Stuck ferments (was) Re: strange (turbo) mash
Thank you very much for that contribution. It's always nice to get 'hands on' confirmation from those who work day to day in the industry. Your summary reflects exactly what many of the hobbyists have found through trial & error.
Here's my list of causes of stuck fermentations, in order of most-to-least frequent. Check each. Remedy as necessary, one at a time...
1. No oxygen:
- cause - Over-zealously boiling the added water. We see this often with newcomers who have a beer-making history, where sanitation is so much more important.
- remedy - vigorously aerate with an airpump setup or O2 bottle during the first several hours of fermentation (aerobic yeast growth phase).
2. Osmotic pressure:
- cause - Too much sugar, not enough water. We see this usually with newcomers who think (wrongly) that more sugar = more alcohol. It's the old mindset: If a little is good, then more must be better. NOT SO! Not in fermentations anyhow. Too much sugar prevents the yeast cells from absorbing vital water & nutrients across their semi-permeable cell membranes. So they shrivel & die. This relates to Dana's nutrient findings to some degree.
- remedy - Add enough water to bring the madh back into balance i.e. 1 of sugar to 4 of water by weight. Then repitch yeast to replace the dead yeast.
3. Yeast starvation:
- cause - No nitrogen, no nutrients. Just as 'man cannot live by bread alone', so too yeast cannot live by sugar alone. They need food, mainly nitrogen but also vitamins & trace elements just like we do. Sugar & water mashes (thin mash) have almost none of these.
- remedy - Add the missing ingredients in several doses to your fermentation. Follow the instructions of the recipe, or from Dana, Dr Clayton Cone, or any of the nutrient manufacturers. Then re-pitch yeast to re-start the fermentation.
3. Yeast too cold:
- cause - Low ambient temperature or low initial water temp. Yeast has an optimum working temp. & environment. Too cold and it goes dormant, won't multiply or do anything.
- remedy - Use whatever means necessary to raise the temperature to the yeast's ideal working temp and keep it there. Do it SLOOOWLY, so as not to cause shock, which will kill the yeast. If shock does happen, re-pitch the yeast after you've stabilized the temperature.
Some tried 'n' true methods are: to add a portion of warmer water (not 'hot' water); to stand the fermentation vessel in a large tub of warm water; to raise the fermentation room temperature with an electric heater; use heater belts or cables wrapped around the fermenter; use a cooling coil in reverse i.e. pump the mash through the coil that's placed in a warm bath. What method you use will depend on what you have available & where in the world you are. If cold is a problem, always wrap your fermenters in space blankets or similar to insulate them.