tonerei said:
Check out some comments Dave made about the Unica he thought the boiler was a bit puny. I thought being small meant it would heat quicker and unless you are pulling shot after shot it would be fine. At the end of the day I have the machine I wanted at a decent price and have no regrets.
A puny boiler won't heat faster (well it will just not significantly -- you're talking a difference of one or two minutes to heat 500ml vs 1000ml). It could affect temperature stability throughout the shot as cold water is pumped into the boiler. Heat up time is largely due to the time it takes to heat the E61 grouphead and portafilter.
Another potential issue with a single boiler which lacks the ability to empty the boiler via a hot water tap (taken from the bottom of the boiler), is that instead you have to empty it through the group (taken half way up the boiler), so when descaling, for example, getting citric acid into the boiler isn't an issue, but getting it out will be a process of dilution (unless you open a fixture at the top of the boiler and syphon it all off). This might not seem like much of an issue at first but if you consider the fact that when you produce steam you leave all of the minerals in the water behind you can see the potential for problems to arise quite easily. With a DB machine you just open the tap and run off some water to refill the tank every now and again depending on how many milk drinks you make to avoid having minerals build up in the boiler which could cause problems beyond your usual scale build up, but with a single boiler set up that isn't a realistic option. Let's say you run it on Volvic to reduce scale or even remineralise your own water to a specific spec you've settled on for taste, and you use it to make two large milky drinks a day, it won't take too long for the extractions to change. Without emptying the boiler the mineral composition that was safe for use in an espresso machine will become saturated with minerals that could potentially cause scale or corrosion, and the mineral composition of the water will be inconsistent from one day to the next until the boiler is completely drained (which would take a lot of flushing as it would again be a process of dilution).
Just to illustrate the point (but I can't be bothered doing the math right now):
Volvic composition:
| pH | 7 (neutral) |
|---|
| Calcium (Ca) | 11.5 |
|---|
| Chloride (Cl) | 13.5 |
|---|
| Bicarbonate (HCO3) | 71 |
|---|
| Magnesium (Mg) | 8 |
|---|
| Nitrate (NO3) | 6.3 |
|---|
| Potassium (K) | 6.2 |
|---|
| Silica (SiO2) | 31.7 |
|---|
| Sodium (Na) | 11.6 |
|---|
Chlorides at 13.5 shouldn't be an issue. La Marzocco say it shouldn't go above 30. Above 20ppm can cause corrosion of brass. I'm not sure but I believe high levels can cause sourness in a brew. I've made my own water with magnesium sulfate and I wouldn't want to go over 30ppm with sulfates because I think I got a weird bitterness from them. I use Calcium chloride now along with Magnesium sulfate to keep the ppm of chlorides below 20ppm and sulfates below 30ppm.
Anyway. When you steam a lot of milk with this and use up 250 ml or more of water you are going to see the minerals climb across the board and to get them out you will have to either run the pump for a long time and waste a lot of water to dilute it down to the point the difference is immeasurable or you're going to have to syphon the water out and replace it. Emptying the boiler half way would be a compromise but minerals will continue to rise assuming continued regular use of steam; this will cause the flavour of your extractions to change, and corrosion and scale could be a concern.
EDIT: BACK TO THE TOPIC
Joysticks. Why? Because I want joysticks. They're cool.