Reading your hydrometer a couple of weeks into fermentation and seeing that you’re a few points over your target FG isn’t exactly the best feeling when you start brewing. At least that was the case when I started brewing, but then again, I wasn’t sure why it was taking a reading to begin with, and what happens when its 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 malted barley sugar, the water has to weigh more. When you’re taking a hydrometer reading, you’re simply checking whether or not the yeast has converted the sugar to alcohol…

Typically, a vial of yeast will consume approximately 65-77% of the sugars, depending on the yeast strain and the ingredients you use. So if your original gravity was 1.050, you should be ending up around 1.012 to 1.018, which is 23 to 35%. In other words, you are left with what the yeast does not eat.

I remember brewing an Imperial Stout once and hoping 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 I had just spoiled a beer…so much for the $90 in ingredients, 7 hours of brewing, and 6 weeks of waiting… .thankfully the beer was amazing (possibly one of my best batches ever) and taught me a lesson… sometimes the numbers don’t matter, the taste of the beer matters…

I know this is common and most brewers who don’t hit their estimated final gravity are worrying needlessly and will end up with good beers. However, I am also aware of those times when brewers will experience stalled fermentation and may need to do something about it.

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

Ideally, you would buy a small fridge or convert a full size fridge into a kegerator and use it. Most small refrigerators, like the ones you use in college dorm rooms, can’t fit a carafe or bucket. The ones I’ve found work best are wine coolers that have easily removable bottle racks.

The reason temperature control is so important is because when you let the temperature rise, the yeast starts to ferment faster and produces more byproducts and esters that can give your beer different off-flavors. If you let the temperature drop, the yeast tends to slow down fermentation and even go dormant, causing them to flocculate and stop fermenting altogether.

2-3 degrees is enough to cause this sort of thing and I’ve noticed that most problems occur when people ferment their beer in their cabinets or somewhere exposed to room temperature which tends to get hotter during the day and colder at night. If your fermentation temperature went through this, then this is probably why your beer stopped fermenting. If raising the temperature a bit and stirring lightly doesn’t reactivate the yeast, you may need to add a bit more. This is an extreme case. Most of the time, if you’ve fermented less than 65%, you may want to pitch again, but if you’ve fermented at least 65%, your beer is probably done and you don’t need to pitch the yeast again.