homebrewandbeer.com

I notice that the lower end of the temperature scale is recommended by all, however a lower temperature equals a much longer fermentation period with a much greater chance of infection. I have actually seen a recommendation for a brewing temperature of 9 deg for lagers (using Saflager yeast). As brewing a lager even at 19 deg takes about 2 weeks, how long would it take at 9 deg resulting in a potentially greater chance of infection?

as long as you are sanitary in your methods you shouldn't have a problem

people usually pitch the yeast at higher temps say at 15 degrees for lagers and then drop the temp to make sure that the yeast gets a good hold on the brew preventing any undesirables taking over

further as the fermentation goes along there are less and less fermentable to sustain the infections

cheers

The risk of infection is only really present when the fermenter is open. Once it's all sealed, there should be no way for nasties to get in. If they're already in there then you're screwed whether you brew at a high temperature or a low temperature.

You're right that once closed no new nasties can get in, but it's still possible that a slow fermentation could be more infection prone.

In a "normal" fermentation, the yeast quickly multiplies and eats up the fermentable sugars over a period of about a week. Most yeasts have a generation time of about 20 minutes (i.e. when in dividing mode, they divide about every 20 minutes). If one of the bugs that floated in on the air while the fermenter was open had a generation time of 1 hour, then it won't be able to compete because the sugars are all gone before its population gets to any appreciable level. However in a cold fermentation, the yeast will divide more slowly and consume the sugars more slowly, so if the stray bug is less temperature sensitive than the yeast, it'll get a gurnsey and properly infect your brew.

Fortunately, this doesn't seem to be too much of a problem in practice.

FWIW, consider a brew where you put in half ale yeast and half lager yeast. Which flavour profile would dominate? Well, it'd depend partly on the temperature. If you fermented it at 10degC, the ale yeast would be mostly dormant and the lager yeast profile would dominate. If you fermented it at 20degC, then the ale yeast would be much more vigorous so you'd get more ale character.

Tom

i brewed a lager a while ago using saflager yeast and brewing at 11 degrees andit only took 10 days to ferment and it is now a really good beer

Ive had a Morgans pilsner in the primary for 4 weeks now @ 10-12c its going to be a beauty. Its nice and clear and smells great going to bottle this weekend. this is the second one Ive done this way with no problems.
:) Cheers Bill

Ive brewed all my lagers this winter at between 9-12*C and have not had any problems, admitidly some of them took up to three weeks to ferment out, as long as you have active fermentation there is no real risk of infection, as far as i know the most critical stage is gettin the yeast started fermenting as quickly as possible ie: making a liquid starter or rehydrating dried yeast, but once fermentation is present there should be little to no risk of infection

Perhaps an increased risk of infection occurs when the fermentor top is unscrewed and the hydrometer is used to test whether fermentation has finished. This may be required to be repeated a few times before its ready to bottle as you cannot always rely on observing bubbles in the air lock to determine whether fermentation is complete. I would think that the longer the brewing time, the more tests resulting in greater chances of infection. Maybe this can be overcome by care and experience.

gaggymoon wrote:Perhaps an increased risk of infection occurs when the fermentor top is unscrewed and the hydrometer is used to test whether fermentation has finished. This may be required to be repeated a few times before its ready to bottle as you cannot always rely on observing bubbles in the air lock to determine whether fermentation is complete. I would think that the longer the brewing time, the more tests resulting in greater chances of infection. Maybe this can be overcome by care and experience.

Use the test tube provided with the hydrometer, pour some in it out of the tap and your possible infection problem is solved, after all thats what the tube is for

Unfortunately, you still have to unscrew the fermentor top as unless you do, the water in the air lock is sucked into the brew when you turn on the tap at the fermentor bottom.

you only need to crack the seal not unscrew it fully, in doing this there is vertually zero chance of infection as it would be mighty hard for them to get in under the lid in the 5 seconds it takes to collect a sample

gaggymoon wrote:Unfortunately, you still have to unscrew the fermentor top as unless you do, the water in the air lock is sucked into the brew when you turn on the tap at the fermentor bottom.

I find that if I only fill to the mark on my airlock, it does not suck into brew. IE use minimum water in airlock.

My mate used to fill his airlock right up, but his used to get infection a couple of days after testing

if you open the tap slowly and watch the airlock you can see when it is getting close. An easier way is to simply remove the airlock rather than the lid as this is a smaller hole. Dont do what i did and forget about the airlock on my first couple of brews. When bottling sucked back through the airlock. Doh.

Good thinking Morgs, I also have forgotten to unscrew the lid when bottling. Simply removing the airlock when testing and bottling is the way to go!