How long can coffee sit out?

In this brief guide, we will answer ‘how long can coffee sit out?’ Also, we will see what changes occur in coffee and also the factors that play a role in this.

How long can coffee sit out?

Brewed coffee can only last for 30 minutes before the flavor begins to degrade. Although it will still be safe to consume after longer periods and even after a day, coffee starts losing its properties right after being brewed. It will not only lose its pleasant fragrance but also may start tasting rancid and also an unpleasant bitter or sour taste may also develop.

However, plain black coffee lasts longer than coffee beverages containing milk and sugar. Hot coffees with milk added are only safe to drink for two hours at room temperature. This is because milk is highly perishable and favors the growth of microorganisms. When stored in the refrigerator, coffee drinks containing milk or other ingredients (sugar, cream) can be stored for 3 days in. However, there is an increase in the acidity and the microbial count of the beverage, in addition to the development of off-flavors related to the oxidation of lipids (6).

What happens when brewed coffee sits out for long?

When brewed coffee sits out for long, chemical reactions occur, especially due to the action of oxygen resulting in changes of the properties of the coffee drink, such as flavor, aroma and antioxidant activity. The complex aroma profile of coffee is formed by furans, pyrazines, thiols, aldehydes and many other volatiles. After brew, these volatile aromatic compounds are gradually lost due to physical diffusion/volatile loss and chemical degradation reactions, such as polymerization or oxidation (1). 

In addition, coffee is rich in polyphenols, antioxidant compounds, and therefore has beneficial health effects on the human body. The oxidation of polyphenols leads to the formation of H2O2, hydrogen peroxide, which could be toxic, and that increases with storage time of brewed coffee (2).

Factors responsible for coffee going stale

Following factors are responsible for the length of time brewed coffee remains safe to consume;

  • Temperature of brewing
  • Exposure to air
  • How do you keep it

Why does brewed coffee taste stale after a while?

Brewed coffee tastes stale after a while because it loses its freshness. The overall sensorial perception of the coffee brew is strongly related to its freshness. After being brewed, the loss of volatile compounds occurs fast. 2-Furfurylthiol (2-FFT), as a sulfur compound in coffee, has been established as one of the key aromas that contribute to the characteristic flavor of coffee and 86% of this compound is lost after 1 h brewed coffee storage at 40 °C (1). 

Oxidation is the main reason behind coffee tasting stale. All the coffee’s distinctive flavors are made up of highly volatile aromatic compounds that tend to oxidize immediately when they come in contact with oxygen.

The process of brewing coffee is the initial step in a long chain of chemical reactions that takes place. When the hot water infuses with the coffee grounds, they immediately release their intense fragrance, resulting in rapid loss of coffee oils and flavors.

Oxidation won’t stop even after brewing, as your cup of coffee is exposed to oxygen that continues to break down and react with other compounds. Besides the continuous oxidation, your coffee is still safe to drink; only the flavor and aroma are ones being compromised that are fading out.

This oxidation process occurs more rapidly at a higher temperature. That’s why the flavor of cold brew coffee lasts longer while a pot of coffee sitting around your stove or a hot plate of coffee maker becomes increasingly bitter. Although present in freshly brewed coffee, hydrogen peroxide increases in concentration through time and temperature. It is believed that H2O2 in the coffees may be coming from the reactions products formed during the roasting process and/or redox cycling of sulphuric compounds and polyphenolic constituents including chlorogenic acid. H2O2 is reactive in the body and could promote damage to DNA and host of other biomolecules (2).

 How long brewed coffee stays good in the refrigerator?

In the refrigerator, brewed coffee can stay good for 3 days to several weeks, depending on its composition. When added with milk, brewed coffee has a shelf life of 3 days in the refrigerator in a closed glass bottle. The low temperature and protection against light and oxygen results in slowing down the oxidation process and making your coffee last longer. 

Black coffee can last longer, because the composition of the coffee, which is high in polyphenols, does not favor the growth of microorganisms. The shelf life is therefore limited by sensory perceptions. Some suggest that black coffee can stay for a week in the fridge. But brewing coffee more than your daily need doesn’t sound right. Unless you plan to make cold brew. Due to the formation of hydrogen peroxide and its toxicity, it is not recommended (2).

Cold-brew can be stored in an airtight jar in the fridge for no more than 2 weeks. But it is recommended to store for 2 days, or to limit storage days at a minimum, due to the microbiological stability. The acidity of the brew will also be increased by time, as well as oxidation (3). This is a more commonly practiced method of cold brew lovers; they fill up a jar of cold brew concentrate and dilute it with water or milk as per their liking.

As mentioned before, brewing coffee and storing it at a lower temperature tends to extend the shelf life and flavor profile of your brewed coffee.

Is a one-day-old leftover coffee safe for consumption?

Drinking one-day-old coffee is safe. According to studies, when coffee is brewed following good hygiene practices, packed safely from microbial contamination and stored in sterilized packages, it can be stored for more than one day at room temperature (7). 

However, a study of Clemson University showed that the refrigerated shelf life of hot and cold brewed coffee is limited not by microbial stability, but rather by deterioration in sensory attributes. The microbial count remained <25 CFU/mL for both the total aerobic count, and for the psychrotrophic count after 42 days of refrigerated storage (5).

Milk-based coffee is not fit to consume after being out at room temperature for more than two hours let alone being a day old. Even if it was refrigerated, it is best to dump and make a new batch.

How long does caffeine stay in brewed coffee?

Caffeine stays in brewed coffee even after long periods of storage. Even at room temperature, the caffeine in brewed drinks is not totally eliminated after 30 days, differently from other compounds (7). Caffeine is an alkaloid that is thermally stable. Some of it is lost during the roasting process, but a small part may be lost during the brewing process (4).

However, a study of Clemson University showed that the amount of caffeine significantly decreased in refrigerated samples of brewed coffee for 42 days (5).

Conclusion

In this brief guide, we answered ‘how long can coffee sit out?’ Also, we have seen the changes that occur in coffee and also the factors that play a role in this.

Hopefully, you found this guide helpful. In case of any other queries or comments, please do let us know.

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