Pressure and Temperature in a Home Autoclave

A home autoclave helps homemakers greatly simplify the canning process and save time. The cooking process occurs under pressure higher than atmospheric and at temperatures above 100°C. This is necessary to sterilize the canned goods from pathogenic microorganisms, ensuring product safety and extending shelf life.

During sterilization in the autoclave, high pressure is created, and since the device is tightly sealed, neither liquid nor air can escape.

To eliminate all harmful bacteria, the product needs to be boiled at a temperature of at least 100°C for a minimum of 20 minutes. Some types of pathogenic organisms, including botulism toxin, can survive under such conditions. The autoclave allows the use of higher temperatures, at which all bacteria are killed.

The drawback of this method is that canned goods can burn in the autoclave if left for too long. Always follow the recipe and maintain the temperature and pressure that will kill bacteria but keep the products in a normal and edible state. The pressure at which to cook in an autoclave depends on the type of product and the required temperature. For example, vegetables should not be cooked at temperatures higher than 100°C, while meat should not be processed at less than 110°C. Temperature norms for preparing different products can be found in the cookbook that comes with the autoclave.

If the temperature in the autoclave is increased, the pressure will also rise. These parameters are interconnected. To properly cook products, you need to understand what pressure should be in the autoclave. Accurately determining the relationship between temperature and pressure is impossible because other factors influence the indicators. We offer an introductory table showing the dependence of temperature on the absolute value of pressure.

P (atm)	T (°C)
1	6.7
1.3	45
2	80
3	100
3.5	110
4.5	120
5.5	126
6	132
8	142

The pressure gauge in the autoclave shows the relative value of pressure. At 110°C, it reads 3.5 atm; at 120°C, it shows 4.5 atm. The pressure depends on the speed and temperature of the heating, as well as the volume of air inside, between the lid and the jars. In the table, a value of two atm corresponds to a gauge reading of 1 atm, which can cause confusion.

The air inside the autoclave heats up and expands much faster. At 110°C, the pressure inside the device exceeds 3 atm. We recommend not focusing on the pressure readings. It is more effective to monitor the thermometer. As soon as the autoclave heats up to 110°C, reduce the heat.

It's also important to consider the cooking time for each canned product, as it differs depending on the type of product.

Meat – more than 30 minutes;
Poultry – 27 minutes;
Fish – 20 minutes;
Mushrooms – 15 minutes;
Vegetables – 10 minutes;
Fruits – up to 8 minutes.

The cooking time should start from the moment the autoclave reaches its working mode. To preserve the taste and nutrients in the canned goods, you should cook in the autoclave at temperatures up to 120°C, ideally between 105-115°C, to ensure the products remain safe.

Important! The size of the jars does not affect the temperature and pressure; they remain the same. However, with larger volumes, the cooking time may increase by 5-15 minutes.

It is essential to determine the necessary pressure and temperature to destroy microorganisms inside the cans. Only an autoclave can guarantee the safety of canned products.

If you're not sure about the quality of the meat, it's better not to preserve it. Some strains of botulism can survive even in extreme conditions.

To be certain of the pressure to pump into the autoclave, it is necessary to follow the pressure table and heating temperature. For meat and fish preserves, it should be over 105°C.

Modern autoclave models require almost no human intervention. You only need to pump the pressure and set the required temperature. When the device heats up, a system will activate that prevents the temperature from rising further.

Preserves typically last from 2 to 5 years. If it's fish, it is not recommended to store it for more than two years. Vegetables can last about three years, while meat preserves can last up to 5 years.

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