What Does Coffee Bean Silver Skin Taste Like? Does It Affect Coffee Flavor?

Sometimes, when we grind coffee beans into powder, we may notice some yellowish-white debris mixed in. Some of you might wonder: what are these white fragments? Why do some beans have many while others have none? Will they affect the taste of our brewed coffee if we don't remove them?

The Last "Clothing" of Coffee Beans

These conspicuous white crumbs mixed in the coffee powder are actually the silver skin that wraps around the coffee beans—the final "clothing" that green coffee beans wear before entering the roasting oven.

FrontStreet Coffee has previously shared about the structure of coffee cherries: skin, pulp, pectin layer, parchment, silver skin, and the coffee bean itself. If we observe green beans, we can find that the silver skin of naturally processed coffee is typically yellowish-brown, while that of washed processed beans is generally off-white and semi-transparent, tightly wrapping around the coffee bean. Similar to peanuts, this layer of silver skin cannot withstand the excessive expansion of the beans during the roasting process and separates from them.

Why Does It Still Remain If It Has Separated?

Although the silver skin falls off during roasting, some coffee beans still retain traces of it. The amount of residual silver skin is closely related to the processing method of the coffee beans. If you often purchase different types of coffee beans, you'll notice that some beans have a "white line" in the middle while others don't.

You can observe FrontStreet Coffee's image below. The biggest difference between the two types of coffee beans on the surface is the "white line" in the middle of the beans.

This is because during the natural processing of coffee beans, the silver skin remains relatively intact and can be peeled off in one piece during roasting, leaving only a tiny bit at the center of the bean. However, washed processed coffee beans cannot retain a complete silver skin like naturally processed ones, so during roasting, they only detach in small pieces. The remaining silver skin that hasn't fallen off in the middle becomes what we see as the "white line."

Therefore, observant coffee enthusiasts can roughly determine whether a bean is naturally or washed processed by whether it has an obvious "white line."

The above shows cross-sections of coffee beans processed by three different methods. We can easily find that each processing method retains some silver skin to varying degrees, and those with more silver skin are most likely washed processed beans.

Will Silver Skin Affect Coffee Flavor?

This should be the point of greatest curiosity for many friends. FrontStreet Coffee's roaster prepared a large bag of silver skin. Without further ado, let's start the "silver skin family bucket" experiment immediately! FrontStreet Coffee will use three methods—pour-over, tea bag, and coffee machine—to extract and taste what silver skin actually tastes like. (Since no specific bean type or roast level of silver skin was specified, this experiment uses "blended" silver skin.)

Pour-over Silver Skin:

FrontStreet Coffee used a 1:50 skin-to-water ratio, that is, 6 grams of silver skin infused with 300 grams of 90°C hot water. The brewed silver skin water smells very similar to genmaicha (brown rice green tea), but tastes more like wheat aroma. Although the overall mouthfeel is relatively light, it is very smooth and pleasant.

Silver Skin Tea:

FrontStreet Coffee took out a disposable tea bag, filled it with 3 grams of silver skin, placed it in a cup, poured in 210g of 95°C hot water, and let it steep for 15 minutes before tasting. Although the infused silver skin tea wasn't as aromatic as the pour-over version, it tasted more like Ku Ding tea, smooth and tasty without any astringency, which was quite pleasant.

Espresso Machine High-Pressure Extraction:

Since silver skin itself has an expanded, loose structure, FrontStreet Coffee was concerned it might spray wildly under high pressure, so we used a split portafilter for extraction. Extraction parameters: 4 grams of silver skin, extracting 36 grams of silver skin concentrate in 12 seconds. (Any more wouldn't fit in the portafilter basket, and using a tamper was pretty useless.)

Although the flow rate of the silver skin water was very fast, it didn't gush out like a fully opened faucet. In appearance, the silver skin tea made this way was much darker, very similar to dark roast pour-over coffee. Upon tasting, there was first a rich camellia fragrance, followed by a brief bitterness, and the aftertaste after swallowing was super long-lasting (seven to eight minutes).

Through extracting and tasting silver skin in three different ways, the results all tended to be consistent. The flavors presented by silver skin were almost all wheat aroma and genmaicha-like sensations, without any unpleasant tastes. The imagined astringency was completely absent. Therefore, we can conclude that the residual silver skin in coffee beans will not negatively affect the coffee; on the contrary, it can add more layers to the coffee.

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