Home Food Preservation

Nowadays, consumers have become more and more interested in being informed about their food. More specifically, they search for information on what their food contains, how it is produced, its carbon footprint, etc. At the same time, they are more aware of food risks and the fact that food safety may be compromised not only during the production stages but also during storage. There are several sources of information, but not all of them are scientifically valid (1). Many webinars are also available, like the University of Minnesota Extension one.

Food preservation is any of a number of methods by which food is kept from spoilage after harvest or slaughter. Food spoilage may be defined as any change that renders food unfit for human consumption. These changes may be caused by various factors, including contamination by microorganisms, infestation by insects, or degradation by endogenous enzymes (those present naturally in the food) (7). 

Food preservation can take place in several ways. Some of them include canning, freezing, drying, smoking, fermenting, and pickling (2). For each way of preservation, consumers must consider some specific possible risks.

Canning

The main risk in canned foods is the growth of the bacterium Clostridium botulinum, which may cause botulism. This bacteria can survive in soil and water for many years, either as spores or as vegetative cells. When the conditions are ideal, the spores will produce vegetative cells that may produce a deadly toxin in just 3-4 days. An ideal environment is a food of low acidity and high moisture content, a temperature between 40 °F and 120 °F (4,4 °C and 48,8 °C), and oxygen below 2% (4). 

The truth is that the majority of bacteria, yeasts, and molds cannot be removed easily from food surfaces. Washing can reduce their load only slightly, while peeling and blanching can make a significant difference. Generally, if the food has been appropriately sterilized, spoilage will not occur in storage temperatures below 95 °F (35 °C). Storage temperatures between 50 °F and 70 °F (10 °C and 21 °C) are considered to be ideal for quality retention (4).

Freezing

Freezing is a common way of food preservation; however, many of us need to learn how to freeze our food better, properly, and for how long. Also, we must mention that freezing cannot improve the quality of any food, but it can only help preserve the product’s initial quality. Some indicative months of storage at 0 °F (-18 °C) are (3):

• 8-12 months for fruits and vegetables,
• 6-9 months for poultry,
• 3-6 months for fish,
• 3-4 months for ground meat,
• 1-2 months for cured or processed meat.

For fruits and vegetables, the process of blanching (scalding vegetables in boiling water or steam for a short time) can stop enzymatic action, which otherwise would cause flavor, color, texture, and nutrient loss, even at 0 °F (-17 ºC).

0 °F (-17 ºC) or lower is considered the best temperature for freezing and storing food. It is always recommended to freeze foods directly after they are packed and sealed and not to overload the freezer with unfrozen food. This would increase the temperature of the frozen foods very quickly, which is undesirable. It is also suggested to leave space among new packages (with higher temperatures), so the cold air can circulate freely around them and freeze them more quickly.

Drying

The principal spoilage that can occur in dried foods is insect contamination and moisture reabsorption since this type of environment is not ideal for the growth of microorganisms. There are some things to remember when it comes to dry foods (5):

1. Cool the food completely; if not, it will sweat, and mold will find enough moisture content to grow.
2. Pack dried foods into clean, dry, and insect-proof containers as tightly as possible but without crushing them. Vacuum packaging is also a good option.
3. Pack foods in quantities that can be used all at once (consumption or recipe). Do not forget that each time a package is re-opened, the dried food gets exposed to air and moisture that can affect its quality and result in spoilage.
4. Sulfured fruit should not touch metal because sulfur will react with the metal and, as a result, cause color changes in the fruit. So, it is recommended to place the fruit in a plastic bag and then store it in a metal can. 
5. Cool, dry, and dark areas are considered the best places to store dried food. Generally, dried foods can be stored from 4 months to 1 year, depending on the storage temperature. As the temperature increases, the storage time decreases. More specifically, the majority of dried fruits can be stored for one year at 60 ºF (15 ºC), while, when the temperature is 80 ºF (27 ºC), storage time decreases to 6 months. Remember that vegetables have about half the shelf-life of fruits.
6. Glass containers are an excellent option for storage because any moisture that collects inside can be detected easily. Foods affected by moisture but not spoiled should be consumed immediately or redried and repackaged. In every case, moldy foods should be discarded.

Fermenting and pickling

In fermented and pickled foods, the acidity level is as essential to their safety as it is to their organoleptic characteristics. For this reason, never change vinegar, food, or water quantities in a recipe or use vinegar of unknown acidity. In any case, there must be a minimum and uniform level of acid throughout the whole product to make it difficult for botulinum bacteria to grow. The raw material is of great importance, so we have to use fresh and firm fruits and vegetables. At the same time, we must be very careful with the proportions because they will affect both flavor and food safety in many cases (6). 

References

1. https://reeis.usda.gov/web/crisprojectpages/0226960-national-center-for-home-food-processing-and-preservation.html
2. https://nchfp.uga.edu/#gsc.tab=0
3. https://nchfp.uga.edu/how/freeze/freezer_shelf_life.html
4. https://nchfp.uga.edu/how/general/ensuring_safe_canned_foods.html
5. https://nchfp.uga.edu/how/dry/pack_store.html
6. https://nchfp.uga.edu/how/can_06/prep_foods.html
7. https://www.britannica.com/topic/food-preservation