Some brewing questions

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I have some questions that I hope you guys might be able to answer for me...

1) I have a couple of 25L brewing drums and one 30L. If I make up a beer kit to 23 Litres total I notice the bubbling in the air-lock for the 25L drum is usually one bubble at a time but in the 30L drum it seems to build up some pressure and releases a series of bubbles in the one go. Is the extra head room in the 30L causing this?

I also notice that the air-lock can form a water bubble up near the top of the air-lock. This does not seem to cause any problems but it needs enough CO2 pressure to build up before it releases.

2) How much sugar maximum can I add to a Coopers 1.7 Kg kit in a 23 litre brew using the supplied yeast sachet before before the yeast has problems with the alcohol levels?

3) This might be related to the above. I read that adding DAP is a good idea when there is a lot of sugar used to aid in fermentation. Should I be doing that it a Coopers Draught kit brew when 1.5 Kg of white sugar has been used.

4) Is it ok to make a brew of whatever when the total volume is only 4 Litres in a 23 Litres drum. I'm guessing that it would take some extra time for bubbling to commence in the air lock.
Just quickly, have something else to do soon.

1/ An airlock is just a pressure relief device, you can’t rely on it to tell you much about what is going on in the ferment; that is what an Hydrometer is for. Ignore the bubbling and if you keep asking someone will come out with drowning kittens which is an old in house joke.

2/ Could and should are very different questions, add too much and the beer wont taste very good. Given that the upper limit is pretty much controled by the alcohol tollarance of the yeast. Most common dry yeast will go to around 10% ABV (alcohol by volume). We can get a rough estimate of the alcohol by taking the change in gravity and dividing by 7.5. So if a beer started at 1.050 and finished at 1.010 we say it has changed by 40 Points.
40/7.5=5.3%. Given equations work in both directions 10% requires a change of 10*7.5=75 Points. From there we can work out how much sugar you could. I'm not going to do the maths right now, ask if your interested. It comes to just shy of 4kg of sugar (but I wouldn’t do it).

3/ DAP is a source of Nitrogen for yeast and it can help if the wort is low in available Nitrogen. If you aren’t going over 7.5% ABV there should be enough in the can, if you were really pushing the limits alcohol wise some might help. You would be better of using a Yeast Food or Nutrient that contains DAP and a bunch of other stuff.
Bit like using Superphosphate verses really good compost on your garden, guarantee the tomatoes will taste better with the compost...

4/ Well see 1/ forget bubbling.
Not sure if you mean using the kit and a kg of sugar and only adding enough water to make 4L, which won’t work as you would be exceeding the yeasts ability to eat all the sugar. If you mean 4L of normal strength wort no problem.
You are probably right it would take a lot longer to build up enough pressure to make the airlock bubble.

Save yourself a lot of grief, ignore the airlock or as many do just use some gladwrap so the question doesn’t come up!

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