Gravity reading as it applies to fermentation

There's a sticky thread above that states:

If at 3 days nothing seems to of happened then take a gravity reading to make sure you haven't missed the fermentation.

What should I be looking for? My SG was 1.076. In other words, what number will tell me that the fermentation is occurring?

Anything lower than your OG. If there is no fermentation, there will be no reduction in gravity.

As I understand it (Which could be wrong) Gravity is a measure of the sugar concentration in the beer, as the yeast feeds on the sugar (fermentation) the concentration lowers, lowering gravity.

As master kenobie states, if your gravity has lowered at all you have fermentation. Not all fermentations are vigorous and that is not always a bad sign if you don't see something going on. High SG you have there though, did you make a starter and did you aerate? also, are you fermenting in a bucket or a carboy?

bowiefan said:

High SG you have there though, did you make a starter and did you aerate? also, are you fermenting in a bucket or a carboy?

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It is a high SG, but within the manufacturer's/recipe's guidelines (it's a higher-alcohol Holiday Ale). I used the dry yeast that came with the kit, and I rehydrated it in some warm water & wort. It frothed up quite a bit, so I know my water was not too hot. I aerated by shaking and rolling the carboy. My fermenter is a 6.5-gal glass carboy.

I just checked it, and there is krausen. The airlock has a slow blip. blip. blip. but nothing vigorous. I think I'm ok.

The rule of thumb is that you can tell when fermentation is over when you get the same specific gravity reading over a period of 3 days. In other words you take a reading on one day, record it and come back 2 days later for another reading, which if the same tells you fermentation is over.

Be careful shaking and rolling a carboy around.

The Gravity reading is not just a measure of the concentration of sugar in water because there is also alcohol which is a lower gravity than water.

Sneaker said:

It is a high SG, but within the manufacturer's/recipe's guidelines (it's a higher-alcohol Holiday Ale). I used the dry yeast that came with the kit, and I rehydrated it in some warm water & wort. It frothed up quite a bit, so I know my water was not too hot. I aerated by shaking and rolling the carboy. My fermenter is a 6.5-gal glass carboy.

I just checked it, and there is krausen. The airlock has a slow blip. blip. blip. but nothing vigorous. I think I'm ok.

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Ok, I asked about the type of fermenter to know if you could see what was going on inside or if you were just relying on the airlock as an indicator.
As a rule of thumb, it is always a good idea to make a starter, But especially if you are starting with a gravity above 1.060. Once you cross the 60 line your yeasties have a tendancy to get very stressed towards the end of fermentation due to the high alcohol level. This can lead to a stuck fermentation, but most frequently cause fermentation to take a really long time and finish up a bit high. Be patient with that beer, give it at least 3 weeks before you check your gravity again, and read up on how to un-stick a fermentation in the meanwhile just in case. In any case you have not made a major mistake, you just might have to take an extra step before you can drink your beer.