Espresso观念之Al’s Rule(艾尔铁则：甜蜜点公式)

　　2000年的3月，一切都因为那时还很菜的Mark Prince转贴了一篇报章花絮开始，讨论从意大利espresso的标准定义，到Mark的意大利见闻，最后有人搬出Schomer书中的章节，话题突然转到ristretto这个名词上……正当大家开始有点雾煞煞，怀疑东怀疑西的时候，Al Critzer(曾任职illy USA、Cimbali)加入了这个讨论串，他提供了一个经过业者大量测试的归纳结果，并且为ristretto做了批注。对他而言可能不感觉到什么特殊意义，因为一般相信这并非他个人独到的见解(他自己也说This info was passed on to me by Dr. illy and his disciples, so I guess it is an Italian way of thinking as well as the single most respected scientific mind in the field of espresso. )，他可能只是一个传播信息的好心人而已，但绝对是当时网络论坛的经典大事件。他告诉了一大堆有研究咖啡热情，却缺乏正确理论基础的人，一个可以朗朗上口的口诀。他所讲的那几段话，之后这些年经过千锤百炼，不但是欧美最有共识的espresso观念，甚至后来几乎所有能在网络上看到的萃取文献都以此为蓝本，被称为：Al's Rule，<艾尔铁则：甜蜜点公式>

　　原文如下：

　　It seems that everyone's close, but pretty much all around it. As I was trained, the perfect espresso is 30ml in 30sec. That's assuming that all other factors are in line. For longer extractions, the contact time of water to coffee would have to be lessened so that undesirable elements associated with overextraction wouldn't be present in the cup. With shorter extractions, the water to coffee contact time would have to be increased to ensure that underextraction doesn't occur. This is accomplished by grind adjustment. A good rule of thumb I have developed is this: For every 5ml of espresso above 30ml, subtract 1 sec of extract time. By this formula 1 1/2oz (45ml) would require 27sec extraction, 2oz (60ml) would require 24sec, etc. The same holds true in reverse. This will find the sweet spot in espresso regardless of volume in the cup (within reasonable limits of .75oz to 2.5oz), as you are optimizing extraction to the desirable elements, maintaining the balance between under- and overextraction. For some reason, grinder adjustment and it's crucial impact on espresso is the most difficult concept to explain and grasp in all the trainings I do.

　　大意是

　　以30cc/ 30sec得到一杯完美的Espresso的结果为出发点。这二个数值当然视豆子而定，烘焙方式、烘焙度、配方比例的差异自然会导致基准点的变动。

　　萃取量与萃取时间互为反比：

　　当萃取量越多的时候，咖啡粉与热水接触的时间必须越短(避免过度萃取)

　　反之，当萃取量缩减，咖啡粉与水接触时间要增加(避免萃取不足)

　　Al公式：每增加5cc的萃取量，萃取时间要减去1sec。反之，则要加上1sec。

　　例如，萃取量增加到45cc时，30-(45-30)÷5=27，萃取时间缩减为27sec。

　　萃取量60cc时，萃取时间变成24sec。

　　这个公式在0.75-2.5oz的Espresso合理限定内，都能迅速正确的猎取甜蜜点(Sweet Spot)，有效地抓到令人满意的成分，并维持过度萃取与萃取不足之间的恐怖平衡。控制的方式以调整研磨粗细为主要手段。

　　至于那个年代也有争议的ristretto定义，Al Critzer也顺便做了他的解释：

　　As to ristretto. This a different drink altogether. If your grinder is set for regular espresso, and you choose to stop the pour at 25ml, this is simply an underextracted espresso. You haven't hit the sweet spot yet. The " restricted" part referred to as ristretto is not so much related to volume as it is to water flow through the coffee puck. The ristretto that has been used for cuppings is a 25ml cup in 30-35sec. This extraction intensifies the organoleptic perceptions of the eyes, nose, taste buds and upper pallate to better isolate the positive attributes of a given blend. Where the positives are accentuated, the negatives are exacerbated as well. The extractions are characterized by a very thin mouse's tail with rich, dark brown crema. Most people don't drink this as their everyday drink, but it is helpful in developing blends. If you customarily drink 25ml (or 50ml doubles), your grinder should be adjusted accordingly. Damn, I did it again….

　　ristretto是一种跟正常espresso截然不同的饮料

　　如果研磨不变，用正常的espresso流速，提早结束萃取，比如说原先的30sec/ 30cc流速下，只取25cc，这就是一杯萃取不足的成果，因为还没到达甜蜜点

　　所谓的ristretto就是受限定的意思(restricted)，习惯作法是25cc/ 30-35sec

　　所有感官上能察觉的感受，包括眼睛看到的、鼻子闻到的、舌头尝到的，不论是好的味道，或是坏的味道，都被加重呈现

　　ristretto的表征是老鼠尾巴特别细，加上更深褐色的crema

　　大多数人不会每天喝这种东西，但是有利于仍在发展中的blend

　　如果你就是习惯要喝ristretto的人，不管是25cc或是50cc，那你的研磨就要去对应调整。怎么调整?一样啊，Al' Rule重新来过吧

　　Al Critzer当时在讨论串里与知名业者Dr. Joseph John(Josuma Coffee Company)的另一段对话也很经典：

　　Dr John,

　　you didn't mention if this was done with the single filter or double. I'm hoping it was with the single. I personally am of the opinion that any espresso (single) should not be less than 25ml. A 1/2 oz (15ml) espresso has proved impossible for me to make in any drinkable state.

　　这里Al等于是重申了他的公式是在setting work的最初，采用single basket冲煮的数据来作为推算的依归。也就是纵然你的店里平时出杯都是使用double滤器，single滤器仍然是设定的基准。而他个人经验看法中，任何espresso(指single)都不应该少于25cc。一杯15cc的espresso对他而言，是无法达到『可以喝』的状态(drinkable这个字离好喝还很遥远) ，这也等于对后来一些喜欢30cc double ristretto的人提前做出了忠告。