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Know your Rancilio Silvia.
Know
the limitations so they can work in your favor.
Water temperature
delivery: Silvia is not like a commercial machine in that it has only one boiler with only 2 simple mechanical thermostats one for brew and one for steam. Furthermore, the boiler is very small boiler (300 ml = 10 US fluid ounces) and so the temperature is affected by very small amounts of cold water introduced into it after each shot. To overcome, to some extent, these inherent limitations on water temperature stability, we can install a PID temperature control, insulation and other features which will reduce water and heat consumption and provide significant improvement in temperature stability and therefore better consistency in the shot produced by Silvia. However, even if we could control boiler temperature with 100% accuracy, there would still be some variation (1, 2, or 3 degrees Fahrenheit, 1 degree Fahrenheit = 0.566 Celsius ) in the water temperature at the puck because of other contributing factors such as varying temperature of metal at the
grouphead* or even change in room temperature. So even though we try to do the best we can with boiler temperature accuracy, we have to recognize that it
is not worth worrying about slight variations once you are within that range. You will get a better return on your investment of time if you pay close attention to all other factors that make for a good shot: fresh coffee, proper grind, proper dosing,
uniform extraction, proper extraction by time and volume and clean machine. Even in far more expensive machines with the E61 group head which is often held up as
extremely good, or in heat exchange espresso machines, there will still be variation in water temperature from shot to shot at the puck. (you can read more about Silvia temperature control in the PID user guide .......)
During brewing, from start to finish, the temperature at the screen and within the coffee puck is not constant. Therefore, technically I don’t think it is 100% correct to use a single number as the ideal brewing temperature. What really counts is the average temperature and time that the grounds are exposed to the water, so I strongly recommend letting brewing results and taste to dictate the set value temperature of the boiler.
As you will find out,
the first cause for the bitter harsh and astringent taste is uneven
too long extraction,
not temperature.
Water pressure delivery: unlike commercial machines, Silvia has no water flow control, no restrictions in water flow and no ability to pre-infuse (pre-soaking the coffee puck before the brew). Therefore in order to achieve the kind of extraction results available from commercial machines, you have to be a little more careful of how you are dosing the portafilter basket (in a home setup you should have the extra time that commercial baristas do not have). However a pre-soaking will not be a magical fix or improvement. In dosing the basket you have two options, dosing and firm tamping or dosing with no tamping or light tamping.
Dosing with tamping (firm tamping):
When you tamp, you are creating a highly compressed coffee puck. As a result any errors in distribution are locked into the pack. The tolerance for any errors in the grind and the tamp is reduced and any chance for error correction through expansion of the coffee or control of the water flow is reduced or lost. Still, if you are able to dose and compress a perfect puck it is like placing a big heavy rock on a glass table. If you can do it without cracking the glass people will consider it a real achievement.
Dosing with NO Tamping or light tamping:
With no tamping ( or soft tamp ) there will be more tolerance for any error in distribution or height of the coffee when dosing the basket. You still have to start with uniform grind distribution, but if you made any errors in height or distribution, the force of the expanding coffee will fill the voids much better than if the coffee has been tamped into a rock hard puck. With no tamping, the puck is soft and is better able to receive or accommodate the pressure from the water above. The heavy rock is less likely to crack the table with a little cushioning underneath it.
Note: If you tamp, you must do it right and know the positive and many possible negative effects. If you are new to espresso or have no good experience with tamping, I strongly recommend you use the no tamping (soft tamping) option. No tamp instruction video coming soon.
For a discussion of the perfect Italian espresso by an industry trade group, see The Instituto Nationale Espresso Italiano (PDF)
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