I got tired of small amounts of froth from yeast cultures bubbling up into the CO2 line and into the tank and making the water cloudy, sometimes a fresh brew bubbles up, sometimes it doesn't, who knows... The oft cited remedy to this problem is to attach a second bottle with a tube in and a tube out so that any froth gets trapped before it gets a chance to head tankwards. The only problem with this solution is that it requires two more seals to be made with the associated possibility of CO2 leakage.

I recently tried putting a (new ) car petrol filter into the line just after the fermentation bottle; you know the ones with the paper element for filtering out crud from the fuel tank of older vehicles. They're completely sealed, seem to be made of polypropylene or something similar so should be CO2-proof and have appropriate attachments for hoses. My CO2 line fitted nice and snug. No more nasty goo entering the tank. Been running for two months now; works great.

How big is your c02 brewing receptacle? I have used a 2.25L coke bottle, and I fill it around half way with the yeast mixture. The mixture never gets anywhere near the top of the bottle.

Ensuring the brewing receptacle is thoroughly sterilized prior to setting it up each time will also ensure no rogue yeast cultures are in the brew.. and it will produce c02 for longer. This may be the reason each of your brews react differently.

Henry

Never though of sterilsing to make it last longer. Unfornutily I have removed my co2 system. Always had the thought that leave a bit in there to help the new batch kick of. But it ever only last a week at a time with rapid drop of.

Will be interested if anybody finds it does make a difference

Mike

That's interesting; I usually just give it a thorough rinse out in hot water before starting a fresh brew. I've been using a 2 litre glass bottle as a fermentation vessel, I might try running it through the dishwasher next time to sterilise it and see if that makes any difference. At the moment, I use two cups of sugar, 1 level teaspoon of yeast and make it up to 1,800mls with warm water. It bubbles away steadily for about 10 days although it could probably go for longer if I let it.

I had thought that the DIY CO2 route would be temporary until I got around to playing with a pressurised system but its really been working so well that I'm hard pushed to see the point of upgrading...

I have read of horror stories on the internet about glass bottles exploding when used for co2 , I'm not sure how true they are however.

I use a 2.25 litre coke bottle filled to the top of the label, with two cups of white sugar, half a teaspoon of yeast and a pinch of baking soda. I get about two weeks out of mine. At the start it runs at about one bubble a second dropping to one every three seconds at the end.

If the outlet from a fermentation bottle were to be completely blocked somehow then I'd say any bottle is in serious danger of exploding as the pressure buildup would be enormous. I use a laboratory schott bottle which is very heavy pyrex glass (I used this as there was a suitable lid available for it with an already sealed outlet for a gas line). But there's nothing between the bottle and the tank to allow any significant buildup of gas pressure and, short of tightly knotting the tubing, I can't imagine how any bottle could build up enough pressure to explode but yes, you do hear the stories...!

Do you think adding baking soda helps to prolong the culture any? Might try that...

The baking soda does nothing - it was believed to counter the low pH in the bottle but it has been found the alcohol kills the yeast long before the pH. Yeast can also survive high extremes in pH (2-8 i think it was).

Cheers

Since I started to include baking soda in the mix however, I have noticed that even a very small pinch of soda seems to completely prevent the sort of frothing that inspired my first post on this topic. Too much (by which I mean about a quarter of a teaspoon or so) seems to hold the brew back and it dies off prematurely but a very small pinch doesn't seem to harm the fermentation process and really does appear to prevent frothing, at least in my hands...