Fermentation slowing down, then speeding up?

I'm making a high gravity belgian ale. This recipe called for a pound of sugar and said the fermentation would take 3-4 weeks.

I'm used to an ale that stops bubbling in 3-5 days and then I wait a few days after that before bottling.

I understand this will take a while but what's interesting is the bubbles from the air gap slowed down to about once every 12-13 seconds at around 4 days, but today, at day 8, is every 4 seconds or so. I haven't done anything different so what would cause it to speed up?

Also, I was planning a secondary fermentation on this batch. When should I do that? after bubbles stop or after two weeks?

You mean your airlock is speeding up and slowing down, right? That's not the same thing as your fermentation slowing down and speeding up. Your airlock is a valve, a vent to release excess co2m it's not a magic fermentation gauge. There's various reasons why the rate of gas will change coming out of your airlock that has nothing to do with fermentation. Like a change in temp, or the cat nudging the fermenter.

Airlock bubbling and fermentation are not the same things, so a slowing airlock doesn't equate with slowing fermentation, or really anything....

Airlock activity is irrevelent. Just gravity points on a hydrometer. And yes bubbling slows down eventually.

Airlock bubbling (or lack) and fermentation are not the same thing. You have to separate that from your mindset. Airlock bubbling can be a sign of fermentation, but not a good one, because the airlock will often blip or not blip for various other reasons...so it is a tenuous connection at best.

If your airlock was bubbling and stopped---It doesn't mean fermentation has stopped.

If you airlock isn't bubbling, it doesn't mean your fermentation hasn't started....

If your airlock starts bubbling, it really doesn't matter.

If your airlock NEVER bubbles, it doesn't mean anything is wrong or right.

Your airlock is not a fermentation gauge, it is a VALVE to release excess co2. If it bubbles it is because it needs to, if it doesn't, it just means it doesn't need too...


Your HYDROMETER is the only BEST indicator of fermentation activity. Nothing else is accurate or consistent...

Unless you take a gravity reading you don't know what's really going on, not by airlock bubbling or by krausen formation. Neither of those signs are effective, they don't tell you exactly where on the fermentation process you are.

Fermentation is not always "dynamic," just because you don't SEE anything happening, doesn't mean that any-thing's wrong,, and also doesn't mean that the yeast are still not working diligently away, doing what they've been doing for over 4,000 years.

That's why you need to take a gravity reading to know how your fermentation is going, NOT go by airlocks, or size of krausen, or a calendar, the horoscope or the phases of the moon (those things in my mind are equally accurate).

The most important tool you can use is a hydrometer. It's the only way you will truly know when your beer is ready...airlock bubbles and other things are faulty.

The only way to truly know what is going on in your fermenter is with your hydrometer. Like I said here in my blog, which I encourage you to read, Think evaluation before action you sure as HELL wouldn't want a doctor to start cutting on you unless he used the proper diagnostic instuments like x-rays first, right? You wouldn't want him to just take a look in your eyes briefly and say "I'm cutting into your chest first thing in the morning." You would want them to use the right diagnostic tools before the slice and dice, right? You'd cry malpractice, I would hope, if they didn't say they were sending you for an MRI and other things before going in....

Fast fermentations/slow fermentations/big krausens/small krausens/bubbles starting and stopping, in the long run is really irrevelent....just that you have fermentation. Yeast don't normal normally die/stop fermenting/get tired, that's a premise new brewers believe, but it's not the truth. Yeast have been doing this for 4,000 years, and know how to ferment the beer, they WANT to ferment the beer, it's their entire purpose in life is to eat sugar, peer alcohol and fart co2 (along with some major screwing during the reproductive phase) especially modern 21st century yeast.

You rack to secondary when fermentation is complete and even a few day later and you determine that by 2 consequitive airlock readings over a 3 day period, not by what the airlock is doing or isn't doing.

so what you're saying is that the airlock will tell me everything i need to know about how fermentation is going? kidding.

thanks for the info. i am still new at this.

is it okay to check the gravity every day or so? i dont want to risk infection.

Also, how do I know what the gravity shoud be so I can determine the fermentation is complete?

Has your temperature gone up recently. Belgian yeasts like higher temperatures.

Just a wild thought; maybe the yeast started well, generating it's own heat, and then as fermentation slowed down, the wort cooled and further slowed the yeast ..... then we had better weather, and the ferment picked up.

What yeast did you use?

You did not mention which yeast you used but Belgian yeasts are a little crazy. I did a Belgian strong dark ale a while ago that showed active signs of fermentation for a full three weeks. I left it in the fermenter for 6 weeks.

I would not check it too often, but sit back let the yeast do it's thing. No need to secondary, just let it sit in the primary. If you are going to transfer it so you can free up the fermenter, you would be better off just buying another fermenter.