"Introduction to Hand Brewing" Issue 5 | How to judge the freshness of coffee beans?

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Freshness is the key to delicious coffee.

More and more people are getting used to buying freshly roasted coffee beans directly from roasters, so there are many tips on how to identify the freshness of coffee beans.

How to judge the freshness of coffee grounds?

Among them, the most common one is:

Are there enough bubbles when brewing?

The abundance of bubbles indicates freshness

Freshly roasted coffee beans contain a lot of gas and have vigorous respiration. When they are extracted, the gas in the beans is released, and what we see are beautiful and plump bubbles. There is a very vivid adjective to describe it, "blooming". Yes, when fresh coffee beans are extracted, clusters of rich bubbles are like flowers in this season, blooming.

Accompanying it is the rich aroma of fresh coffee beans.

A deeper look into whether bubbles are abundant or not

During extraction, the richness of bubbles is positively correlated with freshness. The fresher, the more bubbles . However, there is a premise here, that is, for the same coffee bean. To be precise, it is the same raw bean, the same roasting, and the same operation.

The richness of bubbles will vary between different coffee beans, or between different roasting degrees of the same coffee bean, or between different operating coefficients of the same coffee bean.

To summarize simply: for the same coffee bean, the fresher it is, the richer the bubbles; for the same coffee bean, dark roasted ones will produce richer bubbles than light roasted ones.

Different coffee beans, apart from differences in roasting degree and other factors , will also show differences in hydrophilicity from the perspective of their own structure, which is most intuitively reflected in the speed of water absorption and the degree of foaming.

Tips for Adjusting Extraction

For the same coffee bean, if the existing extraction method is not ideal, you can consider: increasing the amount of coffee powder, increasing the thickness of the powder layer, and increasing the time the coffee powder combines with water; increasing the extraction water temperature to further stimulate the activity of the coffee beans; reducing the degree of grinding, grinding the powder finer, and increasing the contact area between the coffee powder and water molecules.

Of course, the above suggestions are for fresh coffee beans.

Adjusting each extraction factor will have a certain impact on the final coffee taste. The final taste of the cup still depends on the maker's control.

Also, when we judge the freshness of coffee beans, we also need to consider whether the raw beans are fresh?

60% of a good cup of coffee depends on the quality of raw beans. As a coffee practitioner, you should open up your mind and learn as much as possible about the entire process from coffee seeds to cups, and build a coffee knowledge system. This will help you in the process you are engaged in. After all, roasters roast according to the properties of beans, while baristas brew according to the properties of beans and roasting concepts.

Different degrees of freshness of green beans

With the same bean variety, farm, altitude, and planting method, the dry and wet aromas of new green beans and old beans are very different. Because coffee is also a crop, freshness is very important for coffee.

Generally speaking, fresh coffee beans harvested in the current year are called "New Corp", those harvested the year before are called "Old Corp", and those stored for more than a year are called "Old Corp". This distinction is mainly due to the moisture content of the raw beans, because new beans have a high moisture content (usually between 11% and 13%) and are mostly dark green in appearance, while old beans (moisture content 10% to 11%) and old beans (moisture content 9% to 10%) are lighter in appearance green, lighter in weight and texture, and not as shiny and tactile as the surface of new beans. Of course, different processing and refining methods, origins, and varieties of raw beans will be different.

New beans: shiny and tactile like the surface

Changes in the freshness of green beans:

New season beans > out-of-season beans > old beans > aged beans

New season beans: green beans harvested within one year

Overdue beans: more than one year old. . . .

Old Bean: More than two years

Aged beans: mature green beans.

For example, after one year at room temperature, the moisture content of raw beans will drop below 10%. The color of freshly processed raw beans is blue-green/green, but as time goes by, the color of the raw beans will gradually turn into light green, white or yellow. And as the cooking time increases, the aroma of the raw beans will change from grassy and spicy to hay or rice. If it takes longer, it will have no taste at all.

The ripe "coffee cherry" is refined and processed into green beans through washing or drying. The moisture content is usually between 9% and 13%. It is not easy to roast if the moisture content is too high or too low.

Generally, the moisture content of newly harvested washed green beans is around 11.5% to 12.5%. Semi-washed Mandheling may reach 13%, semi-washed Brazil 11% to 12%, and sun-dried Mocha has a wider range of about 9% to 12%.

Coffee can be drunk all year round, but high-quality coffee also has seasonal issues. In fact, coffee is the same as fruit, with its own seasonal production period, and there are seasonal and out-of-season coffee.

However, there are at least 60 countries in the world's three continents that produce coffee, and the production seasons in the northern and southern hemispheres are different, which increases the complexity of this issue. Coffee lovers can learn about the seasons of each producing area and buy fresh beans more easily if they pay more attention to coffee.

When the rainy season in the coffee producing area begins is related to the harvest time. The rainy season prompts the coffee trees to bloom and bear fruit, which takes about 6-9 months. When the coffee berries are ripe and turn red, they can be picked and peeled, washed and fermented, semi-washed or sun-dried (the moisture content of shelled beans reaches 12%), and then put into warehouses for ripening for 1-3 months. Finally, the seed shells are ground off and they can be exported.

In other words, after the coffee beans are harvested, it takes at least another 2-3 months to complete the tedious post-processing before they can be exported.

Generally speaking,

• In the northern hemisphere, the Central American production area or Aceh in Indonesia is the busiest harvest and post-processing period from February to March each year, so the beans of the season can be shipped to consumer countries around May to October.

• Brazil in the southern hemisphere is the busiest harvesting and post-processing period from May to July each year, and seasonal beans can be shipped from September to April of the following year.

• The harvest season of fresh beans in Africa is from May to October, so the beans of the season can be shipped to consumer countries from January to March of the following year;

• Colombia has fresh coffee berries harvested all year round

• In addition, if the producing country crosses the equator, the production area is distributed in the northern and southern hemispheres. For example, Kenya has two harvest seasons, that is, fresh beans are exported in all seasons. Kona in Hawaii is from August to January of the following year.

• Vietnam, Thailand, and Yunnan generally harvest fresh fruit from November to January of the following year.

• Papua Guinea: April to September every year

• The harvest period of Jamaican Blue Mountain coffee is from June to November each year.

The flavor and aroma will last for different periods of time depending on the storage method.

No matter how good the quality of green beans is, it will vary depending on the storage method and storage facilities. The best way is to maintain the indoor temperature at 15-18 degrees Celsius and the indoor humidity at 50%-60%. The wrong storage method will affect the flavor and aroma of the beans, and even cause them to deteriorate. Often, the green beans will fade, turn white, and become soggy.

White or yellow green beans: This is because the temperature in the storage place is too high or too dry, causing the moisture of the green beans to be absorbed by the air.

Green beans with wet surface: The humidity in the storage place is too high, and it is the rainy season. In serious cases, mold will appear on the surface of the beans.

Coffee Roasting | Old and New Beans

The moisture content of raw beans will affect the roasting time and the difficulty of control. Generally, new beans will take longer to roast and be more difficult to control than old beans.

Of course, the fresher the coffee beans are, the better. Fresh coffee beans are full of vitality. Semi-fresh coffee beans are energetic but a little bit steady. After eight months, the vitality of coffee beans is lost.

Coffee is considered a futures product and will be marked with the year of production. Generally speaking, it will cross years. At the beginning of the year, people drink last year's and the year before last's batches, and then gradually move on to last year's and this year's batches. For example, at the beginning of 2018, people usually drink the 2016-17 batches, and a few months later, they can drink the 2017-18 batches. There are also some coffee bean traders who do not use cross-year divisions as the batch standard. For example, 90+ uses a single year as the batch standard.

From the above, we can see that if the coffee bean dealer has stockpiled old goods, perhaps from batches 3 or 4 years ago, which have been stored for a long time, then even if such coffee beans are stored properly, the flavor will definitely be different from fresh batches of beans. As for how big the difference is, it depends on the storage level and the oxidation speed of the beans themselves. Aged beans are another topic - that is a carefully managed coffee maturation process, but not all coffee beans are suitable for aging!

Green beans that are more than one year old are old and tasteless. However, the above comments only apply to general coffee beans under normal storage conditions. They are not applicable to specially treated beans and special storage environments, such as low-caffeine treatment, aging, wind stain treatment, etc., which is another area of ​​appreciation.

Shops selling specialty coffee often prefer fresher batches. After all, time is terrible and it is unknown how much of the coffee's flavor it will take away. Roasters certainly don't want the green beans they buy to have only 50% of the flavor left. This is like throwing money down the drain.

From the above, we can know that for raw beans to be fresh, there must be no mistakes in production, transportation, and storage, otherwise the coffee beans will be stale.

Under the premise of proper storage, there is no fixed formula for the time and the tasting period, but it is related to the bean type and processing method. Washed beans with bright flavors, such as Kenya, Costa Rica, and Kona, are indeed not suitable for long-term storage. Fresh new beans have the most fragrant original flavor of coffee fruits.

Finally, the surface of the coffee beans is used to judge the freshness

What is the relationship between coffee bean "oiliness" and freshness? Should we buy coffee beans that have "oiliness" or "no oil" on the surface?

Coffee oil is not oil:

These "oils" evenly distributed on the surface of coffee beans are actually not "grease", but a water-soluble organic substance that looks like grease. "Coffee oil" itself contains many coffee aromatic components and can be dissolved in water, so the surface of your brewed coffee will not be covered with a layer of greasy grease.

Two reasons cause "oil beans"

a) Stale lightly roasted beans

"Light roasted beans" are roasted at a lighter temperature and have a light brown appearance. After roasting, they are dry and do not produce oil. About five days after being roasted (it may be shortened to one or two days in the hot summer), they begin to produce "spotted oil" (dots of oil appear on one side of the coffee beans). Please note: a small amount of "spotted oil" does not mean that they are not fresh. Sometimes it is the peak state of the flavor of light roasted coffee beans. Continue to place them for more than two weeks after being roasted. A layer of uniform, thin and shiny oil will gradually appear on the surface of the light roasted beans. The smell is not sweet, but has a smell of oil. At this time, the flavor of "light roasted beans" has gone downhill and should be avoided.

b) Fresh dark roasted beans

Dark roasted beans, which are roasted at a deeper temperature and have a dark brown appearance, will have a slightly oily appearance after roasting, and will begin to "produce oil" on the surface from the first to the second day after being roasted. Dark roasted beans with a shiny appearance do not mean they are not fresh. On the contrary, the oily appearance of dark roasted beans will gradually dry up three weeks after being roasted, and finally become dry beans with stale taste. Therefore, if you see coffee beans that are dry and not oily , but have a dark brown appearance, please pay special attention to whether they are marked with the roasting date, as they are most likely stale beans that have gone bad.

Even if the "lightly roasted beans" are no longer fresh and have oil on the surface, they will gradually dry out after being left for a long time (such as three months) and finally return to a dry and non-oily appearance. It can be seen that whether the surface is oily is only a reference for judging the freshness of coffee beans, not an absolute. Therefore, most roasters clearly mark the roasting date. Everyone should choose professional coffee roasters with a reputable brand and emphasize fresh roasting.

Good coffee packaging bags usually have a "one-way exhaust valve" (a small button-shaped hole on the top of the coffee bag) design to allow the coffee beans to release the naturally produced carbon dioxide. Point the one-way exhaust valve to your nose, gently squeeze the coffee bean bag, and smell the gas that comes out. If it smells charming and fragrant coffee, then the freshness is fine. On the contrary, if it does not smell fragrant enough or even has a smell of rancid oil, it means that the coffee has already gone bad and should be avoided.