My last beer went through a normal 10-day fermentation process and afterwards there was no activity. I assumed that most of the sugars had been consumed. But after I bottled my beer and let it carbonate in the bottle for 6 weeks - the taste was still too sweet. Did I use too much base malt or perhaps the yeast gave up too soon?
I'm guessing this was actually an extract brew, so it's likely the wort was mostly fermentable. In the future you can use a hydrometer to measure how much sugars are left in your beer... then you can compare that number to an expected final gravity to make sure it really is time to bottle. If you've got an underattenuated beer sitting in the bottle, you might prepare for a few bottle bombs should the fermentation kick back up. It's amazing the loud explosion they make when they go.
I wouldn't recommend bottling based solely on time and activity (or lack thereof). You never know if you've gotten a stuck fermentation.
Definitely post your recipe, including the yeast strain you used. In addition to everything suggested in the previous answers, note that different yeast strains have different levels of efficiency (known as attenuation). Some ale yeasts will convert as much as 85% of the available sugar, some as low 60%. Lower-attenuation yeast will give you a sweeter beer.
As was mentioned, the only way to know for sure is to take gravity readings. If your current gravity is within the range you'd calculate based on the starting gravity and the attenuation of your yeast strain and it hasn't moved for a few days, it's done. If you're currently showing that, say, only 40% of the fermentables have been consumed, you don't want to bottle it yet.
I bet you added more dextrose or malt then the recipe called for and your beer stopped fermenting because it reached its max ABV for the yeast you used. certain yeasts die at a max AVB and to continue fermenting you must usedifferent yeast such a champagne yeast to obtain higher AVB...made that mistake myself early on and ended up with sweet malty beer that would not carbinate sufficiantly.
As others have said, posting the recipe and hydrometer readings (starting gravity and terminal gravity) would be very useful for a diagnosis.
I'm also going to make the assumption, since you didn't stipulate otherwise, that your beer carbonated in the bottle, which indicates that the yeast is still active.
I can think of a few reasons why the beer tastes too sweet.
You're used to drinking mass produced beer, which finishes very dry. What was the final gravity? Knowing this wold help.
The recipe included a lot of un-fermentable sugars which contribute sweetness to the final product. Usually this comes from a high (>15%) proportion of crystal malts, or a high (>155 F) mashing temperature. Knowing the recipe would help determine if this was the problem.
The yeast you used was low attenuation, high flocculation yeast. These strains (like WYeast British Ale) tend to drop out of the beer before all the sugars are consumed, yielding a sweeter final product. Do you know what yeast you used and what it was rated at for attenuation?
You bottled too soon. The yeast was still actively fermenting the residual sugars and given more time would have dried the beer out. What was the gravity when you bottled? What was the expected terminal gravity?
It depends on a number of factors, beginning with the malts you choose. Sounds like this was an all-grain brew, no?
- What is your recipe? Some malts give more unfermentables.
- What temperature(s) did you mash at. Temperatures favoring alpha amylase (154-162°F) produce more unfermentable sugars.
- What yeast?
- What was the fermentation temperature?
Common enough problem with no simple answers. Most brewers become very used to observing the fermentation progress & know when it's the right time to keg or bottle. YOU DO NOT need to fart around with hydrometer readings at any stage. If the fermentation process is stuck there are some obvious actions you can consider. 1) Accepting the brew is sweet but it can be blended at some future time. 2) Add a reliable kit yeast, they always seem nigh bullet proof & may well be capable of completing the fermentation process. 3) Stir your inactive brew whether you add another yeast or not. 4) Consider pitching a champagne yeast if you had planned a high ABV brew. Be warned all the above may work or none, Been there & it'mighty annoying.