title: "一次手磨咖啡体验" categories:
上周六 (2019/11/16) 在学校北区咖啡馆体验了一次手磨咖啡, 简单地记录一下. 也叫手冲咖啡.
主办方提供的器材如图
具体流程:
关于 "萃取", 高中时萃取被定义为液液萃取, 第一次见到这个操作觉得这不叫萃取, 但事实上还有固液萃取...
整套方法应该是 1750 年左右法国人想出来的, 在 espresso 出现之前最好的方法.
Around 1750, the French came up with the most important advance before espresso: the drip pot, in which hot water was poured onto a bed of grounds and allowed to pass through into a separate chamber. This invention did three things: it kept the temperature of the extracting water below the boil, it limited the contact time between water and ground coffee to a matter of a few minutes, and it produced a sedimentless brew that would keep for a while without getting stronger. The limits on brewing temperature and time meant a less complete extraction of the coffee. This reduced the bitterness and astringency, and allowed the other elements of coffee flavor more prominence, the tartness and aroma that were more appealing to European tastes.
用这种方法冲出来的咖啡萃取程度有限, 这一点喝手磨咖啡和机磨咖啡可以很明显地感受出来, 机磨咖啡浓郁苦涩得多.
主办方的回答道: 手磨咖啡没有油脂, 一般不加奶泡; 而机磨咖啡 (意式浓缩咖啡, espresso) 表层有一层厚厚的油脂, 从而可以把奶泡托起来拉花.
True espresso is made very quickly, in about 30 seconds. A piston or spring or electrical pump drives 200ºF/93ºC water through finely ground coffee at 9 atmospheres of pressure. (Inexpensive household machines rely on excessively hot steam, develop far less pressure, and take longer to brew, so the result is relatively thin and harsh.) The proportion of ground coffee is three to four times the amount used in unpressurized brewing, and deposits three to four times the concentration of coffee materials in the brew, creating a substantial, velvety body and intense flavor. These extracted materials include a relatively large amount of coffee oils, which the high pressure forces from the bean particles to form a creamy emulsion of tiny droplets, and which contribute to the slow, prolonged release of coffee flavor in the mouth, long after the last sip. Another unique feature of espresso is the crema, the remarkably stable, creamy foam that develops from the brew and covers its surface. It's the product of carbon dioxide gas still trapped in the ground coffee, and the mixture of dissolved and suspended carbohydrates, proteins, phenolic materials, and large pigment aggregates, all of which bond in one way or another to each other and hold the bubble walls together.
The key to proper coffee grinding is obtaining a fairly consistent particle size that's appropriate to the brewing method. The smaller the particle size, the greater the surface area of bean exposed to the water, and the faster its contents are extracted. Too great a range of particle sizes makes it hard to control the extraction during brewing. Small particles may be overextracted and large ones underextracted, and the resulting brew can be both bitter and weak. The common propellor grinder smashes all the bean pieces until the machine is stopped, no matter how small the pieces get, so coarse and medium grinds end up containing some fine powder. More expensive burr grinders allow small pieces to escape through grooves in the grinding surfaces, and give a more even particle size.
咖啡磨好后最好是颗粒粗细恰当而且大小一致. 尺寸差别太大的话难以控制萃取结果; 过小的颗粒容易过度萃取, 过大的则可能萃取不足, 结果冲出来的咖啡会苦而无味. 这一段主要是针对选购器械而言的, 给定器械后它能磨出什么样的我们就只能用什么样的.
Brewing is the extraction into water of desirable substances from the coffee bean, in amounts that produce a balanced, pleasing drink. These substances include many aroma and taste compounds, as well as browning pigments that provide color (almost a third of the total extract) and cell-wall carbohydrates that provide body (also almost a third). The flavor, color, and body of the finished drink are determined by how much ground coffee is used for a given volume of water, and by what proportion of that coffee is extracted into the water. Inadequate extraction and a watery, acid brew are caused by grinding the beans too coarsely, so that flavor is left inside the particles, by too brief a contact time between coffee and water, or by too low a brewing temperature. Overextraction and a harsh, bitter brew result from an excessively fine grind, or long contact time, or high brewing temperature.
在萃取之前要铺上滤纸, 主办方的建议是折叠成类似菊形滤纸的样子, 不要让滤纸贴着滤杯边缘 (这会导致咖啡经过滤纸的时间变短, 萃取不足). 加入的咖啡粉的量可以由带刻度的勺子控制.
为了恰当地萃取咖啡, 注水的速度要有所控制. 有种说法是, 手磨咖啡的萃取大体分为 3 个阶段, 其中第 1 个阶段萃取出来的咖啡最浓, 后面依次递减, 咖啡也更澄澈.
主办方给出的操作方案是: 先加水到差不多没过咖啡粉, 等滤杯中的液面快见底时再加水, 如此反复几次. 具体什么时候加水可以自行控制, 比如液面一下降就加水, 这样的话由于水的压强一直维持在较高的水平, 萃取得比较快, 可能会导致萃取不足. 而如果萃取的时间太长 (或加水次数过多) 会导致过度萃取, 咖啡变酸.
The ideal brewing temperature for any style of coffee is 190–200ºF/85–93ºC; anything higher extracts bitter compounds too quickly. For a standard cup of American coffee, the usual brewing time ranges from 1 to 3 minutes for a fine grind, to 6 to 8 minutes for a coarse grind.
打奶泡 (milk foams) 并不是这次体验的主题, 只是顺带而已.
A foam is a portion of liquid filled with air bubbles, a moist, light mass that holds its shape. A meringue is a foam of egg whites, and whipped cream is a foam of cream. Milk foams are more fragile than egg foams and whipped cream, and are generally made immediately before serving, usually as a topping for coffee drinks. They prevent a skin from forming on the drink, and keep it hot by insulating it and preventing evaporative cooling.
Milk owes its foaming power to its proteins, which collect in a thin layer around the pockets of air, isolate them, and prevent the water's strong cohesive forces from popping the bubbles. Egg foams are also stabilized by proteins, while the foam formed by whipping cream is stabilized by fat. Milk foams are more fragile and short-lived than egg foams because milk's proteins are sparse—just 3% of the milk's weight, where egg white is 10% protein—and two-thirds of the milk proteins are resistant to being unfolded and coagulated into a solid network, while most of the egg proteins readily do so. However, heat around 160ºF/70ºC does unfold the whey proteins (barely 1% of milk's weight). And if they unfold at the air-water boundary of a bubble wall, then the force imbalance does cause the proteins to bond to each other and briefly stabilize the foam.
Some milks are better suited to foaming than others. Because the whey proteins are the critical stabilizers, milks that are fortified with added protein—usually reduced-fat and skim milks—are most easily foamed. Fullfat foams, on the other hand, are fuller in texture and flavor. Milk should always be as fresh as possible, since milk that has begun to sour can curdle when heated.
这次做奶泡主办方提供的是全脂牛奶, 我问原因的时候他知道蛋白质是打出奶泡的关键, 但不清楚脂肪有什么用 (好像还说脱脂牛奶不能打, 最好用全脂牛奶). 事实上按照 McGee 的观点, 低脂和脱脂牛奶由于通常蛋白质更多更容易打出奶泡, 脂肪应该主要是为了好喝 (带适量脂肪的东西总是更好吃一些).
Milk foams are usually made with the help of the steam nozzle on an espresso coffee machine. Steaming milk accomplishes two essential things simultaneously: it introduces bubbles into the milk, and it heats the bubbles enough to unfold and coagulate the whey proteins into a stabilizing web. Steam itself does not make bubbles: it is water vapor, and simply condenses into the colder water of the milk. Steam makes bubbles by splashing milk and air together, and it does this most efficiently when the nozzle is just below the milk surface.
One factor that makes steaming tricky is that very hot milk doesn't hold its foam well. A foam collapses when gravity pulls the liquid out of the bubble walls, and the hotter the liquid, the faster it drains. So you have to use a large enough volume of cold milk—at least 2⁄3 cup/150 ml—to make sure that the milk doesn't heat up too fast and become too runny before the foam forms.
To get a good volume of milk foam from the steam attachment on an espresso machine:
To foam a small volume of milk without steam, separate the foaming and heating steps:
打奶泡的关键就是打出奶泡后通过适当地加热维持奶泡. 不过这次做奶泡条件有限, 就没有加热这个环节了, 于是奶泡很难维持住, 喝自己打的奶泡和机打的奶泡对比还是非常明显的. 这次的器具就是上文提到的 plunger-style coffee maker.
当然了, 是现磨现喝的.
Freshly brewed coffee is best enjoyed immediately—its flavor is evanescent. The ideal drinking temperature is around 140ºF/60ºC, where a sip won't scald the mouth, and the coffee's full aroma comes out. Because it cools in the cup, coffee is usually held in the pot just below the brewing temperature. High heat accelerates chemical reactions and the escape of volatile molecules, so coffee flavor changes noticeably after less than an hour in the pot; it becomes more acid and less aromatic. Coffee is best kept hot by retaining its original heat in a preheated, insulated, closed container, not on a hot plate that constantly supplies excessive heat from below while heat and aroma escape above.
Coffee has one of the most complex flavors of all our foods. At its base is a mouth-filling balance of acidity, bitterness, and astringency. A third or less of the bitterness is due to easily extracted caffeine, the rest to more slowly extracted phenolic compounds and browning pigments. Milk and cream reduce the astringency of coffee by providing proteins that bind to the tannic phenolic compounds, but these liquids also bind aroma molecules and weaken the overall coffee flavor.
中学时听说喝 espresso 不加奶和糖后, 每次去咖啡店必然头铁点 espresso, 觉得这么喝才正派, 最后倒是习惯了这种苦味 (这次同时来体验的 3 名同学中, 有 2 名表示手磨咖啡爆炸苦, 显然是之前从没喝过 espresso 的), 却依然没有喜欢上. 于是现在一般点加奶的咖啡, 加奶可以减少涩的感觉, 但是却减弱了咖啡的香味和整体风味.
向山进发 S3E6 讲述了完整的流程, 可以观看. (2020/6/24)
参考
McGee, H. (2004). On food and cooking: the science and lore of the kitchen. Simon and Schuster. pp. 26-27, 441-448.
Further Reading
回形针PaperClip. (2020, Dec 3). 速溶咖啡为什么这么难喝?. bilibili.