How do you preserve food properly in jars?

Autumn – this is precisely the time when part of the summer and autumn harvest is preserved in jars. Vegetables are pickled, jams and sauces are made, mushrooms and compotes are prepared, and meat is preserved. Proper preservation allows you to enjoy seasonal produce for much longer, but experts from the State Food and Veterinary Service (VMVT) remind us: a tightly sealed lid alone does not mean that the product is safe.

The essence of preserving is to create conditions in which microorganisms that spoil food or pose a danger to humans cannot multiply, and to protect the prepared product from recontamination. This can be achieved using acid, sugar, salt, cold, heat treatment or a combination of several of these factors. 

This is precisely why strawberry jam, pickled gherkins and tinned meat cannot be treated in the same way – different products require different preservation methods.

“When it comes to preserving food, the most important factor is the conditions created for microorganisms. For some products, acidity helps to keep them safe; for others, it is sugar, salt or heat treatment. Particular care must be taken with low-acidity products – meat, fish, mushrooms and some vegetables. If they are preserved incorrectly, conditions may arise that allow dangerous microorganisms to multiply; therefore, one should not improvise or rely solely on the usual method of boiling,” – says Indra Urbonavičiūtė, Senior Specialist at the Animal Products Division of the State Food and Veterinary Service (VMVT).

The greatest caution is required when preserving low-acidity products

Most fruits, berries and properly acidified products are more acidic, so this environment is not favourable for some harmful bacteria. The situation is different with low-acidity foods – meat, fish, most vegetables and mushrooms.

In such products, particularly when stored in airtight, oxygen-free conditions, improper preservation can create conditions favourable to Clostridium botulinum bacteria. Their spores are heat-resistant, so simply boiling them may not be sufficient. 

Improperly prepared home-made preserves are one of the well-known risks of foodborne botulism, therefore the State Food and Veterinary Service (VMVT) recommends following reliable recipes tailored to the specific product and the recommended preserving methods when preserving food.

A long shelf life does not necessarily mean that the product contains a lot of preservatives

Meat preserves require particular attention. Meat contains a high moisture content and has low acidity; therefore, reliable heat treatment is essential for tinned meat stored at room temperature for long periods. 

In industrial production, during sterilisation, not only are the temperature and heating time precisely controlled, but also the way in which heat is distributed throughout the entire container. It is important that sufficient heat reaches even the parts of the product that heat up most slowly. 

Modern technology allows this process to be controlled with ever-greater precision. Sensors and computerised systems help to monitor the temperature and assess how heat is distributed within the product. The aim is to ensure food safety, whilst at the same time not heating the product for longer than necessary, so that its flavour, texture and nutritional value are preserved as much as possible.

Therefore, the long shelf life of sterilised tinned meat does not in itself mean that they contain large amounts of preservatives. The safety and long shelf life of properly produced tinned foods are primarily ensured by a correctly selected heat treatment process and airtight packaging. If there are any doubts about the safety of home-made tinned food, it should not be tasted simply to ‘check’ it – botulinum toxin cannot be reliably identified by the product’s appearance, smell or taste.

Preserving is an age-old method of food preservation, but safe preserving is not a matter of guesswork. It doesn’t matter what goes into the jar – apples, vegetables, mushrooms or meat – the most important thing is to choose a suitable and safe preserving method for each product.