CHAPTER XII. PRESERVATION OF FOODS IN THE HOME Influence of Temperature on Bacteria in Foods. — Temperature has an important influence on the growth of bacteria. Most bacteria, yeasts, molds, and related organisms grow best at a temperature between 68° and 122° F., and do not grow at a temperature below 45° to 55° F. Cold retards their growth and tends to preserve these microorganisms as well as the food unchanged.
<Callout type="important" title="Important">Foods removed from cold storage are inferior in keeping qualities to the corresponding fresh foods.</Callout> Freezing decreases the number of bacteria but does not immediately kill them. Most molds are easily destroyed by freezing. Bacteria will multiply in milk as long as it is not frozen entirely solid. Milk of good quality will stay sweet and in perfect condition for more than a week if it is held at a temperature slightly above the freezing point.
Effect of Refrigeration Upon Foods. — Cold does not destroy the microbes in food but retards their activity and growth. The decomposition of foods is caused by the action of their own enzymes and more frequently by the activity of bacteria, yeast, and molds. Fruits and vegetables should be stored at a temperature slightly above 32° F. and in a humidity at about 60 per cent of saturation, in order to diminish evaporation without developing molds.
Ice and Its Relation to Food. — Ice checks the growth of living things to the extent that it almost causes the smallest forms of vegetable and animal creation to cease to exist as life. Usually, it does not kill but produces a condition of latent life, like the winter sleep of bears, beavers, snakes, and other creatures.
Care of Milk in the Home. — Farmers' Bulletin No. 1207 of the United States Department of Agriculture gives the following dissertation on the care of milk in the home: No matter how well milk has been handled up to the time it is delivered to the consumer, it cannot be expected to keep well if it is then carelessly treated.
<Callout type="warning" title="Warning">Milk should be kept clean, covered, and cool; otherwise, bacteria can multiply rapidly.</Callout> In towns and cities, the best way of buying milk is in bottles. In this form it can be kept clean and cool more easily during delivery and is much more convenient to handle.
The Application of Refrigeration to Milk. — The following data on the application of refrigeration for cooling and storing milk is taken from United States Department of Agriculture Bulletin No. 98: Effect of Freezing on Milk. — While the action of cold on milk at a temperature above the freezing point has no other effect than that of varying the density and viscosity, it changes the chemical and physical composition.
<Callout type="risk" title="Risk">Milk frozen for several days may develop hard-to-dissolve clots due to bacterial growth.</Callout> If the milk is held at 32° F., for a few days, some types of bacteria may grow and multiply slowly. With a good quality of milk, i.e., that containing few bacteria, it may take weeks or even months for them to gain great headway.
Influence of Temperature on the Bacteriological Flora of Milk. — Each species of bacterium found in milk and each particular variety has an upper and lower temperature limit beyond which it does not grow, and a certain temperature, called the optimum, at which it grows best.
<Callout type="tip" title="Tip">Keep milk covered to exclude dirt and bacteria.</Callout> It should be kept away from foods of strong odor, such as onions, cabbage, or fish. Bottled milk should be kept in the bottles in which it is delivered until needed for use.
Influence of Time on the Bacteriological Flora of Milk. — The influence of temperature and time bear certain definite relations to each other; hence, a study of one necessarily includes a study of the other. Table XCIV serves to illustrate the effect of time as it relates to bacterial growth in milk.
Key Takeaways
- Cold temperatures slow down bacterial growth and preserve food quality.
- Milk should be stored at slightly above freezing temperature for best results.
- Proper handling of milk is crucial to prevent bacterial contamination.
Practical Tips
- Store milk in sealed bottles or containers to minimize exposure to bacteria and odors.
- Keep fruits and vegetables in a cool, humid environment to slow down decomposition.
- Regularly clean and sanitize refrigerators and other storage areas to maintain hygiene.
Warnings & Risks
- Improper handling of milk can lead to rapid bacterial growth even at low temperatures.
- Using unclean containers or surfaces for storing food can introduce harmful bacteria.
- Exposure to strong odors can affect the taste and quality of stored foods.
Modern Application
While many of the techniques described in this chapter are still applicable today, modern refrigeration technology offers more precise temperature control and better preservation methods. Understanding these principles remains crucial for effective food storage during emergencies or when traditional refrigeration is unavailable.
Frequently Asked Questions
Q: How does freezing milk affect its quality?
Risk
Freezing milk can cause the formation of hard-to-dissolve clots due to bacterial growth, making it less suitable for consumption.
Q: What are the best storage conditions for fruits and vegetables?
Tip
Store fruits and vegetables at a temperature slightly above 32°F (0°C) with a humidity of about 60% to minimize evaporation and prevent mold growth.
Q: Why is it important to keep milk covered?
Warning
Covering milk prevents the introduction of bacteria from the air, which can spoil the milk even if stored at a low temperature.