How to make homemade preserves in glass jars

Step-by-step guide

Making preserves at home is a deeply rooted tradition in Andalusia. During times of abundant harvests — tomatoes from Almería, figs from Extremadura, peppers from La Vera, olives from Jaén — turning the surplus into preserves is a practical, economical, and delicious way to make the most of each season.

 

But for homemade preserves to be safe and last for months without refrigeration, the correct process must be followed. In this guide, we explain everything you need: from choosing the right jar to the pasteurization step, which ensures your preserves are free of bacteria and can last up to a year.

What do you need to make preserves in glass jars?

• Glass jars with twist-off lids or airtight seals (Weck, Le Parfait)
• New lids in perfect condition (never reuse twist-off lids that have already sealed)
• A large pot with a lid for the hot water bath
• Tongs or cloths to handle hot jars
• Wide-mouth funnel (optional but very useful)
• Your prepared or cooked ingredients

Buy Le Parfait jars

Step 1: Sterilize the jars before using them

Although new jars come clean, it is essential to sterilize them before adding the preserve. This removes any bacteria or yeast that could contaminate the product.

Pot method: place the jars (without lids) in a pot with cold water. Bring to a boil and keep at high heat for 10 minutes. Remove the jars carefully and let them dry upside down on a clean cloth.

Oven method: place clean jars in the oven at 120°C for 15 minutes. Lids should not go in the oven; sterilize them separately in boiling water for 5 minutes.

Important: always work with hot jars when filling them. A sudden change in temperature could break the glass.

Step 2: Prepare and fill the preserve

Once your product is ready (jam, fried tomato sauce, escalivada, honey, peppers, etc.), fill the jars leaving a headspace of 1 to 2 cm at the top, known as “headspace”. This space is necessary to create the vacuum during pasteurization.

Clean the top edge of the jar with a damp cloth before closing to ensure the lid seals properly. Close the lid firmly but without overtightening.

Step 3: Pasteurization- the most important step

Pasteurization is the process by which we apply enough heat to destroy pathogenic microorganisms, including the bacterium Clostridium botulinum, responsible for botulism. It is essential in low-acid preserves such as tomatoes, beans, asparagus, or meats.

Water bath: place the closed jars in the large pot, cover them completely with water and bring to a boil. For high-acid preserves (jams, pickles), 15–20 minutes is enough. For low-acid preserves (vegetables, fish), a pressure cooker or autoclave is recommended to reach temperatures above 115°C.

When removing the jars from the water and letting them cool, you will hear the characteristic “click” that indicates the lid has curved inward: this means the vacuum has formed correctly and the preserve is sealed.

Step 4: Check the seal and store properly

Once the jars are cool, press the center of the lid with your finger. If it moves down and pops back up (“clicks”), the vacuum has not formed properly and that jar should be consumed within the next few days and kept refrigerated.

Properly sealed preserves can be stored in a cool, dark, and dry place (a pantry, cupboard, or cellar) for 6 to 12 months. Once opened, consume within 3 to 7 days and always keep refrigerated.

Recommended jars for homemade preserves

  • Twist-off jars: the most popular for jams, preserves, sauces, and fruit preserves. The metal lid with twist system creates a very effective vacuum. Available in sizes from 212 ml to 1,000 ml.
  • Weck jars: closure system with rubber seal and metal clips. They are sterilizable, reusable, and highly valued for their aesthetics. Ideal for premium preserves or gifting.
  • Le Parfait jars: lever-lock closure with airtight rubber seal. Very traditional in France and southern Spain. Excellent for vegetable preserves and whole fruits in syrup.

At The Pack Stock you will find all these formats in packs from small quantities. No high minimum order, with express shipping to Andalusia and all of Spain.

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