is a positive displacement type, the volumetric efficiency changes depending on the viscosity of the liquid food to be transferred, and the discharge amount fluctuates. This was particularly noticeable when the liquid in the apparatus was changed from water to liquid food at the start of sterilization, and when the liquid in the apparatus was changed from liquid food to water at the end of sterilization.

(b) When sterilization is performed continuously for a long period of time, the blue pressure of the injection nozzle, that is, the feed The pressure in the discharge side flow path of the pump is varied, thereby varying the discharge amount of the feed pump.

(c) Due to the phenomena (a) and (b) above, the flow rate in the high temperature holding channel (holding tube) varied, and as a result, the sterilization time varied.

(d) In the holding tube through which the mixed fluid of steam and liquid food injected by the injection nozzle flows, the fluid pressure is higher than the saturated vapor pressure corresponding to the sterilization temperature. However, when this pressure difference decreases, incomplete condensation of steam (so-called steam venting) occurs within the holding tube.
Liquid food flows at high speed along with incompletely condensed steam, reducing the passage time of the fluid in the holding tube (i.e., the sterilization temperature holding time).
decreased.

Because of the above phenomenon, when sterilizing liquid foods, the sterilization time may be insufficient even if the sterilization temperature is maintained at a predetermined value.

The present invention has conducted intensive research on a method for sterilizing liquid foods using the conventional direct heat sterilization device, and has developed a method for sterilizing liquid foods using the conventional direct heat sterilization device. may fluctuate more than expected,
This was done as a result of the discovery that variations in sterilization time were significantly affected, and the purpose of nH is to provide a method and apparatus that can reliably sterilize under predetermined sterilization conditions.

Means for Solving Purified EWAH of B3 Invention] The direct heat sterilization method of the first invention of the present application involves directly mixing high-temperature steam into a liquid food flowing in a flow path and heating it to a predetermined sterilization temperature. In a direct heat sterilization method in which the heated liquid food is heated and sterilized by passing through the high temperature holding channel while maintaining the heated liquid food at the predetermined sterilization temperature, the liquid food passes through the high temperature holding channel. The method is characterized in that the liquid food whose passage time is longer than a predetermined time is discharged into the heat-sterilized food storage section by measuring the time.

In addition, the direct heat sterilization device of the second invention of the present application includes a steam mixing device that directly mixes steam into the liquid food into the flow path of the liquid food transferred by the feed pump and heats the liquid food to a predetermined sterilization temperature. Attire! and a high-temperature holding channel through which the liquid food heated by the steam mixing device passes while being maintained at the predetermined sterilization temperature, and the liquid food that has passed through the high-temperature holding channel is transferred to a heat-sterilized food storage section. A direct heat sterilization device is provided with a discharge device for discharging, and a passage time measuring means for measuring the passage time of the liquid food in the high temperature holding flow path is provided, and the discharge device is configured to discharge the liquid food through the high temperature holding flow path. A flow path switching valve is provided for discharging liquid food whose passage time in the channel is longer than a predetermined time to the heat sterilized food storage section, and discharging liquid food whose passage time is less than a predetermined time to another location. It is characterized by the presence of

[Function] According to the first and second inventions of the present application described above, the passage time of the liquid food in the high temperature holding channel is measured, and the liquid food whose passage time is longer than a predetermined time is heated. Since the liquid food is discharged to the sterilized food storage section, only liquid food that has been heat sterilized for more than a predetermined time, ie, completely sterilized liquid food, is discharged to the heat sterilized food storage section. Therefore, liquid foods that have not been sterilized for an insufficient time will not be mixed into the heat sterilization storage section.

[Example] Next, a first embodiment of the present invention will be described based on the drawings.

FIG. 1 is an explanatory diagram of a first embodiment of the direct heat sterilization apparatus of the present invention, showing an example in which milk was sterilized.

In Fig. 1, the liquid food preheated by the preheating device A is transferred by the feed bomb 1 (1) to the injection nozzle (2) as a steam mixing device, and steam from the steam control valve (3) is blown into the liquid food. The outlet temperature of the holding tube (9) as a high-temperature holding channel and the flow rate after steam mixing are measured by a flow meter (50) installed in the holding tube (9), and the flow rate is measured as a water removal device. Transferred to the evaporation tank (5). In the evaporation tank (5), moisture equivalent to the steam mixed in the injection nozzle (2) is removed, and the sterilized liquid food is transferred to the discharge pump (1).
1), the food is transferred to a homogenizer (12) for homogenization, cooled to a predetermined temperature in a cooling section (13), and transferred to a storage tank C as a heat-sterilized food 8 storage section through a switching valve (14). .

The level of the evaporation tank (5) is controlled by the level controller (1).
0), the rotation speed of the rotor (1a) of the feed pump (1) is controlled to a predetermined level. Further, the sterilization temperature is maintained at a predetermined temperature by controlling the opening degree of the steam control valve (3) by a temperature controller (7).

A thermometer installed at the outlet of the holding tube (9) and a holding tube (9)
) The temperature and flow rate after steam mixing are measured by the flow meter (50) installed in Based on these signals, the plant controller (8) operates the switching valve (14). If the sterilization is good (that is, if the measured flow rate is below the set flow rate and the measured temperature is above the set temperature), the liquid transferred from the cooling section (13) A switching valve (14
) is activated, and if sterilization is poor, the switching valve (14) is activated to transfer the liquid food transferred from the cooling section (13) in the direction of B shown in FIG.

In the embodiment described above, it is also possible to further arrange a flow meter in the conduit connecting the feed pump (1) and the injection nozzle (2). By installing this flow meter, the flow rate before steam is mixed can be measured, and the holding tube (9
) can be adjusted. Incomplete condensation of steam occurs due to lack of pressure inside the holding tube (9).
When the value measured by the flow meter (50) disposed in The pressure can be adjusted.

The present inventor prototyped an example of the direct heat sterilization apparatus shown in FIG. 1, using the following commercially available products.

1: Feed pump (manufactured by Nakamura Metal Industry Co., Ltd.) 2; Injection nozzle (manufactured by Towa Techno Co., Ltd.) 3: Steam control valve (manufactured by Penn Co., Ltd.) 5: Evaporation tank (manufactured by Yasuda Iron Works Co., Ltd.) 7: Temperature controller (manufactured by Yokogawa Electric Corporation) ) 8 Nibrant controller (manufactured by Mitsubishi Electric) 9: Holding tube (manufactured by Towa Techno) 10 Nilevel controller (manufactured by Yokogawa Electric) 11: Discharge pump (manufactured by Yasuda Iron Works) 12: Homogenizer (manufactured by Mitsubishi Electric) (manufactured by Morinaga Engineering) 13: Cooling section (made by Morinaga Engineering) 14: Switching valve (made by Morinaga Engineering) 15: Back pressure adjustment valve (Morinaga Engineering) (YM204) By the way, the relationship between the flow rates before and after blowing steam into liquid food is expressed by the following equation (1).

Y=X umbrella pHH2-Hl)/ρ3 (H2-83>--
(1) In equation (1), Y is the flow rate of the liquid food after steam injection, X is the flow rate of the liquid food before steam injection, ρ1
is the density of the liquid food before steam injection, ρ3 is the density of the liquid food after steam injection, Hl is the enthalpy of the liquid food before steam injection, Hl is the enthalpy of the steam to be blown,
H3 indicates the enthalpy of the liquid food after steam injection.

In this embodiment, the density of the liquid food to be sterilized, the time for holding it at the heat sterilization temperature (i.e., the time for the liquid food to pass through the holding tube (9)), the liquid level in the evaporation tank (5), etc. are determined in advance. Once set, the holding tube (9) is
The length and cross-sectional area of is determined, which will be explained next.

Now, for example, the flow rate of the homogenizer (12) is set to 2150°C, the sterilization temperature is set to 153°C, and the allowable lower limit is set to 1.
Set the temperature to 47℃ and increase the liquid level in the evaporation tank (5) to 30%.
(capacity).

At this time, the density of milk is 1000 kg/m as the value of ρ1 in the equation (1) showing the relationship between the flow rates before and after the steam injection.
', the value of ρ3 is 950Kg/m', the value of Hl is the enthalpy of milk 74 Mcal/Kg, the value of H2 is 660 Xcal/Xg, the value of H3 is 1
40 Meal/Kg. Note that the above density and enthalpy values are estimated values from a literature (edited by the Dairy Technology Course Editorial Committee, Dairy Technology Course Volume 1 "Milk J, page 150, Breakfast Shoten, 1968).

In addition, the average discharge amount of the feed pump (1) during steady state is:
Since the flow rate of the homogenizer (12) is considered to be 21507 hours, the flow rate X of the liquid food before steam injection, that is, the value of X in the equation (1), is the same as the flow rate of the homogenizer (12). Assign the value X=2150 7 o'clock. In this case, from the above equation (1), the flow rate Y of the liquid food after steam injection is determined as shown in the following equation (2).

Y=lh 1/hour ---------- (2) In this case, the liquid food heated by being blown with steam by the injection nozzle (2) is heated in the holding tube (9). In order to pass through in 2 seconds, the cross-sectional area and length of the holding tube (9) are determined as follows. That is, if the cross-sectional area of the holding tube (9) in that case is s (cm2) and the length is d (cm), in order for the liquid food to pass through this holding tube (9) in 2 seconds, After said steam blowing? lii-shaped food will flow at sd/2 (cm') per second. Therefore, the following equation (3) holds true.

(sd/2)X3600=2550xlOOOOThis formula (
In 3), for example, if 5=10c■2, then d=
142cm=1.42m.

However, fluctuations occur in the flow rate Y in the holding tube (9). Therefore, when the dimensions of the holding tube (9) are set as described above, if the flow rate Y in the holding tube (9) fluctuates and the flow rate increases, the liquid food (pre-dispensing) in the holding tube (9) will increase. The flow rate of the liquid food (including steam) increases, and the time required for the liquid food to pass through the holding tube (9) becomes less than 2 seconds.

Therefore, when setting the dimensions of the holding tube (9), consider a margin of about 10% for the flow rate in the holding tube (9), and when the flow rate of liquid food in the holding tube (9) is 2800 7 o'clock. Also,
The length d and flow path cross-sectional area S of the holding tube (1) are set so that the liquid food passes through the holding tube (1) in 2 seconds. In this case, s and d are determined by the following equation (4).

(sd/2)X3600=2800X1000This formula (
4), the flow path cross-sectional area S of the holding tube (9) is calculated using the following formula (5
).

9=10c garden” −−−−−−−−−−−−−
-(5) When set as in the previous formula (5), the holding tube (9)
The length d is determined by the following equation (6).

d=1.56m --------- (6) Therefore, in this example, the feed pump (1)
Assuming that the discharge amount X in the steady state is 21507 hours, the dimensions of the holding tube (9) are set as shown in equations (5) and (6) above. In this case, if the flow rate Y measured by the front flow rate needle (50) is 2800.7 hours or less, the liquid food has passed through the holding tube (9) for more than 2 seconds, and the desired heating is achieved. Sterilization will take place.

However, if the predistribution amount Y exceeds 28007 hours, the transit time of the liquid food product in the holding tube (9) will be less than 2 seconds.

Therefore, in this embodiment, the switching valve (14)
When the measured value of the flow meter (50) is 28,007 hours or less, the liquid food from the cooling section 13 is transferred to the storage tank C.
and when the measured value is 2800, the liquid food is switched to be discharged to another location B.

Next, a test example conducted to examine the performance of the above embodiment will be explained.

The results of this test are shown in FIGS. 2 and 3.

By changing the set value of the liquid level controller 10 of the evaporation tank 5 in the steady state, the evaporation tank (5
Fig. 2 shows the variation in the flow rate in the holding tube when the liquid level of the liquid was suddenly changed from 30% to 40%.

In Fig. 2, the vertical axis shows the flow rate and the horizontal axis shows time. Fig. 3 shows the fluctuation of the sterilization temperature at this time, the vertical axis shows the sterilization temperature, and the horizontal axis shows the time. are shown respectively.

By changing the liquid level in the evaporation tank (5) as described above, the flow rate in the holding tube (9) becomes 25% as shown in Figure 2.
The sterilization temperature increased from 607:00 to 28407:00, and the sterilization temperature decreased from about 153°C to 147.5°C, as shown in FIG. Since the flow rate in the holding tube (9) exceeded the 2800 7:00 required to maintain the set sterilization time of 2 seconds, it was determined that sterilization was insufficient, and the switching valve (14) was activated to control the flow of liquid food. The direction was changed to another location B shown in FIG.

This result proves that even if the sterilization temperature is maintained at the set value, there are cases where the sterilization time does not reach the predetermined value. And in such a case, the device of the invention worked as designed.

Next, a second embodiment of the direct heat sterilization apparatus of the present invention will be described.

This second embodiment is an example in which skim milk was sterilized, and the length of the holding tube (9) in the first embodiment shown in FIG. The only difference is the set value of the flow rate Y, etc., and the other configurations are the same as in the first embodiment.

In this second embodiment, the flow rate of the homogenizer (12) is 2
The sterilization temperature was set at 153°C, and the allowable lower limit was set at 147°C. Further, the liquid level in the evaporation tank (5) was set to 30% (volume).

In this case, the relational expression (1
), density of skim milk is 1010Kg/m as ρ1, 960Kg/m3 as ρ3, enthalpy of skim milk 7'8 Kcal/kg as Hl, 660Kc as H2.
&1/Kg and 150 Kcal/Kg as H3, and further, as in the first embodiment, X=
2150 Substituting 7 o'clock and finding Y, Y is the following formula %
Formula % However, the flow rate Y in the holding tube (9) varies. When setting the dimensions of the holding tube (9), allow approximately 10% margin for the flow rate in the holding tube (9), and even when the flow rate of liquid food in the holding tube (9) is 28407 hours, The length d and flow path cross-sectional area S of the holding tube (1) are set so that the liquid food passes through the holding tube (1) in 2 seconds.

In this case, s and d are determined by the following equation (8).

(sd/2)x3600=2840xlOOOOThis formula (
8), the flow path cross-sectional area S of the holding tube (9) is calculated using the following formula (9
) Set as S = 9.62c Otori 2 −−−−−−−−−−−−−−−
(9) When the value of S is set as in equation (9), and if the cross section of the holding tube (9) is circular, its internal diameter is 35 mm. In this case, the length of the holding tube (9) is The length d is determined as shown in the following equation (10).

d = 1, 64 m −−1−−−−1−−−(
10) Therefore, in this example, X in the above formula (1)
The dimensions of the holding tube (9) are set as shown in the above equations <9) and (10), assuming that the value of is the average discharge amount of the feed pump (1) during steady state X=2150 7 o'clock.

In this case, if the flow rate Y measured by the flow meter (50) is less than 2840 7, the liquid food has passed through the holding tube (9) for more than 2 seconds, and the desired heat sterilization is achieved. will be held. However, if the flow rate Y exceeds 28407 hours, the transit time of the liquid food product in the holding tube (9) will be less than 2 seconds.

Therefore, in this embodiment, the switching valve (14)
When the measured value of the flow meter (50) is 28407 hours or less, the liquid food from the cooling section (13) is discharged into the storage tank C, and when the measured value exceeds 2840 hours, the liquid food is discharged. can be switched to be discharged to another location B.

Next, a third embodiment of the direct heat sterilization apparatus of the present invention will be described.

This third embodiment differs from the length of the holding pipe (9) and the switching valve (9) in the first embodiment shown in FIG.
14) The only difference is the set value of the flow rate Y for operating the flow rate Y, etc., and the other configurations are the same as in the first embodiment.

This third example is an example in which the raw material liquid for powdered milk was sterilized, and the flow rate of the homogenizer (12) was 2150 7
The sterilization temperature is 135℃, and the lower limit of fraud is 129℃.
was set. Also, reduce the liquid level in the evaporation tank (5) to 30% (
capacity).

In the above relational expression (1) for the flow rate before and after steam injection, ρl
The density of the raw material liquid for formula milk powder is 1040Kg/m3, ρ
3 is 990Kg/m', Hl is the enthalpy of raw material liquid for formula milk powder 72 Kcal/kg, H2 and shite is 650 Meal/Kg, H3 is 122 Kca
l/)[g, respectively, and then X=2159
When Y is determined by substituting 7 o'clock, Y becomes as shown in the following equation (11).

Y=2470 7 o'clock ----------(11)
However, fluctuations occur in the flow rate Y in the holding tube (9). Therefore, when setting the dimensions of the holding tube (9), allow approximately 10% margin for the flow rate in the holding tube (9), and when the flow rate of liquid food in the holding tube (9) is 2720 7 o'clock. Also, the length d and flow path cross-sectional area S of the holding tube (1) are set so that the liquid food passes through the holding tube (1) for at least 2 seconds. In this case, s and d are determined by the following equation (12).

(sd/2>X3600=2720xlOOOOThis formula (
12), the flow path cross section [s of the holding tube (9) is expressed by the following formula (
13).

s = 9, 62 cm2−−−−−−−−−−−
(13) When setting as in equation (13), holding tube (9
) has a circular cross-sectional shape, its inner diameter is 35 mm. In this case, the length d of the holding tube (9) is determined by the following equation (14).

d = 1, 57 m −−1−−−−−1−−(
14) Therefore, in this embodiment, said holding tube (9)
The dimensions of C are set as shown in equations (13) and (14) above. In this case, if the flow rate Y measured by the flow I wound (50) is 27207 hours or less, the liquid food has passed through the holding tube (9) for more than 2 seconds, and the desired heat sterilization can be achieved. will be held. However, if the predistribution rate Y exceeds 2720/hour, this means that the transit time of the liquid food product in the holding tube (9) is less than 2 seconds.

Therefore, in this embodiment, the switching valve (14)
When the measured value of the flow meter (50) is 27207 hours or less, the liquid food from the cooling section (13) is discharged into the storage tank C, and when the measured value exceeds 2720 hours, the liquid food is discharged. can be switched to be discharged to another location B.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and may be modified within the scope of the gist of the present invention as described in the claims. It is possible to do so.

For example, the homogenizer (12) and the cooling section (13)
etc. can also be arranged downstream of the switching valve (14).

Effects of C0 invention The effects achieved by the present invention are as follows.

(1) By measuring the passage time of liquid food through a holding tube, liquid food can be sterilized more reliably, which is extremely effective in terms of public health.

(2) By inexpensively improving the existing device, it is possible to create a sterilization device with improved layer reliability.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of the first embodiment of the present invention, FIG. 2 is a diagram showing the flow rate over time in the holding tube, FIG. 3 is a diagram showing changes in temperature over time in the holding tube, and FIG. The figure is an explanatory diagram of a conventional example,
It is. Explanation of symbols 1. Feed pump, 2. Steam mixing device (injection nozzle) 3...-
Steam control valve, 5 Evaporation tank, 7 Temperature controller, 8 Plant controller, 9 High temperature holding channel (holding pipe), 10 Level controller, 11 Discharge pump, 12 Homogenizer, 13 ...Cooling section, 14...Switching valve, 15...Back pressure adjustment valve 50...Flow meter, 51...Signal wiring, Patent

Claims (3)

[Claims] (1) High-temperature steam is directly mixed into the liquid food flowing in the flow path to heat it to a predetermined sterilization temperature, and the heated liquid food is maintained at the predetermined sterilization temperature in a high-temperature holding stream. In the direct heat sterilization method of heating and sterilizing the food by passing it through the channel, the passage time of the liquid food in the high temperature holding channel is measured, and the liquid food whose passage time is longer than a predetermined time is transferred to the heat sterilized food storage section. A direct heat sterilization method characterized by discharging the (2) A steam mixing device that directly mixes steam into the liquid food and heats it to a predetermined sterilization temperature into the flow path of the liquid food transferred by a feed pump, and a liquid heated by the vapor mixing device. A high-temperature holding channel through which the liquid food passes through while being maintained at the predetermined sterilization temperature, and a discharge device discharging the liquid food that has passed through the high-temperature holding channel into the heat-sterilized food storage section are provided. In the direct heat sterilization device, a passage time measuring means is provided for measuring the passage time of the liquid food in the high temperature holding channel, and the discharge device is configured to measure the passage time of the liquid food in the high temperature holding channel for a predetermined time or more. 1. A direct heat sterilization device comprising a flow path switching valve for discharging liquid foods into the heat sterilized food storage section and discharging liquid foods whose passage time is less than a predetermined time to another location. (3) The direct heat sterilization apparatus according to claim 2, wherein the transit time measuring means is constituted by a flow rate detection means for detecting the flow rate of liquid in the high temperature holding channel.