Why Is My Brew’s Final Gravity Too High?

Reading your hydrometer a couple weeks into fermentation and seeing that you are a few points above your target FG is not exactly the best feeling when you first start brewing. At least that was the case when I started brewing, but then again, I wasn’t sure why I was taking a reading to begin with and what happens when your gravity is too high?

Well, first things first… you have to realize that you are simply checking to see how dense the liquid is. Since you added sugar from malted barley, the water has to weigh more. When you are taking a hydrometer reading you are simply checking to see whether or not the yeast has turned that sugar into alcohol…

Normally a vial of yeast will eat approximately 65 to 77% of sugars depending on the yeast strain and the ingredients you use. So if your original gravity say was 1.050, you should be finishing around 1.012 to 1.018, which is 23 to 35%. In other words, you are left with what the yeast doesn’t eat.

I remember brewing an Imperial Stout once and was expecting to finish around 1.022, but ended up closer to 1.030!!! Being one of my first batches, I freaked out and thought the world had come to an end and that I had just spoiled a beer… so much for the $90 worth of ingredients, 7 hours of brewing and 6 weeks of waiting… fortunately the beer was actually amazing (possibly one of my best batches ever) and it taught me a lesson… sometimes numbers don’t matter, it matters what the beer tastes like…

I know this is common and that most brewers who don’t reach their estimated Final Gravity are worrying needlessly and that they will end up with good beers. However, I am also aware of those occasion on which brewers will experience a stuck fermentation and may need to do something about it.

The most common cause I know of for stuck fermentation is temperature fluctuation. If you have yet to invest money in equipment to control your temperature, that should become your next brewing priority. By equipment, I don’t mean a special fridge or anything that will cost you more than $10 bucks… You can simply go buy one of those big plastic storage containers when you can fit your bucket or carboy and fill it up with water… By doing so, you will not have as much fluctuation in temperatures because there is more mass that needs to be cooled or heated.

Ideally, you would want to get a small fridge or convert a big fridge into a kegerator and use that. Most small fridges, like the ones they use at college dorms can’t fit a carboy or bucket. The ones I’ve found that work best are the wine fridges that have the racks for bottles which are easily removed.

The reason why temperature control is so important is because when you let temperature raise, the yeast start fermenting faster and produce more by-products and esters which can give your beer different off-flavors. If you let your temperature drop, the yeast tend to slow fermentation and even go dormant which causes them to flocculate and stop fermenting entirely.

2 to 3 degrees is enough to cause these kinds of things and I’ve noticed that most problems occur when people ferment their beer in their closets or somewhere exposed to ambient temperature which tends to be hotter during the day and colder at night. If your fermenting temperature went through this, then this is likely the reason why your beer stopped fermenting. If raising the temperature up a bit and stirring lightly won’t reactivate the yeast, then you may need to re-pitch a little more. This is an extreme case. Most of the time if you’ve fermented less than 65% then you may want to re-pitch, but if you fermented at least 65% then chances are your beer is done and you don’t need to re-pitch yeast.