Factors Affecting Coffee Extraction: The Impact of Water Temperature

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FrontStreet Coffee - Sharing the Factors Affecting Coffee Extraction

1. Coffee-to-Water Ratio:

Simply put, in the same 150ml cup, the higher the coffee content, the stronger the taste, while the more water content, the lighter the taste. For example, with general drip coffee, we want a mellow and refreshing taste, so we use a lower coffee-to-water ratio. The purpose of espresso is to extract concentrated syrup-like coffee in a short time, so we need to use a higher coffee-to-water ratio. For a cup of coffee, we expect the weight of coffee substances released into the water to be approximately 18-22% of the coffee's weight. This can also be described as the coffee-to-water exchange rate, which we hope to fall between 18-22%. To achieve this standard, it's generally recommended to use a coffee-to-water ratio of 1:15. Of course, this number is quite flexible, and we often adjust the coffee-to-water ratio according to personal taste, water temperature, grind size, and roast degree, finding the most appropriate ratio that suits our preferences through multiple fine-tuning.

2. Grind Size and Extraction Time:

Coarser grinds require longer steeping time to allow coffee flavors to be released into the water. Extraction methods using steeping, such as French press or siphon, are more ideal for coarsely ground coffee because the contact surface between coffee and water is smaller. If water passes through too quickly, it's difficult for coffee to have adequate contact time to dissolve flavors into the water. On the other hand, when using finely ground coffee, we need to conserve the contact time between coffee and water. If using steeping methods, it may actually lead to over-extraction. Therefore, we generally use methods that allow water to quickly contact coffee and flow out rapidly for extraction, such as pour-over or espresso extraction.

As for how much to adjust the grind size? Because the equipment used by everyone varies, it wouldn't be fair to say which grinder or coffee machine is more standard. It's more recommended to adjust the coarseness according to the extraction method and personal taste.

3. Proper Extraction Operations

1. Estimate the coffee grind size and the contact time between coffee and water. As mentioned in the previous section, coarse and fine grinds are suitable for different brewing methods. Slight carelessness can lead to under-extraction or over-extraction.
2. Water temperature. Higher temperatures shorten extraction time, while lower temperatures require longer extraction time to achieve ideal extraction. For water temperature, we generally recommend staying between 85-94 degrees Celsius. In other words, boiling water is not an ideal choice for coffee extraction because excessive temperature seriously shortens extraction time, often leading to over-extraction, which reduces aroma, deteriorates flavor, and makes the mouthfeel heavy due to over-extraction.
3. Pre-infusion. To ensure coffee can steep evenly, we often first wet the coffee, letting water flow through the coffee once to even out the contact surface between coffee and water, then proceed with formal extraction. We often use this technique when using a pour-over kettle, and some call this technique "blooming." Similarly, when using a siphon, we also use this technique to level the contact surface between water and coffee to achieve balanced extraction.

4. Ideal Extraction Methods

1. Immersion Method: The most representative is undoubtedly the French press. Let coffee steep in hot water for a period of time, then filter it out.
2. Boiling Method: People who often watch European period films should have seen the main characters put coffee and water in a pot and place it directly on the stove to cook. Using slow heating and thermal convection in water to extract coffee.
3. Percolation Method: The principle of the Moka pot belongs to the percolation method. Heat on the stove to force hot steam into the metal tube, flow through evenly distributed coffee in the filter, and finally the extracted coffee liquid flows out from the spout of the upper pot.
4. Drip Method: Both pour-over and American coffee machines belong to this method, dripping hot water into coffee, using the physical property of water flowing downward to extract coffee from top to bottom.
5. Vacuum Filtration Method: The siphon is the most representative tool for this extraction method. Using the principle of thermal expansion and contraction and vaporization to pump hot water from the lower pot to the upper pot, after extraction is complete, cool the lower pot, then use vacuum suction to draw water back to the lower pot.

5. Good Water Quality

Water accounts for 98% of the weight in a cup of coffee! So we can say that water quality affects 98% of the coffee. Besides pure water, the water we generally use contains many kinds of minerals and, of course, some microorganisms. Because coffee is very sensitive, too many or too few minerals can affect the taste of coffee. If mineral content is too high, it can even damage our equipment (especially espresso machines, as calcium deposits are killers of machines). Therefore, water softening treatment and filtration are very important.

Important Notice :

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