Ambient room temperature is never the same temperature as fluid. Fluids usually have a lower temperature than the surrounding air. Measuring temperature with a liquid thermometer is strongly recommended.
Check the calibration of your hydrometer. At 60°F, H20 (soft) should read 1.000 S.G. Remember that different temperatures will give variations in S.G. readings. Keeping liquid temperatures between 68 – 74°F will allow consistent S.G. readings. Keep fermentation vessels away from “heat-sinking” areas, i.e. concrete floors, windows, doors, walls with exterior exposure, and any areas where temperature can vary. Brew belts or heating pads (used with a blanket) are excellent ways to ensure constant fermentation temperature.
TEMPERATURE AND FERMENTATION
Keep your carboys warm during cold winter months. Many times the simple explanation is temperature. Remember that yeasts, just like people, get pretty sedate in cold weather. The result can mean sluggish or stuck fermentations, excessive carbonation of wine and/or prolonged clearing periods. In order to reduce these possibilities, please ensure a constant temperature of 68 – 74°F for your must, and be sure to keep the following points in mind: If you do have slow or stuck fermentation, try moving your beer or wine to a warmer area, give it a gentle stir, or use a yeast starter to re-start your yeast. Paying extra care and attention to the points above will go a long way to ensuring consistent success (and reducing any unwanted hassles).
< 45°F (7°C) Stuck Fermentation
50–60°F (10–15°C) Slow Fermentation
65–75°F (18–24°C) Normal Fermentation
80–115°F (27–46°C) Very Rapid Fermentation
120°F (49°C) Death