BrandonBCA
02-17-2011, 07:07 PM
From reading this forum, I gather most use only sugar+yeast in their recipes for DIY CO2. While this can be effective in the short term, it will waste sugar, and produce a far less stable cycle of CO2 generation(sharp peaks). A little understanding of the processes going on in your fermenters will help get the most from your yeast and more constant production of CO2.
First off the reaction we're most interested in is:
Sugar+phosphate+pyruvate=ethanol+CO2+ATP
The goal of a good recipe should attempt to maximize the utilization of the sugar to the maximum levels of alcohol tolerated by the yeast, which sugar water will not provide. How you provide these nutrients is optional, and there are numerous possiblities so you can just use what you have on hand. Some of these options would be fish food, molasses, a vitamin rich juice, multivitamins or a specific yeast nutrient. This list is not exhaustive.
Yeast cells contain all the nutrients needed for yeast, but due to their thick cell membranes they are not readily available. If you wish to make your own yeast nutrient you will need to lyse the yeasts cell walls. The way to accomplish this is to heat kill the yeast in an acid(lemon juice works well) solution, then freeze it(in a small ice cube tray for easy dosage) to completely pop the membranes. The heat kill is similar to a pasteurization process, whereby you boil the yeast+acid at a rolling boil for ~15 minutes.
Of minor note, as the fermentation progresses the yeasts ability to process certain forms of phosphate and nitrogen is lessened, so for commercial yeast nutrients ammonium salts of phosphate(specifically DAP) are added in addition to the traditional yeast nutrient.
Rehydration yeast nutrients(such as Go-Ferm) are largely unnecessary for our purposes, but a fermentation extending yeast nutrient(such as Fermaid K) are reasonably priced, long lasting and necessary for a complete fermentation. If you live somewhere it is available marmite, vegemite and other lysed yeast extracts will work well as a nutrient. This is not the same as the nutritional yeast or brewers yeast sold in drug stores.
Different yeasts have different characteristics in their fermentations. The four characteristics we are most interested in are:
1)stability of production
2)total alcohol production
3)flocculance-it's the gunk that gets in the lines
4)operating temperature
Yeasts are broadly categorized into beer,baker's, wine, and fuel yeast strands. I will not discuss fuel yeasts since they are not readily available to the buying public.
Beer yeasts are high flocculants with low alcohol tolerance, fast fermentations, and high operating temperatures. None of these characteristics make them ideal for our purposes.
Baker's yeasts are high flocculants with middling alcohol tolerance(~13%), moderate fermentation periods and moderate operating temperatures. They are adequate for the CO2 generators, especially if low flocculant producing foods are fed. The amount of sugar in solution that would get the best yield is to a specific gravity of ~1.1, which would be about 5 cups/gallon or 1 1/4 cups/liter.
Wine yeasts are low flocculants with the highest alcohol tolerance among readily available yeasts, have the lowest operating temperatures(Around 55F) and produce the slowest, most easily predictable CO2 yields. All of these characteristics make them the ideal yeast to use in our ferment generators, especially for those of us who like to keep the thermostat down this time of year.
Finally, shaking the bottle is neither necessary nor harmful. Commercial beer fermentation often uses a continuous fermentation process, in which the beer is continually stirred for an even flavor/to speed up the reaction. The only way I can figure this bit of nonsense got injected into the DIY culture is through a misunderstanding of directions on breadmakers, where they say not to mix the yeast in a timed-bake batch. This is purely to keep the yeast from hydrating early, just as you wouldn't want your coffee grounds wet in a delay brew coffee situation.
First off the reaction we're most interested in is:
Sugar+phosphate+pyruvate=ethanol+CO2+ATP
The goal of a good recipe should attempt to maximize the utilization of the sugar to the maximum levels of alcohol tolerated by the yeast, which sugar water will not provide. How you provide these nutrients is optional, and there are numerous possiblities so you can just use what you have on hand. Some of these options would be fish food, molasses, a vitamin rich juice, multivitamins or a specific yeast nutrient. This list is not exhaustive.
Yeast cells contain all the nutrients needed for yeast, but due to their thick cell membranes they are not readily available. If you wish to make your own yeast nutrient you will need to lyse the yeasts cell walls. The way to accomplish this is to heat kill the yeast in an acid(lemon juice works well) solution, then freeze it(in a small ice cube tray for easy dosage) to completely pop the membranes. The heat kill is similar to a pasteurization process, whereby you boil the yeast+acid at a rolling boil for ~15 minutes.
Of minor note, as the fermentation progresses the yeasts ability to process certain forms of phosphate and nitrogen is lessened, so for commercial yeast nutrients ammonium salts of phosphate(specifically DAP) are added in addition to the traditional yeast nutrient.
Rehydration yeast nutrients(such as Go-Ferm) are largely unnecessary for our purposes, but a fermentation extending yeast nutrient(such as Fermaid K) are reasonably priced, long lasting and necessary for a complete fermentation. If you live somewhere it is available marmite, vegemite and other lysed yeast extracts will work well as a nutrient. This is not the same as the nutritional yeast or brewers yeast sold in drug stores.
Different yeasts have different characteristics in their fermentations. The four characteristics we are most interested in are:
1)stability of production
2)total alcohol production
3)flocculance-it's the gunk that gets in the lines
4)operating temperature
Yeasts are broadly categorized into beer,baker's, wine, and fuel yeast strands. I will not discuss fuel yeasts since they are not readily available to the buying public.
Beer yeasts are high flocculants with low alcohol tolerance, fast fermentations, and high operating temperatures. None of these characteristics make them ideal for our purposes.
Baker's yeasts are high flocculants with middling alcohol tolerance(~13%), moderate fermentation periods and moderate operating temperatures. They are adequate for the CO2 generators, especially if low flocculant producing foods are fed. The amount of sugar in solution that would get the best yield is to a specific gravity of ~1.1, which would be about 5 cups/gallon or 1 1/4 cups/liter.
Wine yeasts are low flocculants with the highest alcohol tolerance among readily available yeasts, have the lowest operating temperatures(Around 55F) and produce the slowest, most easily predictable CO2 yields. All of these characteristics make them the ideal yeast to use in our ferment generators, especially for those of us who like to keep the thermostat down this time of year.
Finally, shaking the bottle is neither necessary nor harmful. Commercial beer fermentation often uses a continuous fermentation process, in which the beer is continually stirred for an even flavor/to speed up the reaction. The only way I can figure this bit of nonsense got injected into the DIY culture is through a misunderstanding of directions on breadmakers, where they say not to mix the yeast in a timed-bake batch. This is purely to keep the yeast from hydrating early, just as you wouldn't want your coffee grounds wet in a delay brew coffee situation.