How to Judge Coffee Bean Freshness Basic Coffee Knowledge What Causes Coffee Beans to Lose Freshness

The quality of coffee beans is crucial for a good cup of coffee. Stale beans taste completely flavorless, with dull acidity that lacks brightness and liveliness. There are many reasons why coffee beans lose freshness, including improper storage and the beans themselves being old. Whatever the reason, you need to learn how to judge the freshness of coffee beans. Let FrontStreet Coffee teach you for free.

Understanding Oily Coffee Beans

Have you seen coffee beans with an oily appearance? Why do some coffee beans look oily and glossy on the surface while others appear "dry and comfortable" without being greasy? What is the relationship between coffee bean "oiling" and freshness? Should we choose coffee beans that appear "oily" or "non-oily"?

Not Actually Oil

The "oil" evenly distributed on the surface of coffee beans is not actually "grease" but a water-soluble organic substance that appears oily. "Coffee oil" itself contains many coffee aromatic components and can dissolve in water, which is why your brewed coffee doesn't have a layer of grease floating on top.

Two Reasons for "Oily Beans"

Two factors cause "oily beans": a) stale light roast beans b) fresh dark roast beans. Let's explore these in detail.

a) Stale Light Roast Beans

"Light roast beans" with lighter roasting levels appear light brown and have a dry surface after roasting, without showing oil. About five days after roasting (this may shorten to one or two days during hot summer months), they begin to show "spotting oil" phenomenon (oil droplets appearing on one side of the coffee beans). Please note: a small amount of "spotting oil" doesn't indicate staleness; sometimes it actually represents the peak flavor state of light roast coffee beans. If they continue to sit out, after more than two weeks from roasting, the surface of light roast beans gradually develops a uniform, thin, glossy layer. The smell is no longer sweet and fragrant but carries a rancid oil odor. At this point, the flavor of "light roast beans" has declined, and you should avoid purchasing them.

b) Fresh Dark Roast Beans

"Dark roast beans" with deeper roasting levels appear dark brown and show a slight glossiness immediately after roasting. They begin to "oil" significantly on the surface from the first to the second day after roasting. The glossy appearance of "dark roast beans" not only doesn't indicate staleness but quite the opposite—dark roast beans will gradually lose their surface gloss after three weeks from roasting, eventually becoming dry, stale beans. Therefore, if you see coffee beans that appear dry and non-oily but have a dark brown color, please pay special attention to whether they are marked with a roasting date, as they are very likely already spoiled stale beans.

Methods for Determining Coffee Bean Freshness

Even stale "light roast beans" with oily surfaces will gradually dry out after long-term storage (such as three months), eventually returning to a dry, non-oily appearance. This shows that whether the surface appears oily is only a reference for judging coffee bean freshness, not an absolute indicator.

How Should We Determine Coffee Bean Freshness?

First, purchase from professional coffee roasters who clearly mark dates on their products, have brand credibility, and emphasize fresh roasting. Additionally, quality coffee packaging bags usually feature a "one-way degassing valve" (a small button-like hole on the top of the coffee bag) design to allow coffee beans to release naturally produced carbon dioxide. Point the one-way degassing valve toward your nose, gently squeeze the coffee bean bag, and smell the gas that comes out. If it's a captivating, rich coffee aroma, the freshness is still good. Conversely, if it doesn't smell fragrant enough or even has a rancid oil odor, it indicates this coffee has long spoiled and gone stale, and you should avoid purchasing it.

How to Determine Coffee Bean Freshness: Three Steps

There are three steps to determine coffee bean freshness: smell, look, and peel.

Smell:

Bring the coffee beans close to your nose and take a deep sniff. Can you clearly smell the aroma of the coffee beans? If so, it represents that the coffee beans are fresh enough. Conversely, if the aroma is weak or has already started to show a greasy smell, it indicates these coffee beans are completely stale.

Look:

Pour the coffee beans into your hand and spread them out to observe. Confirm the origin and variety of the coffee beans, and also check whether the roasting is uniform.

Peel:

Take a single coffee bean and try to peel it open with your hands. If the coffee beans are fresh enough, you should be able to peel them open easily, and there will be a crisp sound and feeling. If the coffee beans are not fresh, you'll find that you must exert considerable effort to peel open a single bean.

Additionally, the most common indicator is: whether there are enough rich bubbles during brewing!

Abundant Bubbles Indicate Freshness

Freshly roasted coffee beans contain large amounts of gas within the bean body and have active respiration. During extraction, the gases released from the beans create the wonderful, abundant bubbles we see. There's a vivid descriptive term for this: "blooming." Yes, when fresh coffee beans are extracted, clusters of rich bubbles are like the flowers of this season, blooming.

Accompanying this is the rich aroma of fresh coffee beans.

Deeper Analysis of Bubble Abundance

During extraction, the abundance of bubbles is positively correlated with freshness—the fresher the beans, the more bubbles produced. However, there's a prerequisite here: this applies to the same coffee bean. Specifically, it means the same green beans, same roast, same operation.

Between different coffee beans, or between different roast levels of the same coffee bean, or between different operational parameters of the same coffee bean, the abundance of bubbles will show different performance.

In simple terms: for the same coffee bean, the fresher it is, the richer the bubbles; for the same coffee bean, dark roast produces more abundant bubbles than light roast.

And between different coffee beans, setting aside differences in roast level and other factors, they will also show differences in hydrophilicity from their own structural aspects, most intuitively reflected in the speed of water absorption and the degree of bubbling.

Extraction Adjustment Suggestions

For the same coffee bean, if the current extraction method is not ideal, consider: increasing the amount of coffee grounds to increase the thickness of the coffee bed and extend the contact time between coffee grounds and water; raising the extraction water temperature to further stimulate the activity of the coffee beans; reducing the grind size to make the powder finer and increase the contact area between coffee grounds and water molecules.

Of course, the above suggestions are aimed at fresh coffee beans.

Every adjustment of extraction factors will have a certain impact on the final coffee taste. For the taste of the final cup, it still depends on the maker's judgment.

Furthermore, when we judge fresh coffee beans, we should also consider whether the green beans are fresh.

A good cup of coffee, 60% depends on the quality of green beans. As coffee professionals, we should broaden our perspective and try to learn more about the entire process from coffee seeds to cups, building a complete coffee knowledge system. This will be helpful for the work we do in our own segment. After all, roasters roast according to bean characteristics, while baristas brew based on bean characteristics and roasting philosophy.

Freshness of Green Beans

The same bean variety, estate, altitude, and cultivation method—new harvest green beans and old beans show significant differences in dry aroma and wet aroma. Because coffee is also a type of agricultural product, freshness is very important for coffee.

Generally, coffee beans harvested in the current year are called "new crop" (New Crop), those harvested the year before are called "past crop" (Past Crop), and those stored for more than a year are called "old crop" (Old Crop). The main reason for this distinction is the moisture content of green beans. New crop beans have higher moisture content (usually between 11%-13%) and mostly appear deep green in color, while past crop beans (10%-11% moisture) and old crop beans (9%-10% moisture) appear lighter green in color, with lighter weight and texture, lacking the surface gloss and tactile feel of new beans. Of course, different processing methods and origins, as well as varieties of green beans, will vary.

New Beans: Surface with Rich Gloss and Tactile Feel

Changes in Green Bean Freshness:

New crop beans > past crop beans > old crop beans > aged beans

New Crop Beans:

Green beans harvested within one year

Past Crop Beans:

More than one year...

Old Crop Beans:

More than two years

Aged Beans:

Matured green beans.

For example, after one year at normal room temperature, the moisture content of green beans will drop below 10%. Freshly processed green beans are blue-green/green in color, but as time passes, the color of green beans will gradually turn light green, white, or yellow. And as the aging process extends, the aroma of green beans will change from grassy and spicy to hay or rice-like aromas. After even longer periods, they will have no aroma at all.

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