Living things are always advancing towards a trajectory of death. We spring up, mature and then we die. Foods will eventually decay but there are ways to reduce their deterioration, allowing longer shelf life. Foods deteriorate due to two reasons, (1) food safety problems and (2) food quality problems. Food safety problems involve issues of food contamination with food hazards. There are three types of hazards, biological, chemical and physical. Biological hazards are organisms that infect food such as bacteria, viruses, yeast, mold and parasites. These organisms cause illness or unacceptable organoleptic (sensory) changes in the food, and in some cases both. Biological factors are controlled in processing by controlling common conditions that provides suitability for microorganism growth such as:

  1. Food availability  
  2. Acidity
  3. Temperature
  4. Time
  5. Oxygen
  6. Moisture

Chemical hazards are natural and man-made substances that may be present in the food at high concentrations resulting in food poisoning. Physical hazards are extraneous material that may fall into the food during harvesting and processing such as glass, metal and stones that may lead to cuts and other injury while eating. 

Food safety standards are set by regulatory bodies such as your local health department, and federal agencies like the FDA and USDA. Food companies may also set their own food safety standards as long as they are not lower that the standards set by the appropriate regulatory agency.

Food quality problems may include food safety issues but is much broader. The term “quality” is a loose term referring to the standards as determined by regulatory agencies, the manufacturer and the customer. Ultimately, once basic regulatory standards are met, the customer will determine what is “good quality” for him or her. In this lesson, I will address a few common questions that you may have regarding food quality problems that perhaps you’ve encountered. 

Why do breads go moldy?

Bread goes moldy due to the presence of mold in the environment where it is processed or stored. Mold spores can be easily carried by air. When they land on your bread they will grow as long as they have enough moisture and nutrients. To prevent mold growth, breads must be processed in a clean environment and must be cooled prior to packaging. Bagging and sealing too quickly while the bread is still losing moisture will cause “sweating” in the bag; providing a suitable environment for spores to grow. Storing your bread in a clean environment and resealing the bag after opening will reduce the risk of contamination. Most commercial breads on the market are made with mold inhibitors such as calcium and sodium propionate, sorbic acid and potassium sorbate, benzoates, acetic acid and prune juice. Hence bread molding is more of a problem when you make homemade bread. If you have to make bread at home and want to keep it for longer, it is best to freeze it.  

Why do breads get stale?

Breads go stale due to a process called retrogradation. In this process, amylose molecules in the starch bond to each other, forcing water out from between them. This leaves the firm and crumbly texture characteristic of staling. To reduce staling, food manufactures add dough conditioners such as emulsifiers to bind amylose and hence restrict their movement. At home, you can reduce staling rate by freezing your bread. Freezing stops amylose from moving about freely.   

What caused by bread to collapse?

Wheat gluten must be strong enough to maintain the structure of bread during proofing (fermentation) and baking. Hence, if your bread has collapsed in the center, it may be due to a lack in the capacity for the gluten to hold its structure. This could be due to making bread with less than adequate gluten proteins. Typically you need at least 11% protein to make a decent bread. Therefore, select bread flour to bake with and not cake flour since cake flour has much less protein (about 7%). Nevertheless, if your protein content is correct, but your dough is underdeveloped (not kneaded enough) it will not have enough gluten to hold up the bread. At the other extreme, if the dough is overdeveloped (too much kneading), the gluten will breakdown and will not be able to hold the gases that are made during proofing. Adding too much yeast or fermenting too long will cause so much gas to be produced, that the gluten can’t hold them, resulting in collapse. Hence when baking, make sure that your flour has enough gluten-forming proteins, you give the right amount of kneading, and you add the right amount of yeast and fermentation time. 

Why do oils go rancid?

Oils go rancid due to breakdown caused by reaction with water or oxygen. Breakdown by water is called hydrolytic rancidity. It occurs when water reacts with triglycerides, breaking them down into glycerol and fatty acids. This causes the development of off-odors and off-flavors. Hydrolytic rancidity occurs faster at higher temperatures and in the presence of acid. Breakdown by oxygen is called oxidative rancidity or auto-oxidation. It occurs when oxygen reacts with fatty acids; breaking them down to release rancid-smelling volatile products. Autooxidation is increased when:

  1. lipids have more unsaturated fatty acid 
  2. lipids are exposed to air 
  3. lipids are exposed to light 
  4. lipids are exposed to higher temperatures 
  5. lipids are present in a low water activity environment 
  6. Lipids are exposed to metals e.g. copper and iron  

The general rule to keep oils from getting rancid is to keep foods properly contained to prevent entry of oxygen, keep them cool, and out of sunlight

What causes fruits and vegetables to rot?

Fruits and vegetables are living breathing organisms. As you may hear me say, “when you pick an apple it is not dead”. Enzymatic activity continues; leading to maturation, ripening and eventual decay. During this process, plant tissue gets softer due to breakdown of pectin and other structural components. Enzymatic activity can be reduced by cooling quickly following harvest.   

Why does my vegetables get soggy when I freeze and thaw them at home? 

During freezing, ice crystals grow within and outside of plant cells. If the crystals become too large they can rupture the cells, resulting in leakage of water and sogginess after thawing. To prevent this, commercial manufacturers use rapid freezing methods such as blast freezing to cool frozen fruits. This rapid cooling prevents any large ice crystal growth that would normally cause cell damage. Domestic refrigerators freezes food slowly resulting in cell rupture and sogginess after thawing. Hence, if you don’t have a flash freezer (which is very expensive) it is best not to freeze your own fruits and vegetables (unless you don’t mind the soggy texture).

Why is my jam so runny? 

The setting of jams is affected by sugar concentration, acid concentration, and pectin content. The function of the pectin is to entrap all the jam components into a gel. A disadvantage of pectin however is that it has a negative charge at pH >3.5. This causes them to push away from each other. Adding acid neutralizes this pH, preventing repulsion. The function of the sugar is to trap water and hence cause the pectin to be pulled closer to each other, trapping everything in its path into a meshy gel. Hence, a loose gel could be because:

  1. pectin content is too low
  2. pH is too high (not enough acid)
  3. too much water was added
  4. sugar content is too low, causing the gel matrix to be too watery
  5. the jam was not cooked long enough to boil out excess water 
  6. you agitated (shaked) the jam before it set

Hence the key to making a good jam is to follow the recipe

Courtney Simons
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.
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