Bottling was introduced following experiments by Nicholas Appert during the early 19the century in France. He took stout, wide-mouthed jars and filled these with meats, soups, fruits and vegetables. These filled jars were sealed with cork made from several layers of cross-grained corks and a paste, before being wired down like champagne corks. The jars were then heated in a water bath to cook them. Appert worked out the different cooking times for various types of foods. Nicoholas Appert published his ideas in 1810 in L'Art de conserver. His work was borrowed by Bryan Donkin in the UK for bottling fruit, which Donkin then developed into canning.
The key things are to ensure that you get the right bottles and stoppers for the job, and that they are all clean. Bottles must be scrupulously clean inside and any stubborn deposits must be removed using sand and water and a bottle brush. After cleaning, the bottles should then be rinsed and dried by stacking neck down to drain and dry. Bottles should be filled almost to the top, leaving 2 cm (¾ in.) between surface cork. For stoppers, fresh cork is best and old ones should not be used. Plastic stoppers can be used, but may pop out.
Preserving Food in Jars
Preserving food in jars is effectively the same as canning. It depends on complete sterilization by heat and then hermetically sealing the food sterilized. Bottling is commercially more costly than canning, but is a better for home cooks, because it requires little equipment and the bottles can be reused.
As a method, it is relatively modern, being hardly mentioned in cookbooks even by the early 20the century. Bottling really started with the work of Nicholas Appert (1749 - 1841) who patented a method for preserving foods in cans or jars. This was improved further by Chevalier Appert, who added heating in a water bath under pressure to the existing technique (an early form of autoclave). But it was the pioneering work of Louis Pasteur in 1854 and his work on fermentation that proved the causal link between microorganisms and spoilage. After this, theoretical progress was rapid. General acceptance only came about, though, when suitable jars with reliable seals were developed at reasonable prices.
Packing Foods into Bottles
Packing can be done via the Hot Pack or Cold Pack methods:
- Hot Pack: is the older method. The foods are cooked first, then put into heated sterilized jars and then sealed immediately. The jars may sometimes need heat treatment after that. However, the hot pack method can change the form and texture of the food.
- Cold Pack: is generally preferred today, although for foods where the texture is less important - purées or sauces - then hot pack remains preferable. In the cold-pack method, the fruit or vegetables are arranged in the jar raw (or part cooked), then cooked and sterilized in one operation in the sealed jar. In practice, jars with a screw ring must be screwed tight and then loosened a half turn to allow any pressure to escape rather than build up. The caps are then tightened again after being taken out of the sterilizing bath.
Liquids in Bottling
Fruits are usually packed in syrup. As a general rule, a strong syrup helps keep the taste, colour and texture of the fruit better. For commercial products, the best grades are packed in 40 - 60% syrups, with cheaper grades in as low as 10% syrups. A few fruits that are best enjoyed sour can be packed in plain water. Sugar syrups are prepared as a proportion of sugar to water; 10% is either 4 oz of sugar in 3½ cups or 100g of sugar in 1 litre of water. A hydrometer is useful if you will be doing a lot of bottling.
Vegetables are usually packed in a light brine (2% is a common concentration), but some are packed in water. A home method is to add 1 teaspoon of salt to 1 litre (1 quart) jar before filling with water.
Preparation for Bottling
Fruits and vegetables for bottling should be in good condition - fresh, undamaged and unbruised. The fruit and vegetables must be cleaned, destalked, peeled, cut into pieces, pitted, blanched, parboiled or otherwise prepared. A stainless steel knife is best for preparing fruit and vegetables for bottling. If the fruit tends to discolour when cut, they should be placed in an antioxidant solution - lemon juice or a mild salt and vinegar solution (30 g salt and 30 ml vinegar for 4 litres of water) until ready to put into the bottles. Peaches and tomatoes can be peeled easily after dunking them in boiling water.
Sterilization Temperatures for Bottling
The heat and action of boiling water will rapidly kill all organisms, including the heat-resistant spores of Clostridium botulinum (the cause of botulism), if the food is sufficiently acidic. This is the case for most fruit and tomatoes; sour fruit juices (i.e. acidic ones) can be sterilized just through pasteurization at 50 - 60oC (120 - 150oF) which is used for most cartonned fruit juices on supermarket shelves.
However, vegetables are usually slightly alkaline, so cannot be sterilized by boiling unless an acid (lemon juice or vinegar) is first added. To sterilize them without an acid, a higher temperature than boiling is needed, so vegetables are sterilized in an autoclave or pressure cooker - the pressure usually used in 0.7 kg/cm2 (10 ln/in.2) which requires a temperature of 115oC (240oF) at sea level. Some vegetables, e.g. spinach and Swiss chard, are sterilized at 1.05 kg/cm2 (15 ln/in.2) which requires a temperature of 122oC (250oF), because it takes too long at the lower pressure.
Sterilization Times for Bottling
The purposes of heating is to increase the temperature in the centre of the jar to the point that if it is held at that temperature for long enough, all organism will be killed. In the cold pack method, the food has to be cooked, as well. Since you cannot stick a thermometer into the centre of the sealed jar, we rely on the timings calculated by food scientists:
- For most cold-packed fruits, 30 minutes of processing submerged in a boiling water bath for 1 kg (1 quart) jars, where ½ kg (1 pint) jars take 25 minutes.
- Vegetables are trickier and must be cooked in a pressure cooker. Home bottling of vegetables is risky unless you follow the directions exactly and your jars are in good conditions with new rings. Cutting corners is dangerous.
Testing and Storage
When bottles are heated, the contents expand a little and some air is driven out. On cooling, a partial vacuum results as the contents contracts and the lid is sucked on tightly. In this situation, no organisms can enter. Jars should be tested, because if the seal is not perfect, microorganisms can get in and spoilage will result.
The best place to store bottled fruit is in a dark, dry place - light can bleach the colours of the fruits.
- Stobart, T. (1981) The Cook's Encyclopedia: ingredients & processes, Harper & Row. ISBN 0060141271.