Review + experience in choosing an espresso machine with volumetric dosing control
This article is about Bezzera Duo I bought. Bezzera Matrix is absolutely the same internally, but has plexiglass illuminated side panels with customizable light color (instead of the standard, extremely boring stainless panels in Duo), so I included it in the title to allow this page be found in Google by people who are interested in Matrix as well.
WHAT FEATURES AN ESPRESSO MACHINE MUST HAVE, IMHO
When I was choosing an espresso machine to replace my old Breville Infuser, the following four features were an absolute must:
- PID for temperature constancy control, and the ability to set the temperature (as somebody wrote in FB: "When I try a new coffee and the extraction seems correct but I don't like the taste I play with the temperature"). A visible display should automatically switch to timer when extraction starts.
- The standard 58-mm group, so I can buy a naked portafilter (to control channeling) and a basket larger than 18 gr (to enjoy a bit more liquid using the same brew ratio).
- Volumetric dosing control. Why? Cherchez la femme!
- Pressure gauge. Mostly for control of grind size correctness (in addition to brewing time which is the most important indicator), but also to control the maximum brew pressure - to check the current setting (with a blind basket), and see what I am doing when I am changing it.
- Three way solenoid valve. Allows quick removal of portafilter after espresso extraction by relieving the pressure built up in the grouphead. The result is a dry puck of coffee you can easily knock out of the portafilter.
WHY VOLUMETRIC DOSING CONTROL?
I know, that I will sound not serious, but I bought the Duo for the sake of the volumetric buttons. I am absolutely ok to use a scale to control the brew ratio, but my wife is not. For almost two last years, every morning, before going to work, I was leaving the portafilter with tamped coffee on the countertop. My wife was inserting it to our Breville Infuser, clicking a button - and voalá! According to the found in the Internet, I am not alone in that situation: "with a volumetric machine, once its set up and programmed, anyone in the house can produce a decent coffee without my involvement".
From "The Professional Barista's Handbook":
"It is interesting to note that a barista who pulls shots using a machine's programmable volumetric buttons will achieve a far more consistent espresso brewing ratio than a barista stopping shots by sight. Shots produced with the programmable buttons can vary by volume due to differences in crema quantity, but they will in fact be of reasonably consistent mass."
In addition to increased consistency, volumetric dosing has one more advantage for those who prepare milk-based drinks (as I said, we don't belong to that population, but I provide this info for milk-drinkers): it allows to extract espresso and froth milk in the same time. You can say: ha-ha, any double boiler or HX allows that! Technically - yes, but mentally - no if you want to concentrate on everything you are doing. Both the steps are important, but, at one given moment, you can focus on only one of them (unless you are a of kings of multi-tasking or a many-headed dragon). With volumetric dosing, you can "click-and-forget" a button, and immediately concentrate on steaming. That's what I found:
"The Volumetric option makes your workflow easier in that you can fully focus on your steaming while you are brewing and really not have to watch when to stop the extraction, since it looks after itself. I have a non-DE HX machine, also from Bezzera and I love it, but I never brew and steam at the same time, because I like to be in full control of both the brewing and the steaming and I am just not good at multi-tasking." Another quote from a topic which compares a machine without volumetric dosing with BDB: "no programmable volumetrics; I am not missing it, but I always steam after brewing (not both simultaneously) because I find it hard to focus on two things at the time. ... BDB is programmable, so once you have the correct water volume programmed, you can focus on steaming while the brewing takes care of itself".
Before the Duo, I tried a couple of single-boilers (just to remind, we don't consume milk).
Candidate #1 - Lelit Victoria
The first one was Lelit Victoria. It was my attempt to ignore the "absolute must have" feature #3 - volumetric dosing. :-). I was hoping to convince my wife to use a scale and stop shots manually, but she demonstrated zero enthusiasm, and preferred to keep the existing one-button ceremony. Even the fantastically beautiful appearance didn't help! In addition to that, Victoria's timer counts down from the preset number of seconds (like 25 or 30) to zero - as if I would be launching a space shuttle rather than preparing espresso. It's a terrible solution - you cannot see how many seconds it has taken to achieve the desired brew ratio! You can only see if you guessed or didn't guess with the grind size. :-) Even when I counted seconds by the blinking button (which blinks with the frequency of exactly one blink per second - same as Breville Infuser), Victoria was inconsistent. I did a few shots in a row without changing anything (same coffee, grind size, brew ratio etc.) and with a few minutes between the shots, but the brewing time of each shot was unpredictably different in an unacceptably wide range. All these factors were more than enough to return the Lelit to the store immediately after the weekend, spent to play with it. So, if you want a single boiler of that class with a classical boiler (not thermocoil) and don't need volumetric dosing, I would suggest Quick Mill Silvano Evo instead (BTW, even though it's named a single boiler, you can brew and steam simultaneously since it has a thermoblock and a pump specific to the steaming wand - in the price of a single-boiler!).
Candidate #2 - Ascaso Uno with PID
The second attempt was Ascaso Uno with PID. Same as Breville Infuser, it has a thermocoil (mistakenly named thermoblock, like if it would be a 100-bucks "espresso maker", but they are not the same - google "espresso thermocoil vs thermoblock" for more details). There is no classical boiler with water, which is heated/not heated/heated/not heated all the time - the thermocoil grabs cold water directly from the tank and heats it on demand, each time applying exactly the same amount of heat. That results in unbelievably short warm up time of 1 min 38 sec - I measured the time the boiler needs in the morning to warm up from the room temperature (26 C / 79 F) to 93 C / 199 F. Recovery time (when I was doing shot after shot) was less than the time I needed to grind and tamp the next portion. Ascaso Uno with PID was very consistent. When I produced the same drink weight by the same parameters, I enjoyed the same brewing time plus-minus a second - shot after shot.
But the taste was much less constant, than the "soulless" numeric parameters. Guessing why? Thermocoils have a huge problem which, probably, is the reason why they are not used widely even though their idea is looking super-cool (cheap in production, have very short warm-up time and close to zero recovery time, and you don't keep same water hot in the boiler for weeks). They look ideal, but they are installed literally in a few models among hundreds on market. Have you already guessed what the issue is? OK, here is the answer: brew temperature is flowrate dependent. A slow flowing shot will be hotter, a faster flowing shot will be cooler. Copypase from the Internet: "small flowrate differences will have a rather dramatic effect in temperature. For instance, a shot that flows 10% faster will have a brew temperature that is about 7°c lower. Same goes for faster flowing shots". When you have dialed in, you will have drinks of a same temperature since the water will move through the thermocoil with the same speed, so the heat will be applied during the same time. But, while you are dialing in, and before you have found the correct grind size, water will enter the group having different temperatures. Don't forget, that temperature is one of the factors which affect extraction (and, hence, the grind size)! So, water flow speed affects temperature in the group > temperature in the group affects grind size > grind size affects water flow speed - it's like a snake which bites its own tail (or recursive call, as we, programmers, say). You get unpredictability on top of all the variables espresso hobbyists struggle with. But even after successful dialing in, you don't have full control on the value of temperature. Let's say, you programmed the PID for 93 C. But with which flowrate was it tested by the engineers? An average one? And what about different brew ratios? When it's 1:3, the water is flowing fast and, maybe, doesn't have enough time to get properly hot, while in 1:1.5 brew ratio water is flowing slowly - will it be hot like hell while you see the same number on the display?! In the regular classical boiler, the water will come to the group head with the same temperature regardless the flowrate.
Many times I read, that heat-exchanger machines lack temperature stability. Now I understand what stands after these words. Even though the tube, through which the water flows in HXs, is heated by another hot water (rather than an electrical element), it's the same principle.
I didn't know all that when I was buying the Ascaso (I found that info just after that :-D ) and bought it because it had volumetric dosing. Which... didn't work! Weight of each shot was too different, looking more random than pre-programmed. Soon, I paid attention, that the dosing was programmed by time (even though it's officially called "volumetric"). Unfortunately, that kind of programming doesn't work for me since my habit is to use the time as the indicator of grind size correctness while the brew ratio (i.e. the shot weight) is kept constant. For example, for the same brew ratio, the difference in the taste of a 20 sec and a 35 sec shots will definitely be felt, but it will not be super-drastic (any of these shots will be drinkable even if not ideal), so I have enough room for a mistake in grind size. But if the time pre-programmed, and I get 30 g once, and then 40 gr (absolutely different brew ratios!), the difference in taste will be huge. So, I returned the Ascaso to the store as well.
There were no volumetric single-boilers anymore, so I had no choice but to overpay for the second boiler which will not be used (or, maybe, for steaming coconut or almond milk one day? who knows...).
Candidate #3 - Breville Dual Boiler
Next in line with volumetric control was BDB. It has excellent features, not found in other machines of this price (and even in many much more expensive). But, according to Internet communities, this plastic made-in-China device is more prone to break and has a shorter life expectancy than an average machine. If you explore coffee forums, you will find that this machine is the absolute champion by the number of topics how to fix its issues. In fact, all this upgrade story is happening now because I sold my previous Breville Infuser before troubles would start - it was close to 2 years old. But BDB is still a possible option: even if it will be working less years, its price is very low (taking into account its great features), so, after its extended warranty period (5 years), I could buy another one if it fails. The only problem is that even though BDB can be fixed, I will be forced to replace details (even if Breville will send me them for free). Or, more probably, to bring the machine to a technician since I am not a technical guy - for me, it's not a big deal to create an information system for a financial organization, but I am in a trouble if I need to change a rubber gasket or (oooh, no!!!) to take a screwdriver in my hand.
Candidate #4 (the winner!) - Bezzera Duo DE
The next in line with volumetric control was Bezzera Duo DE priced 3 times higher than BDB (I didn't want much cheaper Bezzera BZ16 DE HX because two the last letters in its name - I have already watched the film "Temp inconsistency"). Duo is built like tank from solid, high-quality metals. That means much lower likelihood of failure and repairs, and longer life expectancy. Yes, full of electronics (which, theoretically, puts the machine in danger), but the technician in the store told me, that there is no reason to be afraid of that: such hightech machines are very reliable, and, according to its multi-years experience, if some part fails in them, it's usually not related to the electronics - it's usually a same mechanic detail as in a non-hightec machine. In addition, Bezzera is famous for the fact that details are produced and easily available even for machines, discontinued many-many years ago.
Let's listen to an owner of a company, which sells espresso equipment: "I am always concerned with the electronics on espresso machines, and this is one reason of several why we do not carry certain brands or certain models of brands at 1st-line. In Bezzera's case, there is proper ventilation holes on the bottom frame and top cup warmer tray to have good airflow. Insulated boilers are good, but improper airflow can cause issues with the electronics." (link).
After all, the BDB (the only existing alternative) is full of electronics too. In other words, if I look over next 15 years, it will be the same money like buying 3 BDBs (roughly, of course, but that is the idea). It's anecdotal, but, in the end of the day, an "expensive" and a "cheap" machines will cost me the same money! But there is a huge difference too: during all those years, I will be enjoying a solid almost-high-end machine of a very respectful Italian company, which specializes in espresso machines (not in blenders and toasters) since 1901. Same dollars, but different feeling. :-) So, I decided to go with Bezzera Duo DE.
Before buying Bezzera Duo DE, I played with its volumetric control in the store. The produced drink weight was incredibly consistent - time after time! In fact, I need the weight consistency (not the volume), so I definitely decided to buy the Duo. At home, I have programmed four the volumetric buttons for different brew ratios - 1:1.67, 1:2, 1:2.5 and 1:3. The first two are for me (I use 1:1.67 or 1:2 depending on beans); the last two are for my wife (1:2.5 or 1:3 - also depending on beans). There is also the 5th button for manual brewing and flash.
In the first few days after programming the buttons, I was still using the scale to control the dosage. The result was more than satisfying: for the same coffee, the weight of shots was different in only 1 or 2 gr most time. In the worst case scenario, the fluctuation was plus/minus 3 gr (especially after switching to other beans). For example, if I programmed 50 gr (the 1:2.5 brew ratio), the actual weight could be 47 or 53 in the worst case. Practically, that means, that the weight, produced by the volumetric buttons each time, is 100% precize. Honestly, I didn't expect that; I would be happy even with less accuracy. So, I absolutely trust the volumetric mechanism, managed by microprocessor, and don't control it with a scale anymore (except of re-programming if new beans require it).
Are you wondering why the produced volume is not the same ALWAYS, regardless grind size and beans type - even in such a serious machine with a computerized flow-meter? That's what the owner of the store, where I bought my Duo, says in a comment to one of his videos:
"The volume remains the same regardless of your grind. However for example if you change your dose this may result in a different volume of brewed coffee. If you increase the amount of coffee or make your grind finer then a larger amount of water is absorbed in the puck. There is no machine that can compensate for this. Anytime you change your coffee we recommend resetting your volumetric doses for the best and most consistent results."
The weight consistency significantly drops if the grind size is ABSOLUTELY incorrect. I experienced that when I just started new beans and had not dialed in yet. So, that is what I do now when I switch to new beans:
- Dial in without volumetric dosing, i.e. in the manual mode (controlling the brew ratio with a scale). I make a shot using the grind size in the middle of my espresso range ("my" - according to my practice rather than marked on the grinder). The brew time (even incorrect yet), gotten for the desired brew ratio, gives me the idea of what the correct grind size should be. Since, in the Neche Zero grinder, one notch roughly represents 5 seconds of extraction, I know how many notches I need to move (and in which direction) to get 26-28 seconds. So, after one or two test shots, a close-to-ideal grind size is found.
- Pull a shot with a volumetric button. Usually, the produced drink weight is correct. Even if it differs in 2-3 gr from the precise weight for the desired brew ratio, I don't re-program the button (that difference will be consistent through all the shots with this coffee, and consistency is more important than an absolutely precize brew ratio - I can live with 1:2.2 instead of 1:2 if it will be 1:2.2 all the way). If the produced drink weight is significantly different, then I re-program the button.
- From now on, I use the volumetric buttons. Even if a further slight correction of grind size is needed (like when the beans are aging), the volumetric mechanism will keep working fine.
[ADDED LATER: After 2.5 months of using the machine, I can say, that I don't use volumetric dosing doing espressos for myself. My wife is happy, I do the programming for her (after all, I am a programmer :-D !), but if you ask about my preference - it's definitely the manual mode.]
The machine is fantastically consistent not least because of its modern electrically heated and specialized "Bezzera group head" ("BGH" :-) ) which guarantees maximum temperature stability thanks to its dedicated heating element. The group heater is dual-chamber to create an even heating surface. It is monitored and controlled by its own PID (the 3rd PID on the machine, in addition to 2 the separate PIDs of each boiler) which ensures that the head remains at the proper temperature at all times. The PID:
- Maintains consistent temperature from one shot to the next.
- Decreases thermal drift (an inconsistency in temperature of water from start to finish of the espresso extraction).
- Ensures that the water, leaving the head into the basket, has exactly the temperature you asked. In many other machines, the actual brew temperature is lower, then the number you see on the screen - you always get a drop no matter how long you warm up the group head. There are machines with an offset programmed into the PID display which is just the best guess at what the brew water will be. Warm up, time between shots, the value of the offset, all affect the final output. If you want to be precise with your brew water, let the machine to manage the temperature in the head rather than guess it!
Attention! The next photo is in 3D! To enjoy the 3D effect, look at it WITH ONE EYE (close another one) from very close distance:
From the Internet:
"The group requires no maintenance; it has no moving parts unlike other machines in the same class that use an E61 group which has mechanical valves and demands regular maintenance or replacement." That's what writes a guy who owned machines with both the groups - BGH (BZ10) and E61: "What I experienced as a downside of the E61 is that I needed to descale the machine after 5 months of use (as thermo heating of the E61 was not working optimal anymore). (Although I was using a scale filter). I only needed to descale the brewing path, not the steam boiler (10 minutes of work). As the brew head of the BZ10 is heated electrically, this problem might occur less frequently. Think the E61 requires a bit more maintenance and technical knowledge from the home barista side."
The next quote is about BZ10 as well:
"I've already had the group head apart, and it is a very simple 1-minute job (three hex screws). I'm not worried about the risk of the electric group head element dying - it looks very easy to replace."
The Duo model with BGH (the one I bought) is named DE ("D" - dosing?). But there is also the MN ("M" - manual?) version - with E61 group and no volumetric buttons. In addition, The same two versions also exist in Bezzera Matrix (so, we have 4 combinations: Duo DE, Duo MN, Matrix DE, Matrix MN - you can see them all on one table in this video). The versions with BGH has an automatic self-washing function (you only need to put a portafilter with a blind basket and a cafiza tablet, and choose the menu option), while the E61 versions require manual washing (the display only gives step-by-step instructions what to do).
I know that many users, which are serious and experienced (in contrast to me), prefere E61 over BGH (that's why the E61 version of Duo/Matrix exist). Maybe, because of a difference in taste ("the bezzera grouphead will produce more clarity in exchange for texture/body. In contrast, the E61 group will have more body (i don't know how much more compared to the bezzera) but slightly less clarity"). Maybe, because of a habit (many years of using E61). Maybe, because of doubts about reliability of all that super-high-end electronics, placed in a hot device (in fact, I have that concern too...). It would be funny if I (a novice) would argue will all these experienced dinosaurs. So, I want to emphasize, that I bought a machine with the "Bezzera group head" since only it had the volumetric buttons. But now I am happy that it's the BGH. I never wanted E61 (that's why I didn't consider Quick Mill Alexia Evo and ECM Classika with PID), and now I am convinced even more than I don't want E61. As my friend, who deals with espresso for decades, says: "You don't want to buy a Chevy 1968 in the era of Tesla!". E61 was unbeatable when PIDs didn't exist. So, if PIDs would not exist today, I would definitely go with E61. Anyway, I don't want to concentrate on that holy war - it can be found in other discussion in the Internet.
GROUP HEAD DEPTH
From the Internet: "BZ machines reportedly have lower head clearance, meaning they don't like updosing". That's true - the shower screen is sitting pretty low. In my 22 gr VST basket, I can put only 17-20 gr of coffee (depending on beans) without tamping too hard and without the coffee tablet touching the shower screen. But the good news is that the 22 gr basket fits the not-naked portafilters which are supplied with the machine. The native basket of Duo is marked as 16 gr - even though it has almost same height as the 22 gr VST.
BTW, that gives us an unexpected benefit: since we cannot fill the basket as fully as with other machines, less coffee grinds will land on your countertop - the basket walls act as a small funnel! Maybe, that was done intentionally?
Another quote from the Internet: "there's less space in the BZ grouphead to trap oil from the coffee that can go rancid and affect the next cup".
USING VST BASKET WITH NAKED PORTAFILTER
Pay attention, that the native Bezzera Duo's NAKED portafilter (sold separately) can house maximum a 20 gr VST basket. If you insert a 22 gr VST basket, it seems to fit perfectly at the first gaze (you can successfully "click" it into the portafilter), but coffee will be spilled on your countertop (after travelling under the beautiful wooden handle) since the holes, which are close to the perimeter, will "look" into inside the portafiler's wall rather than into the large round hole. That happens because the walls of that portafilter are not absolutely vertical all over their height (they go towards the center in their lower part), and VST baskets have the shape of cylinder with a large bottom perimeter - in contrast to regular baskets, which have the shape of cone (with a smaller bottom perimeter). So, if you want to use a 22-24 gr VST basket with a bottomless holder, buy another holder, where the walls don't go towards the center in their lower part.
SWITCH ON / OFF TIMER
The Duo can be programmed to switch on and go to the sleep mode automatically in two ways: 1) the same setting for all the days, or 2) seven different settings for each day of the week. I programmed mine to switch on at 5 AM, so it's ready when I wake up at 6 AM (even 10 minutes would be enough, but sometimes I wake up earlier, than 6 - even at 5). The machine switches off in 9 PM in all days (I usually drink a decaf around 8 PM, so I want to be covered).
HEAT UP TIME
In the morning, when the machine was not on timer (intentionally for this test), it took 3 min 12 sec to warm up the brewing boiler from the room temperature (26 C / 79 F) to 93 C / 199 F. The display signalled that the machine is ready 4 min 2 sec after switch on. At that moment, the group was very hot, but I was still able to touch it. After 2 more minutes, the head became untouchably hot. So, the group is absolutely ready in 6 minutes (which is, I suppose, sooner than E61 or saturated). While you can always put an E61 machine on a timer for the morning, for random drinks during the day the quick warm-up is useful (if you are not going to leave the machine on all day). But, from the other hand, group head warm up time is not very important: even if you suddenly decide to prepare espresso when the machine is cold, and you finish the preparations quicker the full head heat up time, you can heat the group by flashing some hot water through it. That means, that it's absolutely OK to own any espresso machine in a country, where electricity is very expensive, without using the timer.
Recovery time of the Duo is 25 seconds (measured after pulling a 40 gr shot). Did you ever try to do the whole espresso cycle (remove the portafilter, throw the coffee tablet to the knock box, clean the basket, clean the group, weight and grind the coffee, put it in the portafilter, distribute, level, tamp, insert the portafilter to the group and put the cup) in 25 seconds? Some people say it's a disadvantage, that the Duo delivers water from the tank directly to the coffee boiler - in contrast to some other not-HX double boilers (for example, BDB), where the water firstly goes through the steam boiler (kind of lightweight version of heat exchanger), and then enters the brewing boiler having been heated a bit, which decreases recovery time. It's true! If the Duo would work by this schema, the recovery time would be 10 seconds! :-D
Since we don't consume milk-based drinks, I disabled the steam boiler. But if you use it, the machine allows to set which boiler is heated up first after switch on (or during recovery). 3 options exist: the coffee boiler priority; the steam boiler priority; no priority (both the boilers are heated up simultaneously). Since each boiler has its own heating element, I don't understand all these priorities. Will the brewing boiler be heated up slower if the steam boiler is being heated up in the same time?
When the steam boiler is disabled, its temperature is being kept on 33 C (91 F) - no idea why. When you enable it, it takes 7 minutes to bring it to 125 C (257 F). So, if you prepare milk drinks rarely, it makes sense to keep that boiler off, and enable on demand.
Some people think it's a fantastic advantage of Duo. Maybe, it's true for those who have the wife's approval for plumbing tha machine, but I am not among them. As I wrote on FB, "my machine is not plumbed - it's only plumbabale!" :-) Yes, it's more quiet, but the pump noise never was my concern. Some sources say the drink quality is higher because a rotary pump pushes water evenly rather than in waves. This video (which compares two almost identical machines - one with a vibratory pump, another with rotary) says that "the shot from the rotary pump had reacher, deeper flavor and more favorable mouth feel while the vibration pump shot was standard and not nearly that bold", "using the same coffee, grind size, dose and brew temperature, the rotary pump has produce a clearly better shot". I know, that for each given opinion you can easily google the opposite opinion, but I have no choice but believe and hope, that I didn't pay a few extra hundreds bucks for nothing. :-) Anyway, I had no choice since the machine was selected because of satisfying the main condition - volumetric dosing.
My set of torture tools:
Since it's a rotary pump, the pressure is set up on the pump itself rather than on OPV (which is not adjustable and used only for the security purpose). The factory setting is 7 bar. I think, that if the machine would be plumbed, these 7 bar would be added to the tap water pressure, which is something like 3 bars, resulting in the total 10. Since I am a fan of a pressure slightly higher than 9, I increased the default pressure 7, so it fluctuates between 8.5 and 10. 10 is the highest value, shown on the LCD screen even though the OPV opens on 11 - grind too fine and, during the extraction, you will see water, released by the opened OPV, coming to the tray from the same phallic-like detail on the front which discharges water when the three way solenoid valve opens.
Even though the pressure is adjusted from outside, the access is very inconvenient. The regulating screw is underneath the espresso machine, near the rear left leg. It is covered by a black plastic cover, which can be removed with a knife. Fortunately, my countertop has an angle, so I put the machine on that angle, applied the pressure against a blind basket and could see the display while changing the pressure with a flat screwdriver from below. You can see the pressure adjustment of Matrix (same as in Duo) in this video.
Unfortunately, the pre-infusion (PI), programmable up to 5 sec with 0.5 sec steps, works only when the machine is plumbed (the tap water pressure is used as is for wetting), so I don't enjoy pre-infusion anymore. :-) But that has a good side too: now, I am not interested in the holy war "whether or not pre-infusion time is included in the magic 25 seconds"! :-) In fact, lack of pre-infusion is a big problem. If you need volumetric dosing, then it's a hard time deciding between Duo and BDB since BDB not only has PI, but that PI is customizable in a unique way (you can setup PI pressure as a percent of the breing pressure).
Another disadvantage of Bezzera Duo DE when it is not plumbed - the water tank. Firstly, it is filled from the top of the machine (you need to remove the cups warming tray). So, if the machine is standing under an on-wall cabinet, you need to move the very heavy device each time you need to refill. In fact, I found a very narrow and long mug for drinks, and use it to put water without moving the monstrous device - it takes 4-5 times unit the tank is full. Secondly, you cannot see from outside how much water is there (in contrast to Ascaso & BDB). When water comes to the minimum level, the machine suddenly stops working in the middle of a shot, displaying a message asking to refill water! Why not to allow to complete the shot? At that moment, the 450 ml boiler has enough water for many-many more 30/60 ml shots! The water tank is large, 4 liters, but the machine stops working when it still has appr. 1.5 liters, so, in practice, the tank volume is only 2.5 liters (even less since I try to check the water level well before I am in the danger of the message). No idea why the engineers of so good device chose so bad method. It's looking like the machine was born to be plumbed. Unfortunately, I can only dream about that...
I love the Duo. I love my wife. My wife loves the volumetric buttons. But I will be honest with you: I don't recommend it if you don't need volumetric dosing, and you are not going to plumb it. Consider much cheaper options with a modern electrically heated group, PID and more reliable mechanical pressure gauge rather than that super-cool display. If you are ready to spend the money the Duo costs, you can probably find an option where you will pay that money really for something - not for the included smartphone.
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