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Thread: Fobber or Pre-Evac?

  1. #1
    Join Date
    Nov 2003
    United States

    Fobber or Pre-Evac?

    We have a small 2 head in-line filler. We've added a liquid ring evac pump with a stainless canister. Which has worked great, no oxidization. But we need a much bigger bottler to keep up with demand. While shopping for this I've noticed most of the rotary machines around 24 valve size don't have pre evacuation. I've heard a little about ones with a fobber. Is pre evac essential or is a fobber enough? Should we consider retro fitting a pre evac? What's the difference? liquid Nit. seems pricey.

  2. #2
    Join Date
    Oct 2002
    Tadcaster, Yorkshire, UK
    Unfortunately, for best shelf life, you really will benefit from having both systems.

    Pre evacuation removes much of the oxygen from the bottle (or can - to a much lesser extent due to the low strength of cans). As a result, when the bottle is repressurised with CO2, the level of oxygen in the gas in the bottle is greatly reduced. Modern high speed fillers by suppliers such as Krones or SIG actually repeat this for maximum benefit (double evacuation fillers).

    So we now reduce the amount of oxygen entrained in the bottle (or can) so increasing the shelf life (assuming decent microbiological and haze material removal during cold storage and filtration) allowing longer shelf life.

    During filling, we should aim to have minimal foam production in the bottle immediately after filling and release of excess pressure, (there should be minimal fob left in the bottle neck above the beer). The problem then is that this head space will then allow replacement of CO2 immediately above the beer, with air (oxygen) between the filler discharge and the crowner, reducing the shelf life due to oxidation. If we use a bottle tapper, or more realistically a jetter mechanism (fobber) we cause the beer to foam up and replace the air / CO2 headspace with fob from the beer, which definitely contains CO2, not air. Thus a fobber is essential to remove air in headspace. The headspace should be filled with fob just prior to fitting the crown to the bottle. In order to achieve a decent fob to fill the bottle neck, the beer CO2 level needs to be reasonably high, say 2 v/v minimum, in some ways the higher the CO2 content, the easier it is to generate suitable neck foam.

    If I had the choice of only one, if I was using a long tube filler, I would go for the fobber. I think, but am not totally sure, if I was using a short tube filler, I would go for pre-evacuation - but am happy to be swayed by others opinions. Actually If I was using a long tube filler, I would try and sort out some sort of tapper mechanism or jetter, as I believe both are required, even if filling for a bottle conditioned beer

    Hope this helps


  3. #3
    Join Date
    Feb 2004
    Pre-evacuation adds extra cost and complexity to fillers (vacuum pumps, more complex filling valves, etc.). That is why it is usually reserved for larger fillers.

    Fobbing is done on both pre-evac and non pre-evac fillers to reduce headspace air levels. This is often done with a very fine jet of sterile water. Years back, bottles were mechanically thumped to induce foaming.

    I have worked with smaller long tube fillers without pre-evac and run relatively low airs (<.5 ml). Pre-evac machines can cut this number in half if they are properly run.

    Liquid N2 dosing can reduce oxygen levels in headspace. It can be expensive to run and you would require some pricey lab equipment to check headspace oxygen levels (thousands of dollars). Without N2 you 'just' need a Zahm package CO2/ air checker ($1000 or so).

    Good Luck,

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