Becoming more important especially in localities where winter temperatures drop below freezing, the average relative humidity in heated rooms ranges from 10 to 20% in winter. This is drier than deserts; optimal humidity should be between 40-50%. Table LXXVI provides weights of air, water vapor, and their mixtures at various temperatures under normal atmospheric pressure (29.921 inches of mercury). The relation of air temperature to wet and dry bulb thermometer readings affects relative humidity as shown in Fig. 208.
The National Association of Ice Industries advises on placing food and using ice properly:
- Place delicate foods requiring low temperatures directly under the ice chamber for fresh, cold air.
- Milk needs special care due to bacterial growth; place it in sterilized containers where it won't freeze (below 28°F).
- Butter should be tightly sealed as it absorbs odors easily and tends to prevent rancidity at lower temperatures.
- Desserts like jellies, charlottes, and heavy cream desserts go in the coldest compartment until set.
- Meats should be placed on a clean dish on the bottom of the food compartment; cooked meats dry out quickly so use tightly covered containers.
- Fish may be kept safely if placed in a tightly covered vessel.
- Leftovers with cream sauces or custards should go in the coldest location possible, while others can go in meat compartments.
- Berries and cherries are especially prone to mold; place them on shelves above meat compartments for dry cold air circulation.
- Eggs do not need the coldest place but will keep well on middle shelves.
- Vegetables and fruits should be washed, then placed in tightly covered jars or containers with minimal crowding.
For overhead ice refrigerators:
- Cold air drops from the ice chamber to the food compartment; warm air rises along side walls back to the ice chamber.
- Place milk, butter, broths, and other delicate products on middle portions of top shelves; meats, fish, and desserts should be placed on middle shelves just below.
Ice usage tips:
- Use ice year-round for consistent food preservation regardless of temperature.
- A well-filled ice chamber maintains proper refrigeration with less frequent ice replenishment.
Key Takeaways
- Maintain optimal humidity levels (40-50%) for health and comfort in heated rooms.
- Place delicate foods like milk, butter, and broths directly under the ice chamber for best preservation.
- Use tightly sealed containers to prevent bacterial growth and odor absorption.
Practical Tips
- Regularly check humidity levels with a hygrometer to ensure optimal conditions inside your refrigerator.
- Keep air ducts open in refrigerators to allow proper circulation of cold air.
- Sterilize containers before storing perishable foods like milk and meat broths.
Warnings & Risks
- Avoid placing food directly on shelves without containers as this can lead to bacterial growth and contamination.
- Do not let ice levels drop too low in the refrigerator, as it will cause faster melting and reduced efficiency.
Modern Application
While modern refrigeration technology has advanced significantly since 1927, understanding historical methods of food preservation remains valuable. Proper humidity control, strategic placement of foods based on temperature sensitivity, and maintaining cleanliness are principles that still apply today for optimal food storage.
Frequently Asked Questions
Q: What is the ideal relative humidity range in heated rooms during winter?
The text advises keeping the relative humidity between 40-50% to ensure good conditions regarding health and comfort.
Q: Why should milk be placed in a sterilized container?
Milk is an ideal medium for bacterial growth at favorable temperatures, so placing it in a sterilized container helps prevent contamination and ensures its quality.
Q: What are the benefits of keeping vegetables and fruits in tightly covered jars or containers?
Vegetables and fruits stored in tightly covered containers stay fresh longer due to reduced exposure to air, which can cause them to dry out quickly. This also helps prevent contamination from bacteria.