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Breville BES870 - Over extraction only on second shot

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  • Breville BES870 - Over extraction only on second shot

    Hi all,

    I am having a very interesting issue with my BES870. I normally would wake up to make myself a coffee with this machine and everything was fine. I can consistently make a coffee with pressure indicating the sweat spot range.

    However, whenever the missus would like a cuppa, i would then proceed to dump the used grounds and restart the coffee making process. This is when i always get the pressure wayyyyyy to high (over extraction).

    This is really strange for me and i cant figure out what i did wrong. Note that if i made a cup of coffee in the morning with success, and come back home in the evening for another cup, all would be good. The issue only arises when i am trying to make 2 consecutive cups of coffee.

    Now the funny thing is, i have done everything as consistent as the first cup i made, but would consistently fail on the immediate second cup. Things to note:

    1) beans are fresh and grind with same coarseness settings (Number 4 settings)
    2) amount of beans settings have been left the same between cup 1 and cup 2
    3) temper pressure is kept as close to identical as i can (Note this can be subjective, but if the inconsistency in temping pressure is the issue, why is it always the immediate second cup that fails?)
    4) i DO NOT reuse the beans from the first cup.
    5) after extraction of the first shot, i would dump the used ground beans, take out the portafilter and the basket for a quick rinse, before grounding new coffee beans for the next cup.

    Lastly, i did notice that there is a word "lock" just under the grouphead which is suppose to aligned with the portafilter handle when the portafilter is lock against the grouphead. However, if i overturn the handle where it would exceed the alignment against the word lock, i am likely to get an over extraction. I suspect this is because the ground beans within the porta filter is pushed up against the grouphead too much and further compacting the beans within causing pressure to rise.

    Now when i make my first and second coffee, i try my best to align the handle against the word "lock"on the grouphead. It seems to not work. On the second cup, i might want to try easing it about just 1cm off from the word "lock" and seem to have minor success (not consistent).

    Can anyone shed some light on my issue? Thanks so much in advance.

    Cheers!

  • #2
    It sounds to me that the water temperature is unstable and ends up being much higher than the first when extracting the second cup.

    Comment


    • #3
      First lot of beans ground are stale from sitting in the grinder overnight maybe. Try grinding a basket full. Chucking them out. Then grinding again. May find you choke it and will need to readjust the grind and learn to purge the grinder first thing in the morning.
      Last edited by Lukemc; 22 October 2016, 04:31 PM.

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      • #4
        Have you weighed each dose to ensure they are the same? You might be getting a low dose first up if you are tipping the beans in fresh each morning.

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        • #5
          Thanks for all the responses.

          Toorakwa - I am unsure if the unstable temperature would affect the pressure? my understanding is that the pressure is a function of volume of hot water going through the portafiler and the "compactness" of the ground beans, which is also a function of the amount of beans.

          As for the beans in the grinder, i typically would have enough beans in the basket overnight, so i am not refilling or tipping in fresh beans each morning. I typically would buy 120g bag of beans and tip in half a bag until i finish them.


          cool some of you guys are from Perth!!

          Comment


          • #6
            Originally posted by ViceVersa View Post
            Toorakwa - I am unsure if the unstable temperature would affect the pressure? my understanding is that the pressure is a function of volume of hot water going through the portafiler and the "compactness" of the ground beans, which is also a function of the amount of beans.
            Technically, an increase in temperature results in an increase in pressure (ever put a tin of baked beans on a campfire when you were young and/or reckless?). According to the combined gas law (https://en.wikipedia.org/wiki/Combined_gas_law) the assumption is that the volume (V) should be the same with your first & second shots, which is the area of the voids between the ground coffee particles in the basket assuming that the tamp-height is the same. Therefore you can assume that there is no change in volume, and accordingly a difference in temperature would be directly proportional to an increase in pressure.


            Originally posted by ViceVersa View Post
            As for the beans in the grinder, i typically would have enough beans in the basket overnight, so i am not refilling or tipping in fresh beans each morning. I typically would buy 120g bag of beans and tip in half a bag until i finish them.
            This may be more to do with the problem than a change in temperature. As the oils in coffee are highly reactive beans left in a hopper are exposed to air and will oxidise rapidly (we're talking minutes here, not hours or days!). The advice in general is to only grind beans as required and otherwise leave them in an airtight container with a one-way valve to allow them to degas. I don't have any experience with grinding/extracting from highly-oxidised beans however I'd say that the particle characteristics might be a lot different. Going back to the combined gas law concept, if temperature is stable then the volume must have become reduced to result in higher pressure - this would indicate that even if you tamp at the same level, the oxidised beans would have a lower amount of voids between particles.

            Saying that, if you're using oxidised beans for both first & second shots there could be another factor in play, In any case, my advice would be to store the beans in the bag they came in (as long as it's a sealable bag with a one-way valve, otherwise get some of these: CoffeeSnobs - BeanBay - Other Stuff - 250g Stand-up Valve Bags - SPECIAL) and only put fresh beans in the hopper as required for grinding. If you give that a go let us know if it makes any difference!

            Comment


            • #7
              Hi CoffeeHack,

              Thanks so much for the detailed response. Silly me, i agree with the temperature affecting the pressure now that you have explained it well.

              With regards to the beans, both shot 1 and shot 2 are grind from beans stored in the coffee grinder basket. Hence the inconsistency in pressure from shot 1 and shot 2 seem to be not due to where the beans are stored.

              I am starting to think if the temperature is the problem. But strange that my mate and I have the same machine and he had no issue such as mine...

              Cheers.

              Comment


              • #8
                To be honest I doubt that the change in temperature would be great enough to make such a difference between shots. Consistency from machine to machine can be variable, even in high-end equipment - you'll see on some of the sponsors' websites that they will specifically calibrate the prosumer machines they sell as each machine can have subtle differences not only with the major machine components but also in-built sensors & gauges. Many snobbers on here would say the differences between consumer (Breville/Sunbeam) machines could be a lot different.

                Have you tried contacting Breville customer support? They will probably suggest a similar troubleshooting process as discussed by everyone on this thread, however they could be aware of this being a common problem and have a suggested fix. Good luck!

                Comment


                • #9
                  Another thing I just thought of is that the portafiller handle temperature could also be affecting the temperature. If you don't pre-warm the portafiller & basket with hot water, then once the extraction starts the metal of the handle will absorb some of the water temperature and affect the water passing through the coffee grounds. The second shot will be with a much hotter portafiller which could then be a factor...

                  Comment


                  • #10
                    Originally posted by Lukemc View Post
                    First lot of beans ground are stale from sitting in the grinder overnight maybe. Try grinding a basket full. Chucking them out. Then grinding again. May find you choke it and will need to readjust the grind and learn to purge the grinder first thing in the morning.
                    As above Try purging the first lot of ground beans jnto the bin then use the second one as your first shot of the morning. I reckon it will choke and you can grind courser from then on but will always need a purge.

                    I really think the issue is being overthought. Your grinder will be retaining stale ground coffee overnight. Not the beans. But actual ground coffee that's sitting in the throat of the grinder that is pushed out when you start grinding again.

                    If I'm wrong I'm wrong but it's an test to do and eliminate one possible issue. Temp etc is a lot harder.

                    Comment


                    • #11
                      Are you cleaning the screen in the group head between shots? You can do this by pressing the one or two cup button without the portafilter in (or in but with no coffee). I also have a bes870 and have noticed even when dosing correctly, a lot of grounds can be left on the screen and can play havoc with your next shot. The issue may be less prominent on the first shot as the grounds would have dried/dispersed since last use.

                      Some other tips I have found useful with this machine (some already mentioned)

                      Avoid storing beans in the hopper (weigh out dose for each shot)
                      Grind 15-20gm of fresh beans to flush the grinder of stale grounds
                      Run a shot or two through the portafilter to warm up before use
                      Run a empty shot between each espresso shot to clean the group head screen
                      It also says it has an auto purge function, but I think this is only for temperature purposes. I like to purge the steam wand after use as there is usually milk left in there.

                      Comment


                      • #12
                        Last week I was playing around with a thermocouple placed inside the portafilter and charting the results, just for interests sake. I can tell you with certainty in my machine at least, the second shot issignificantly hotter than the first, and the third is a little hotter again - and about right. From what I've seen, the first shot should go down the sink (empty basket of course). For whatever reason it is, the lines, shower screen, and portafilter coming up to temperature or bubbles or whatever, the first shot barely reaches 80ºC. Successive shots are in the butter zone of 90-95ºC. Whether or not it is causing your issue I don't know, but I'd say running a shot or two before starting is good practice anyway. I always run a shot for 3-4 seconds after brewing to clean the shower screen too. Never had the issue you are describing!

                        Good luck anyhow!
                        Josh

                        Comment


                        • #13
                          Temperature Instability is a major problem I've experienced with this machine. I've run some tests. Basically, pulling a blank shot of water into a pre-warmed cup and measuring with a digital thermometer at the end of the extraction. These are my results on the default temp setting (93 degrees).

                          2mins: 76deg
                          3mins: 80deg
                          6mins: 79deg
                          7mins: 82deg
                          10mins: 78deg
                          11mins: 83deg
                          14mins: 82deg
                          15mins: 83deg
                          18mins: 79deg
                          19mins: 83deg
                          20mins 84deg
                          28mins: 79deg
                          29mins: 81deg
                          39mins: 85deg
                          41mins: 79deg
                          42mins: 85deg

                          So as you can see there are some wild fluctuations in temperature reported here which can affect the espresso shot. For a 30sec extraction, the yield can vary quite a bit depending on the temperature. I've tested this. A 30sec shot with a 20g dose at the hottest temperature setting might come out at 38ml. For the coolest temperature, you may get 54ml. Different beans give different results but there's a pattern here.

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                          • #14
                            Hello
                            did you get to the bottom of this issue, I have the same experience.

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