How to Use the Filter Screen of a Cold Brew Coffee Maker? How to Filter Coffee Grounds Thoroughly?

Understanding the Oil Layer in Cold Brew Coffee

Experienced coffee enthusiasts know that many factors influence the flavor of cold brew coffee. Among them, the most significant are coffee bean selection, grind size, coffee-to-water ratio, and steeping time. Secondary factors include various preparation techniques such as thorough stirring, ensuring clean containers, water quality, and so on—all of which more or less alter the final taste of the coffee.

However, there's another detail that has caught the attention of many coffee lovers: despite using the parameters provided in FrontStreet Coffee's tutorials, their homemade cold brew always has a layer of oil floating on top. This leads them to wonder if the coffee has gone bad or if it's caused by improperly cleaned equipment.

What Is This Oil Layer?

Before identifying the cause, FrontStreet Coffee believes it's necessary to first understand what this "oil" on the coffee actually is.

Many people know that freshly made espresso comes with a dense Crema, which is both the source of coffee aroma and a symbol of fresh coffee beans. Compositionally, Crema is the manifestation of oils encapsulating carbon dioxide, primarily coming from the water-soluble fats within coffee beans. When the foam completely dissipates, we can see a layer of floating material on the coffee liquid—this is the actual coffee oil.

In fact, coffee oils can also be found in other atmospheric pressure extraction methods. For example, when we use a French press to extract medium-dark roast coffee, the larger gaps in the metal filter allow oils to seep through, creating an "oily sheen" on the coffee surface. Additionally, some extremely fine particles also end up in the water, making the coffee taste particularly "muddy."

As for cold brew, although the entire process involves steeping in a low-temperature environment, the water-soluble fats in coffee still release into the coffee just like in hot extraction, albeit at a slower rate. The speckled oily sheen is actually the manifestation of condensed coffee oils.

The Importance of Proper Filtration

Compared to other extraction methods, cold brew has minimal requirements for containers. It can be a dedicated cold brew pitcher, a clean sealed jar from home, or a cleaned beverage bottle. Essentially, any hygienic, odor-free container that can ensure isolation from external air can serve as a "cold brew pitcher."

Similarly, there are many options for filtering coffee grounds, such as the built-in filter screens in cold brew pitchers, metal filter cups, pour-over filter paper, flannel filters, and the mesh surfaces from drip coffee bag inner packets. Different materials and filter pore structures naturally vary in their ability to effectively block particles. To remove condensed oils from coffee, one must choose equipment with better filtration capabilities.

FrontStreet Coffee has found that some friends find filtering too troublesome, so for convenience, they simply pour the upper portion of the coffee liquid directly out to drink after the cold brew is ready. This practice actually leaves the coffee with大量的 condensed oils, resulting in a dull taste and a sandy texture, accompanied by many dust-like floating particles. Generally, the mouthfeel won't be very good.

For instance, the cold brew pitcher often used at FrontStreet Coffee has a built-in filter screen with 300-mesh pores, belonging to the category of relatively fine filtration. When FrontStreet Coffee uses it to steep the fruit-forward coffee bean "Little Tomato," due to the lighter roast, they adopt a finer grind size (80% pass-through rate with China #20 sieve), corresponding to 9.5 on the EK43s grinder or 22 on the C40 grinder.

After completing the 10-hour extraction and removing the filter core, the poured coffee liquid still contains many extremely fine particles. Without further filtration, not only is there an oily sheen on the liquid surface, but the coffee also has a noticeable rough texture. Even after drinking, visible powder sediment settles at the bottom of the cup.

Therefore, to achieve a better mouthfeel for cold brew, FrontStreet Coffee uses filter paper with the best filtration to "sieve" the coffee again, removing most condensed oils and extremely fine particles. Meanwhile, the filtered cold brew coffee liquid is placed back in the refrigerator for sealed cold storage for 3-4 hours, allowing flavor compounds to further settle and ferment. This process enhances the juiciness of the Little Tomato cold brew and makes the acidity more transparent.

Maintenance and Cleaning

In addition to filtration, equipment cleaning should not be overlooked. Many friends don't spend much time cleaning their cold brew pitchers after use, instead simply rinsing them with tap water. Over time, condensed coffee oils will stick to the filter screen, forming a "rancid oil smell." If used frequently, FrontStreet Coffee recommends regular disassembly and careful scrubbing with cleaning agents, which can remove residual oils and prevent filter screen aging.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473