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Random malt debris blockage in mash tun manifold

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  • Random malt debris blockage in mash tun manifold

    We have a 20 bbl two-vessel system (mash/lauter + kettle/whirlpool). We make a hearty brown ale with about 10% flaked rye in the mash. We have been finding over the last 6 months that occasionally, fairly exclusively to this beer, one of the ports below the screen will get plugged up with malt debris reducing our efficiency (we usually yield about 25% less wort when this happens). The manifold from the tun has four 1" ports that feed into a 1/5" header into the mash pump into the kettle.

    Very often we will double or triple batch and we are more likely to have this happen on the second or third batch of the run, but not necessarily. Brewers are careful to rinse underneath the mash tun and flush out debris between runs. We have tried adding rice hulls to the mash tun before adding the rye which seems to have slightly improved our failure rate but has not eliminated it altogether. We will mash out this beer since we are going for something fairly medium-full bodied and trying to preserve attenuation profile. During mash out we usually have to spin with our rake at a pretty fast speed to keep temperature uniform, we theorized that we might be grinding malt (or rye) dust into the screen during this mash out process. We have other beers we make via a very similar process with no issues, so I assume it's the rye. This issue happens maybe every 3-5 batches.

    Any ideas of how to improve or eliminate this? Thanks.

  • #2
    I don't understand why you are using the rake to mix up the bed. Why do you consider the temperature is inconsistent and consider it essential to stir it all up?

    The use of rakes is destroying the bed structure and unless you allow to resettle before running off, will be using the false floor as a filter, not the grain bed itself. The grain bed is the filter for bright wort, and no amount of husk of any sort will create a filter bed whilst you are stirring.

    A 1.5 inch header should be fine for the runoff flow rates, though if the header is virtually horizontal, the heavier grain particles will rapidly clog up the pipes as the flow through individual pipes is far too slow to keep in suspension (guesstimate of flow rate through each runoff pipe of < 0.3 metres / second where good turbulent flow to keep particles in suspension will be closer to 2 metres / sec), so you need to allow the bed to settle properly before vorlaufing then running off if you really have to stir the bed up.
    dick

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    • #3
      Originally posted by dick murton View Post
      I don't understand why you are using the rake to mix up the bed. Why do you consider the temperature is inconsistent and consider it essential to stir it all up?

      The use of rakes is destroying the bed structure and unless you allow to resettle before running off, will be using the false floor as a filter, not the grain bed itself. The grain bed is the filter for bright wort, and no amount of husk of any sort will create a filter bed whilst you are stirring.

      A 1.5 inch header should be fine for the runoff flow rates, though if the header is virtually horizontal, the heavier grain particles will rapidly clog up the pipes as the flow through individual pipes is far too slow to keep in suspension (guesstimate of flow rate through each runoff pipe of < 0.3 metres / second where good turbulent flow to keep particles in suspension will be closer to 2 metres / sec), so you need to allow the bed to settle properly before vorlaufing then running off if you really have to stir the bed up.
      We mash at one temp, then mash out at another - the steam jacket is along the walls and the mash requires stirring to allow the entire bed to come up to temperature. We will reset and rest the bed and re-vorlauf before transferring to the kettle. Although, this second voraluf is only 15 mins long. We don't transfer while the mash is stirring. I'm more worried that stirring the mash is sending too many particles below the screen. Are you suggesting we wait longer between the completion of reaching mashout temp and initiating the vorlauf to allow the bed to rest?

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      • #4
        OK, So I understand why you mix, if wanting to raise the mash temperature.

        Using the rakes will knock the air out of the mash, forming a much more impervious bed that sits on the false floor of the MT. I assume you use the rakes during initial mashing in, and then have to assume that you don't have this runoff pipe blockage problem with other beers. I am also assuming from your comments / lack of, that you don't normally raise the mash temperature of other beers just before runoff. Why not try simply raising the mashing in temperature half a degree or perhaps a full degree C (1 or 2 deg F) and then runoff without addition temperature rise with stirring? At the extreme, I have brewed low alcohol beers (ca 1%) using very mash temperatures (circa 80 C) in mash tuns without rakes, so temperature control of the mash in (and time) is easy to alter the fermentability.

        You are trying to carry out the two separate functions in the same vessel that are carried out more commonly in two separate vessels - a mash mixer, with heating surfaces and mixing paddle, and a separate lauter tun with speed and height controlled rakes. Unfortunately, trying to combine the two in a single vessel simply doesn't work as well as two separate vessels.

        If you want to clean out the pipes, it will take a bit of welding, but backflush through the individual runoff pipes into the tun, by putting isolation valves in the individual runoff pipes, and then running the flush liquor and debris out drain - flushing out each one in turn - a minutes process for each pipe, followed by a flush by the sparge system (to get even flush across the false and true floors) to drain to flush out any resettled debris.

        For simplicity, I would simply raise the mash in temperature and not raise the pre-runoff temperature as a first attempt at a solution.
        dick

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