The Solis Crema SL-70s performance overall is what I could consider above average, and I place it on two specific factors: a well tuned and large capacity boiler, and a very unique, yet simple microswitch that greatly improves steaming ability (more on that below). Here's the full scoop, including a battery of test results:
Heating up time
The SL-70 is pretty good in terms of the time it takes to heat up its boiler. I should note that this is just "boiler heat up time". To make the machine properly ready for brewing shots, the entire machine, including grouphead and portafilter all need to be up to "operating temperatures". This can take up to 25 minutes or longer if you do it passively (ie, turn it on, walk away, come back in a half hour), or about 7 minutes if you do it actively (running lots of water through the machine).
In my tests, the machine took an average of one minute and 27 seconds to get to "ready" state, based on five sampled heat up times from a cold (room temperature" machine that had been off at least 4 hours.
Cycling is the term used to describe the action of the boiler automatically turning on, and heating the water during operation of the machine. These times measured reflect a fully heated machine, going into a passive cycle. An active cycle can be forced by running a lot of water through the machine. Passive cycling means you wait for the machine to automatically maintain the boiler pressure while the machine is on, but idle.
The average idle time for the machine is a whopping 14 minutes and 28 seconds.
In my testing, the average machine cycle time was 35:28 seconds/milliseconds, based on five tests: 35:88, 34:82, 35:66, 34:91 and 35:12. This is average. Some machines with much larger boilers can cycle in 20 seconds or less. Some with smaller boilers sometimes take 40 seconds. It's all over the map, and boiler size plays a smaller role than one would think.
I also ran one more test - it was a "volume and time to forced cycle" test. Basically I waited until the machine completed a cycle, and as soon as the ready lamp came on, I ran water through the steam wand, measuring both the time and the volume.
Results: 172ml and 30.7 seconds to forced cycle.
Water temperature tests
One crucial aspect of any espresso machine is how hot it maintains the brewing water during controlled volume tests - or in simpler terms, is it capable of delivering hot enough water to the grouphead for proper espresso extraction. These tests were conducted three times each, and the average temperature for each was calculated. The test was done with a Fluke thermometer and a lead fitted up into the spout of a portafilter, around the filter, and into the basket. Each test was done at the completion of a boiler cycle.
30 ml: 91.9C (Editor's near perfect brewing temperatures)
60 ml: 90.4C (note, getting closer to the edge)
90 ml: 88.8C
180 ml: 85.1C (note, boiler cycled around 170ml, which shows the thermostat has a bit of lag in passing along the proper temps to the onboard heating controller)
The results of these tests are very promising - a single (or double ristretto) is brewed at almost perfect temperatures, a double is very acceptable, and hot water delivery for americanos or tea or hot chocolate up to 175ml or so is very acceptable.
Water flow tests
One area that perhaps doesn't matter as much to a machine's performance but nevertheless does play a small role is the water flow measuring rates. Average should be between 75ml and 100ml in 10 seconds on a domestic espresso machine. The SL-70 scored low in this regard, hitting an average of 62.8ml per 10 seconds unimpeded water flow from the grouphead.
| Aftermarket Filters, first row, pressurized (supplied) filter, second row. Click to enlarge. |
Filter volume measurements
One area that plays a large role in the final shot quality (and also size of the shot) is the amount of coffee grounds the filter baskets can hold at maximum. This is a slightly subjective test - I tried my best to fill the filters with the maximum amount of coffee, tamped normally, then locked into the grouphead, and removed. If I saw dispersion screen indications on the packed puck, I would remove a bit of the grounds, and try again until the puck cleared the grouphead. The packed puck would be knocked out dry onto my 0.1gram measuring scale. I performed this test 3 times with each filter basket, each time using newly ground coffee. Here's the results:
Single Filter (pressurized): 10.8g, 10.6g, 10.6g (Average: 10.7 grams)
Double Filter (pressurized): 13.8g, 13.4g, 13.5g (Average: 13.6grams)
Single Filter (non-pressurized aftermarket): 11.4g, 11.4g, 11.7g (Average: 11.5grams)
Double Filter (non-pressurized aftermarket): 14.9g, 14.7g, 14.5g (Average, 14.7grams)
One would argue that 14 grams is standard; I agree with that. But on my Livia, and on a Rancilio Silvia, and other machines, you can pack in as much as 17 or 18 grams of coffee into a double basket, and the shots are marked improvements with that kind of coffee volume, and also the larger surface area those 58mm filters have over the SL-70's 53mm baskets (and the inside filter area of the unpressurized basket is only 50mm in size).
Other tests and measurements
One other test I did was measuring the temperature of the heating plate up top. I did this with a machine that was on for at least an hour. The measured temperature was 48.7C, not too shabby at all. Maybe a bit warmer would be better, but I can't really complain about this heat.
The measured real volume of the built in reservoir is 3.2 litres average (though the max line is 3.0 litres spot on, you can easily add another 200ml or so).
Other Performance Issues
There are other performance issues about the machine that need some discussion.
One thing I actually like about the SL-70 the design and function of the water reservoir. Because of its design as a separate and external element from the rest of the machine, the reservoir water doesn't get very hot - in fact, it barely nudges above "room temperatures" even with a machine that's been left on all day. In a single boiler machine, this isn't much of an issue this way or that, but I wish more heat exchanger (HE) machines had this kind of design for their reservoirs - one big problem with overall temperature stability (and optimal temperatures) with HE machines is the internal reservoir water heating up to 50, 60 or even 65C. This can cause havoc with the water delivered to the grouphead because it's already hot before it gets to the boiler. Makers of heat exchanger machines should pay a nod to this design by Solis for better ways to minimize heat transfer to reservoirs.
Speaking of boilers, the SL-70's all brass boiler size is claimed at 270cc at capacity. Having seen a Silvia boiler (300cc max) and the SL-70's boiler, 270cc seems a tad high to me, but then again, inside there could be more space in the SL-70 boiler due to design, when compared to the Silvia's boiler. Also, the heating coils in a Silvia boiler take up a lot of space, so that could equal out.
Regardless of all this comparative talk, the Solis' boiler is BIG, and a definite plus for the machine.
Shot performance and recovery time
I found in my usage of the machine that you can squeeze maybe two doubles in one after another, and still get reasonable shots, even the second set. You face a couple of obstacles though. Because the machine does not have a 3 way solenoid, removing the portafilter right after brewing a shot is very tricky, messy, and potentially dangerous - hot grounds will spray all over the place. But if you ease it out very slow, you can minimize the effect. The other obstacle is the colder water you introduced to the boiler from that first shot - the boiler isn't as hot now as it was for the first shot.
So to get ideal shot repetition, the SL-70 is best used right after it cycles, and only one double maximum "per cycle". This means you should do something to force it to cycle the boiler (like run water through the steaming wand to trigger the boiler), and then do your next shot as soon as the boiler cycle ends.
Because of this, the average shot to shot brewing time is about a minute.
As for the shot quality, because of the small basket sizes, the machine suffers in the quality vs volume department. I can get some super tasty rich 45ml (1.5oz) double ristrettos from a Livia or Oscar (or Silvia for that matter) that I simply cannot get from a SL-70. If I tune the volume down to a 28 second, 30ml (1oz) double ristretto with the aftermarket baskets, then I'm getting something super rich.
With regards to performance with the pressurized filters, you might as well forget direct comparisons. You won't get the patented "God shot" from a SL-70 using the pressurized filter baskets, no matter how much you try or finesse it.
This machine has so much going for it that the gimmicky portafilter (no spring, uses a flip latch, spouts built in) along with the stock filter baskets are an even bigger letdown than normal, especially if your pursuit is the perfect espresso shot. Adding the aftermarket baskets makes a difference, and a big one, but the leap cannot overcome the smaller filter size. If the SL-70 had a commercial sized (58mm) standard portafilter, grouphead and filter baskets, it would be a 5 star machine. With the current kit, it's 3.5 stars, and 4 with the aftermarket filters.
The following photos series shows a typical "single ristretto" shot, to the brim of a 45ml ounce shot glass, using the aftermarket double filter basket. These photos are unretouched, but are lighter than the actual colours, because of the strong lighting. Note how the stream really bakes out tan near the end. It took a long time (over a minute) for the crema to fully settle. You can click each photo to enlarge it.
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| Darker in real life! |
| Massive Crema! |
| Go Guinness |
| Go Guinness!! |
| Settling up... |
| Still not settled! |
This is the real star part of this review, and one of the most impressive things about the SL-70. For a single boiler machine, one that relies on the same boiler for brewing water and for steam, it gets up to steaming temperatures very fast - usually 35 seconds or less.
| Steam light is on, meaning the boiler isn't actively heating. Click to enlarge. |
| Steam light is off as soon as you turn the knob. Boiler is heating up! |
But that isn't the best part.
The machine is also a steam demon, getting 210ml (7oz) of milk up to 69C (156F)in an average of 41.2 seconds (based on five tests).
Still, that isn't the best part.
The best part about this machine is something very innovative, but also very simple and one of those "why didn't I think of that" things. That innovative thing is a microswitch attached to the steam knob.
With most other single-boiler machines, you have to "cheat" the boiler to get maximum steaming production. You "cheat" the boiler by tricking the machine to leave the boiler active while you steam. With the Rancilio Silvia, for example, you would get the machine ready for steaming by flipping the steam switch, waiting 20 seconds or so, and bleed the wand of water. You continue doing this off and on for the next 30 seconds or so. When you see the boiler light go off, the machine is up to steaming temperatures, but you open the steam wand again until you see the boiler go active once more. Wait a few seconds, then start steaming while the boiler is still active. You do this because you want the boiler to be actively replacing the steam you're using, by constantly heating the water. It's a tricky thing to pull off, and comes easier with experience.
Guess what. You don't have to do this with the SL-70, and you have that microswitch to thank. As soon as the steaming-ready lamp goes on, as soon as you turn the boiler knob, the microswitch turns on the boiler heating element, to actively produce more steam as long as that knob is turned. Turn the knob off, and the ready lamp goes back on and the boiler heat coil shuts off. Neat stuff, and it makes for a very efficient steaming system that can literally steam for 3 or 4 minutes at near full strength. This system is so easy and cheap to build into a machine that frankly, every single boiler, semi-automatic espresso machine should have it. Most don't, but the SL-70 (and SL-90) do.