Preserves: essential guidelines for safe preparation

30 July 2024

Every year in Italy, there are between 20 and 30 cases of botulism, a severe food poisoning caused by the ingestion of Clostridium Botulinum bacteria. Almost always, the source is homemade or artisan preserves prepared without following basic hygiene measures.
Preserves are foods that, thanks to specific preparation techniques, can be stored for a long time without altering their taste, texture, and nutritional properties. Preservation occurs through processes that prevent the growth of bacteria and enzymes responsible for food spoilage. Among the most common methods are sterilisation, the use of sugar, salt, vinegar, and oil—ingredients that, thanks to their chemical properties, block or greatly slow microbial growth.
For several years, a detailed guide created by the Istituto Superiore di Sanità has been available. Below is a schematic summary of the main guidelines.

Hygiene and equipment

Personal and kitchen hygiene is the first crucial step in preparing preserves. Washing hands with soap and mechanical rubbing is essential to remove microorganisms from the skin.
Hands must be washed before handling food and every time you switch tasks. Wash hands whenever visibly dirty, after using the toilet, eating, smoking, coughing or sneezing, and after touching potential sources of contamination such as raw food, pets, or waste.
Utensils must be washed with appropriate detergents and rinsed thoroughly to remove any residue. The use of disinfectants like sodium hypochlorite diluted to 5-7% is recommended for effective sanitisation. Equipment must be carefully selected and kept clean. Pots used for water bath processing must be large, with the water level at least 5 cm above the jar lids. Tools like wide-neck funnels and plastic spatulas make filling and air removal easier. Cooking pots should be stainless steel, while food containers should be glass (note that clear glass allows light to pass through).

Selecting and treating the products

The quality of the ingredients is crucial. Choose seasonal fruits and vegetables, preferably local or organic, to reduce pesticide residues. Products should be processed within 6-12 hours of harvest to maintain their characteristics. Avoid overly ripe or unripe produce to ensure the right texture and taste. Use wine vinegar, preferably white, with an acetic acid content of no less than 5%. Oil should be high quality (preferably extra virgin olive oil), sugar should be granulated (or special jam sugar with added pectin), and salt should be sea salt.
Wash vegetables thoroughly under running water to remove dirt and residues. Soaking in water with baking soda can help reduce surface pesticides. After washing, dry the vegetables, remove damaged parts, and cut them as needed. Treat products prone to oxidation with lemon juice or by blanching.
Blanching means heating the vegetables in boiling water or steam for a short period. This process halts enzymatic activity, preserving the colour, taste, and texture of the vegetables. It’s important to follow specific timing for each type of vegetable to avoid damage. After blanching, vegetables must be quickly cooled in cold water or ice to stop the cooking process.

Containers: all the steps

Containers must be thoroughly sanitised before use to prevent contamination. This can be done by boiling the jars and lids in water for at least 10 minutes or using a high-temperature oven. Sanitisation eliminates microorganisms, preventing bacteria and mould growth that could compromise the preserves’ quality and safety. After sanitising, let the containers air-dry on a clean cloth without touching the inside of the jars or lids to maintain sterility. Note that sanitising is not the same as sterilising: sterilisation completely destroys all microbial forms, including spores, which are highly heat-resistant (at 100°C, this process may take several hours).
Filling the containers is a delicate operation. Use a clean funnel to pour the contents into the jars, leaving a headspace of about 1-2 cm to allow for expansion during heat processing. Do not overfill the jars to prevent overflow and ensure proper pasteurisation. After filling, remove any air bubbles with a plastic spatula, running it along the sides of the jar. Clean the rims with a damp cloth to ensure an airtight seal.
Pasteurisation is a crucial step
Water bath processing is the most common method: jars are immersed in boiling water for enough time to destroy pathogens.The duration and temperature vary depending on the type of product and jar size. For example, fruit preserves generally require a shorter processing time than vegetable preserves. Always follow specific guidelines for each product to ensure the process is effective.

Inspection and storage

Dopo la pastorizzazione, i barattoli devono essere ispezionati attentamente per verificare che i coperchi siano sigillati correttamente. Un coperchio sigillato correttamente non dovrebbe flettersi al centro quando premuto. Se il coperchio emette un suono di “click” al centro, significa che non è sigillato correttamente e il contenuto potrebbe essere compromesso. Conservare i barattoli in un luogo fresco e buio, lontano dalla luce diretta e dalle fonti di calore, per preservare la qualità delle conserve. È consigliabile etichettare ogni barattolo con la data di produzione e il tipo di conserva per tenere traccia della loro freschezza.
Dopo l’apertura, le conserve devono essere conservate in frigorifero e consumate entro un tempo variabile a seconda del tipo di prodotto. Conserve acide o acidificate e vegetali in salamoia possono durare fino a due mesi, mentre marmellate e passate di pomodoro devono essere consumate entro una settimana. Sughi, salse e succhi di frutta vanno consumati entro 4-5 giorni dall’apertura.

After pasteurisation, jars must be carefully checked to ensure the lids are properly sealed. A properly sealed lid should not flex when pressed in the centre. If the lid makes a clicking sound when pressed, it is not sealed correctly, and the contents may be compromised. Store jars in a cool, dark place, away from direct light and heat sources, to preserve quality. Label each jar with the production date and product type to monitor freshness.
Once opened, preserves must be stored in the refrigerator and consumed within a time frame that varies depending on the product. Acidic or pickled preserves can last up to two months, while jams and tomato sauces should be consumed within a week. Sauces, dressings, and fruit juices should be consumed within 4-5 days of opening.