Every piece of food, whether fruit, vegetables or meat, no matter how fresh, is filled with tiny, invisible organisms which cause it to spoil. The air, no matter how clear it may look, is filled with these tiny organisms which spoil food. These organisms are of two classes: yeast spores, which attack fruits, and bacteria, which attack vegetables and meats.

Yeasts are killed by lower degrees of heat than bacteria; 170° to 180° Fahrenheit will usually be sufficient. A short boiling is therefore enough for killing yeast in fruits. Bacteria, however, resist destruction by heat for a long time. Two and even more hours at boiling point (212° F.) are required to render all fish, meats and most vegetables, proof against spoiling.

This is the reason fruits may be cooked in an open kettle, poured into jars hot, capped and clamped at once, before the temperature falls much below the boiling point. Vegetables and meat handled this way will give bacteria a chance to light on food while being poured into the jar, and will cause it to spoil.

All vegetables and meats should be cooked in closed jars and not exposed to the air. When the food in jar is hot it is very much expanded; in cooling, it shrinks, forming a vacuum.

In shrinking it draws the cap down tight, and by the atmospheric pressure of about 15 pounds to the square inch, holds it tighter, until when cold the cap is held tight and securely.

Jars should be sterilized by placing in cold water and letting the water come to boiling point. Caps and rubbers should be dipped in boiling water, but not allowed to remain there.

Jellies, Preserves And Canning Of Foods

Preserving, in the ordinary sense, means the cooking of fruits in thick syrup made of equal weights of sugar and fruit, little or no water being used, according to the fruit.

Canning is preserving sterilized foods in sterilized air-tight cans or jars. Meats, fish, vegetables and fruits are thus preserved.

General Directions For Filling Jars

Remove the jars from the boiling water. Place fruit in jar, the rounded side of fruit towards the outside of jar. Fill with syrup. Use blade of silver knife to push fruit away from jar to allow air bubbles to rise to the surface and break. Fill to overflowing; place the rubber on the jar, put on the cover and screw it tight. Turn the jar upside down to see if it is airtight.