Crema：濃縮咖啡中神秘的泡沫藝術 | Crema: The Beauty on the Surface of Espresso

 

Crema是濃縮咖啡表面那層金棕色的細膩泡沫，這層泡沫由咖啡豆在烘焙過程中釋放的二氧化碳經過高壓萃取後形成。當水在高壓環境下被迫穿過咖啡粉，溶解出大量二氧化碳，隨後釋放的氣泡聚集在咖啡表面，形成Crema。

這層泡沫在濃縮咖啡中之所以能形成，與咖啡中的表面活性劑有關。這些活性劑來自於咖啡中的碳水化合物和蛋白質，它們能破壞水的表面張力，穩定並強化氣泡結構，從而形成持久且穩固的Crema。雖然摩卡壺和一些手沖方式（如Aeropress）也能產生Crema，但濃縮咖啡的高壓條件使其產生更多且更穩定的泡沫。

Crema的味道與功能

雖然Crema的外觀誘人，但它的味道往往比濃縮咖啡的其他部分要苦澀且乾燥。這是因為Crema中含有較多的二氧化碳，且甜味化合物較少。許多人會將Crema攪拌到咖啡中，使整杯咖啡的風味更均衡，或直接去掉它，以減少苦味和乾澀感。

Crema對咖啡的資訊反映

Crema的多寡可以透露出咖啡的新鮮度、烘焙度及萃取水平。例如，新鮮的咖啡豆儲存的二氧化碳更多，因此會產生更多Crema；而深焙咖啡由於烘焙時間較長，含有更多的二氧化碳，所以通常也會形成較多的Crema。相反地，若Crema快速消失或變薄，可能是因為萃取不足或水流不均（通道效應），導致濃縮咖啡的粘稠度不夠，泡沫無法維持。

虎斑紋與攪拌Crema

油脂對Crema的影響咖啡中的油脂會抑制泡沫的形成，因此油脂含量較低的咖啡豆（如羅布斯塔）能產生更多Crema。即使在高油脂的阿拉比卡咖啡豆中，高壓萃取也會使油脂與水混合，形成穩定的乳狀液體，這樣油脂對Crema的負面影響會減弱。壓力越高，Crema的持續時間越長。

Crema的顏色與持久性

Crema的顏色與咖啡的烘焙程度和萃取時間有直接關係。深焙咖啡的Crema顏色較深，萃取時間越長，Crema的顏色越深。反之，淺焙咖啡或快速萃取的咖啡會產生較淺的Crema。咖啡的粘稠度與Crema的持久性也有關，萃取越充分，咖啡越粘稠，Crema就越持久。

如何提升Crema的產生

若想在濃縮咖啡中產生更多的Crema，應使用新鮮烘焙的咖啡豆，因為咖啡中的二氧化碳會隨著時間的推移逐漸消散。研磨後立即沖煮咖啡也能保留更多氣體。深焙咖啡則因含有更多二氧化碳，能產生更豐富的Crema。

Crema的重要性

當製作濃縮咖啡時，產生Crema是正常的過程。如果Crema不足或缺乏，可能意味著製作過程中的某個環節出現了問題，如研磨過粗或咖啡豆不夠新鮮。雖然Crema不能直接告訴你咖啡的風味，但它確實提供了有關新鮮度和萃取的訊息，並增強了咖啡的視覺吸引力。

---

Crema, the golden-brown foam on top of espresso, is formed when carbon dioxide, released during the coffee roasting process, is extracted under high pressure. As pressurized water passes through the coffee grounds, it dissolves large amounts of CO2, which then escapes as tiny bubbles when the brew enters the cup, creating the distinctive crema layer.

This foam appears due to surface-active agents in coffee, primarily carbohydrates and proteins, which stabilize the bubbles and reinforce the structure of crema. While moka pots and some Aeropress methods can produce small amounts of crema, espresso's high pressure results in a more abundant and stable crema.

Taste and Function of Crema

While crema looks appealing, its taste tends to be more bitter and dry than the rest of the espresso due to its higher CO2 content and lack of sweet compounds. Many people stir the crema into the coffee to balance the flavors, while others prefer to skim it off to reduce bitterness and dryness.

What Crema Can Tell You About Coffee

The amount of crema can provide insight into the coffee's freshness, roast level, and extraction process. Freshly roasted beans contain more CO2, resulting in more crema, while darker roasts also produce more crema due to the longer roasting time. If the crema disappears quickly, it could indicate under-extraction or uneven water flow, which weakens the coffee’s viscosity and makes the foam unstable.

Tiger Stripes and Stirring Crema

In darker roasts, crema may display tiger stripes or spots, which are natural patterns caused by high concentrations of coffee particles during extraction. While beautiful, they are no cause for concern. Additionally, since crema has a stronger, more bitter taste, many choose to stir it into the espresso for a more balanced flavor, or skim it off entirely for a smoother taste.

The Impact of Coffee Oils on Crema

Oils in coffee act as anti-foams, reducing crema formation. This is why Robusta beans, which contain less oil, tend to produce more crema. In high-pressure espresso extraction, the oils are emulsified with water, which minimizes their negative impact on foam. Higher pressure also helps prolong crema’s lifespan.

Color and Longevity of Crema

Crema’s color correlates with the roast level and extraction time. Darker roasts and longer extractions result in darker crema, while lighter roasts or faster extractions yield lighter crema. The viscosity of the coffee also plays a role in crema’s longevity—the more viscous the coffee, the longer the crema lasts.

How to Enhance Crema Production

To produce more crema, use freshly roasted beans, as CO2 dissipates over time. Brew the coffee immediately after grinding to retain more gases. Darker roasts will naturally produce more crema due to higher CO2 content.

Does Crema Matter?

Crema is an essential part of espresso, and its absence may indicate issues with the brewing process, such as stale beans or improper grind size. While crema can provide clues about the coffee’s freshness and extraction, it cannot reveal the flavor. However, its visual appeal and contribution to the overall sensory experience make it an integral aspect of espresso.