There are 3 conditions that you can have coffee beans in: unroasted, roasted, and ground. Each of these has a different recommended storage life.
The primary reason that coffee ages is air volatilizes the oils that give it the flavor, aroma, and body. To volatilize is to cause a substance to disperse into vapor. So over time coffee loses flavor, aroma, and body.
Unroasted coffee beans are straight from the milling process. They are pale green to light tan in color. They may be called green coffee beans. They may also be called dry coffee beans, as they have only about 10% water weight left.
Unroasted coffee has the longest shelf life. You can store it for a few years! Any oils are deep inside the bean.
Coffee usually reaches customers already roasted. Only the most intense coffee advocates are interested in roasting their own coffee beans. So this condition is the most common.
The roasting process converts the coffee beans' acids into oils, and the heat slowly pushes the oils to the surface. These elevated surface oils are slowly volatilized into air, so roasted coffee has a shorter shelf life than unroasted coffee.
You can store roasted coffee beans for 2-4 weeks. The longer number is under optimal storage conditions.
Light roast coffee may have a slightly longer shelf life than dark roast. Light roasts contain more acids, less oils, and the oils are deeper in the bean. Dark roasts contain less acids, more oils, and the oils are closer to the surface.
Coffee can also be purchased roasted and ground. This saves time for customers.
Grinding coffee cuts/tears beans into small pieces, so all the oils are close to the surface during the extraction process. But that means they're vulnerable for storage, too. The oils are quickly volatilized into air, so ground coffee has the shortest shelf life. You can store ground coffee beans for only 2-10 days. The longer number is under optimal storage conditions.
The optimal conditions for storing coffee are darkness, low humidity, room temperature, and in a vacuum. These ensure it stays fresh for brewing.
Light is a form of energy. Adding energy to coffee will age it and breakdown molecular bonds in flavor and aroma compounds.
The water molecules in humid air will slowly dissolve some of the coffee beans' flavor and aroma.
High temperatures are a form of energy. Adding energy to coffee will age it and breakdown molecular bonds in flavor and aroma compounds.
Low temperatures (such as in refrigerators and freezers) cause an increase in air relative humidity and condensation. The water molecules will slowly dissolve some of the coffee beans' flavor and aroma.
Keeping coffee away from oxygen and potential humidity reduces aging. Many bags have one-way valves that allow customers to squeeze most of the air out. There are coffee storage containers available that have valves or pumps to remove air.
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