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Hop flavour gone after 1 day in keg

Discussion in 'Gear and Equipment' started by brewermp, 10/7/19.

 

  1. MHB

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    Posted 17/7/19
    Not so sure about Ascorbic Acid, not sure its aggressive enough to ensure that all the O2 would be scrubbed out on the way through. It is used as a component in some industrial O2 absorbers, usually with a catalyst, and I get the impression its fairly slow. Used in some of the little sachets that you find in flat bread and the like, also incorporated into polymer films on the inside of packaging
    Tap water brings it s own O2, in fact municipal water is usually aerated as part of its treatment, so boiled water would be a better choice than tap water.
    Metabisulphite at low pH isn't in the free SO2 form but in the SO3- form that we want for O2 absorption.
    In the following which shows the various species, where it says the SO3 form is irrelevant, its talking about the effect on preserving wine. Beer is mostly in the 4-4.3pH range (at packaging) so over the pH where you start getting free SO2.
    Without more evidence I'm sticking to High pH Metabisulphite, cheap enough, easy to do and I'm sure its very effective.
    If I were to use a keg in line I think putting an air-stone on the end of the dip-tube would be a very good idea.
    Mark
    upload_2019-7-17_10-26-13.png
     
  2. Tangle Foot

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    Posted 19/7/19
    Hi Mark,

    Think I will set up a keg with the scrubbing solution you mentioned. A couple of questions come to mind.

    1. Due to space limitations in my beer fridge, I thought that I would put the scrubbing keg outside my fridge with the gas bottle in line. Connection would be gas bottle -> scrubbing keg -> through fridge wall -> CO2 manifold -> serving kegs. Does that all seem OK? Is the scrubbing solution likely to be as effective at 20 deg C ambient as at fridge temperature?

    2. How long would the scrubbing solution be effective for? Does it function like a buffer solution and thus lose effectiveness as it does the job? Should I replace it every time I put in a new serving keg (once a month for me)? Or maybe every time I replace a gas bottle (once a year)? Or something in between?

    Appreciate your thoughts.

    Cheers
    Alex
     
  3. MHB

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    Posted 20/7/19
    I would put it outside the fridge, most chemical reactions happen faster warmer which is what we want to encourage.
    That said it is a chemical reaction so the scrubber is used up, question is how fast. Looking at the specifications for CO2 in Australia they mostly say its better than 99.99% CO2, the balance is basically air which is roughly 20% Oxygen.
    So 1kg of CO2 would have at most 0.1g of other gases of which 20% may be O2 so 0.02g.
    Short answer is that a keg say 3/4 full of scrubbing solution would be more than enough to clean up a whole 6kg bottle of CO2, IF it was 100% efficient. Fitting an air-stone to the bottom of the dip tube (one of those carbonator lids would be good to) will make the reaction more likely, slow gas flow rates will be better (normal use) but high flows might let some gas through untreated...
    I cant give you a definite answer on how often to change the scrubber, use it carefully (avoid really fast flows of gas)
    0.1M sodium carbonate comes to about 10g/L (10.59 if it matters) and about 250ppm of Sodium Metabisulphite is 0.25g/L would be a good minimum, I'd probably double that.
    Hope that helps, be interesting to see how it works

    Any with access to a really good DO meter? if so I would be happy to supply all the bits and pieces so we can measure the outcomes.
    Mark

    PS when you buy Sodium Carbonate - watch the hydration, that will change the amount you need.
    M
     
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  4. 2095brewer

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    Posted 20/7/19
    Goatchop...

    All that (very theoretical) work from low oxygen brewing doesn’t recognise the fact that the higher mass and lower temp of CO2 used to purge a keg will make it sink towards the bottom of the keg, no? So when you release via the gas pressure relief valve it will come from the top, hence be higher O2 content. I recognise it is not perfect, but returns aren’t as diminished as they quote in their huge document.

    I’m definitely one for ways to improve, but I’d like to see something with some proof rather than hypothetical theories. Love the creative and lateral thinking, but does anyone from a commercial setup that might have some good evidence based advice for us home brewers?

    Thanks.
     
  5. peteru

    Here, taste this!

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    Posted 21/7/19
    No. That is a common misconception. First, you have turbulence and mixing of gasses, then there's diffusion.

    You don't end up with a cylinder full of pure CO2 with a thin layer of O2 on top when you let it stand.
     
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  6. Coalminer

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    Posted 21/7/19
    If it did we would all be dead
     
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  7. 2095brewer

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    Posted 22/7/19
    No, we aren’t dead because nobody goes and locally releases mass amounts of cold CO2 above you. I’m not suggesting everything in the atmosphere breaks down from it’s % or composition and falls out and layers IAW it’s molecular mass. If you’re near a massive sinkhole/volcanic vent releasing CO2 you probably would die. Quite a few people have. It doesn’t magically instantly mix on release with the total volume of earths atmosphere. It will eventually, I get that. I also didn’t suggest pure CO2 remains by letting it stand to form layers. Your words. I just suggested that complete mixing (as demonstrated by their graph) isn’t a realistic or real outcome.

    So in high local concentrations, short bursts and time frames where it hasn’t had time to warm to ambient temps, or diffuse, you’re saying that it just magically warms and or fully mixes? Why do they bother CO2 purging cans with this method in commercial canning. Are they wasting their time and don’t know what they’re doing? It’s kind of the same philosophy, no?
     
    Last edited: 22/7/19

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