"Yeast On Strike" Due to Bad Working Conditions
Fermentation seems to have stopped, but the hydrometer reading isn't where it should be. For beer this is generally around 1.025 and for wine greater than 1.000. This situation is generally referred to as a "stuck fermentation" and can have a couple causes. The simplest cause and probably the most common is temperature. A significant drop in temperature, which is common this time of year, can cause the yeast to go dormant and settle to the bottom of the fermenter. Asking yeast to perform below or at the lower end of the optimal temperature range can result in a prolonged, sluggish fermentation (more than a week for ales, more than three weeks for lagers and wines). If cool temperature is the case, move the fermenter to a warmer area, wrap a blanket around it or a Brew Belt (maintains a constant 75 degrees F) and roust (stir up) the yeast getting them back in suspension. Adding a teaspoon of Yeast Energizer is an added incentive for the yeast to 'get back to work'. This will often fix the problem.
The second most common cause is weak yeast and/or underpitching. Low volumes of healthy yeast will often not be up to the task of completing fermentation. Dry yeast users should always rehydrate rather than just sprinkling the dry yeast on top. A yeast starter is recommended for all types of fermentation, but critical for high gravity worts (above 1.048), lagers, and meads. The solution in the underpitching situation is add more yeast along with a teaspoon of Yeast Energizer.
Extract brewers may experience a perceived stuck fermentation due to the use of low attenuating extracts. Laaglander Dry Malt Extract and John Bull Liquid Malt Extract are known for being high in unfermentable dextrins. These are not bad extracts, in fact they are high quality, but their use is best suited for heavier bodied beers like strong ales, porters and stouts where a higher final gravity is desired.