This is a good place to begin as it has many recipes for making different types of alcohol from sugar washes to AG (all grain) along with proper proportions. We suggest new members start here and then once they feel comfortable with fermentation then venture out and try mixing, matching, or developing a recipe of their own.
The fermentation process has limits such as temperature. Greater than 80F or 27C can kill the yeast and less than 59F or 15C will slow down the yeast activity. Not all sugars are fermentable. Non fermentable sugars in solution will remain after fermentation and will result in a sweeter end product. Usually the fermentation is done when the mash/wash goes from sweet at the beginning to sour at the end of fermentation.
Another limitation would be the type of yeast, brewer's yeast tolerate up to about 5% alcohol. Beyond this alcohol level the yeast cannot continue fermentation. Wine yeast on the other hand tolerates up to about 12% alcohol. The level of alcohol tolerance by yeast varies from 5% to about 21% depending on yeast strain and environmental conditions.
We have two phases of fermentation: the first phase is when the yeast adapts to their environment just before starting to consume the sugar, the second phase is called attenuation this is the phase that fermentation actually occurs.
Some folks gauge this on their airlock bubbling, the airlock bubbles because the yeast are eating up sugar and producing CO2. The CO2 builds up pressure and escapes through the airlock. The problem with relying solely on this is if you have a leak then the pressure escapes through the leak which in turn reduces airlock activity. Another factor is the CO2 might dissolve back into the wash which also reduces the activity. This is why it is important to use a hydrometer sometimes referred to as an SG meter which is an instrument that measures the weight or gravity of a liquid in relation to the weight of water. Also might be referred to as wine or triple scale hydrometer for measuring sugar content in washes. (SG) refers to Specific Gravity, when checking on fermentation you use this hydrometer to take an (OG) Original Gravity reading prior to pitching your yeast. Then as the yeast ferment (eat the sugar) the density of water drops… you take another gravity reading which is called a (FG) Final Gravity reading. When yeast finishes the fermentation process, they shut down, clump together, and fall to the bottom of the fermentor, this term is called "flocculate". When yeast flocculate, it is easy to see that fermentation is done. For more information about using a hydrometer refer to the Mash Hydrometer section.
Attenuation varies between different strains of yeasts. The fermentation conditions and gravity of a particular beer will cause the attenuation to vary; hence each strain of yeast has a characteristic attenuation range. The range for yeast is typically between 60-85%.
How do you calculate attenuation?
To calculate attenuation percentage or abv of wash, the following equation can be used:
[(OG-FG)/(OG-1)] x 100. Also there are several different methods found in the Mash Hydrometer section.
Temperature can also be a factor as yeast doesn’t like temperature swings, they like temperature to be stable. Raising the temperature gets them working faster, but produces more off flavors and sometimes fusel alcohols if you go high enough. This is one reason we choose not to use Turbo yeast here on HD as mentioned rapid fermentation creates off tastes and even carbon filtering will not get rid of it. As mentioned many times on the forum "if the wash is done properly, distilled properly, and cuts made correctly, there is no need for carbon filtering". Too low of a temperature on the other hand seems to put them to sleep or as mentioned above causes it to flocculate, thus it is important to keep your temperature as stable as possible to insure good attenuation. A good follow-up to what might cause a stalled wash/mash is Lampshades post on Stalled fermentation trouble shooting guide.