Oh dear seems I have left it too long! Started 1st Feb transferred 18th Feb into demijohns rather than fermentor as expected it would take a long time and wanted to see the liquid so without disturbing I could see progress. A constant number of bubbles rising has not really altered since starting. Start s.g. 1.050 transfer s.g. 1.020 on the 3rd April dropped to 1.011 today checked activity still the same so decided not to disturb so s.g. not taken. Kept in dark cool garage temperature does vary between 10 and 16 degs C was sitting at 12.5 degs C this morning. It was done as an experiment to see if lower temperatures (Lagering) improves the taste while this brew has been sitting in garage 4 other brews have been started and bottled and I tasted the so called Lager made the same way as bitter, heavy and mild and that tastes OK so really not sure if all worth while?
However temperature does have a dramatic effect on fermentation and I like many others I am sure rely on the house central heating to keep the temperature up and this does not stay at a steady temperature but varies through the day. Since the beer is such a big heat sink 40 pints takes some warming and cooling the average temperature with a body warmer around the fermentor is around 18 degs C. This is a little on the low side I would like 20 degs C. Start to bottle I expect 3 weeks and I do transfer to secondary ferment into clean fermentor but in real terms this is to reduce sediment not to assist in brewing in fact likely it slows it all down and also damages the brew slightly by adding air during the transfer.
It must also extract gas from the beer as the siphon has to have at least 9 inches between bottom of first fermentor and top of beer is second fermentor as the gas sucked out of the beer by the siphon tube will cause the siphon to fail.
First beer was started Jan 2013 by my wife and was left in the fermentor until March at which time I took over and bottled it. No s.g. was measured. No air lock used just a bung in the hole which did not seal very well. The beer tasted great which started my home brewing. Now I use a very well sealed air lock using an electrical stuffing gland and measure the s.g. but in real terms this just means I can bottle quicker as I now know when the fermentation is complete.
I believe the air lock if well sealed stops bacteria getting into the beer not because it would get through small leaks but because I use the air lock to show me when complete so don't need to remove the lid. The s.g. is taken to confirm fermentation is complete but air lock bubbles are used to show without removing lid when it has likely reached this stage.
The stick on temperature strips are also an essential guide to know if reduction in bubbles is due to finished fermentation or beer too cool.
But to my mind the air lock, hydrometer, and temperature strip are only required when one is in a hurry to start next brew. I did have one brew which caused a problem. Coopers Ginger Beer all three attempts at this kit required extra yeast adding and also very much longer time than instructions stated. All other kits I have used if double the time stated is given the brew is complete assuming you have not added extra sugar or made some other alteration to the kit.
Once one leaves the kit and start doing it all yes there is need for a lot more control but in the main full DIY costs more than using a simple kit and is for the true enthusiast not simply a way to make cheap beer. It also required a lot more space so for me it is simple kit. £7 for kit plus sugar from Morrisons means 20p a pint that's why I home brew yes will do experiments but in the main just cheap beer.
As to experiments the transferring to secondary ferment can be into 6 demijohns which allows things to be added to just 6/7 pints rather then whole lot. Messing up 40 pints is one thing but messing up 7 pints is worth the chance. However a demijohn will vary in temperature faster than 40 pints in a fermentor and takes up more room. Where siphon has been lost near the end of transfer and remaining has been poured into a demijohn the beer in demijohn is ready to bottle quicker than main brew.
As to if this is temperature or the amount of yeast I don't know.
If I was to go on holiday then I would also turn off central heating so beer would take longer.