The books / Mead Making / chapter 5 of 21
The alcohol is the gravity you lost
All chapters
- Honey, water and yeast
- Why mead goes wrong
- Never boil the must
- Honey and gravity
- The alcohol is the gravity you lost
- Choosing a yeast
- Feed it in thirds
- Sanitise everything it touches
- The cellar through the year
- Three steady readings
- Racking off the lees
- Faults and what caused them
- A stuck ferment and the restart
- Clearing, fining and the second racking
- Stabilise before you sweeten
- Dry, semi-sweet and sweet
- Bottling
- Varietal meads
- Patience is a technique
- Selling mead, and the licence
- What the cellar leaves out
Yeast turns sugar into alcohol and carbon dioxide, and alcohol is lighter than water, so the gravity falls as it works. Measure at the start and at the end, and the difference tells you how strong the mead is: alcohol by volume is the original gravity minus the final gravity, times 131.25.
A standard mead from 1.100 that ferments right down to 1.000 lost 0.100, which is 13.1 percent. A session mead from 1.050 ends at 6.6. The formula is an approximation that drifts at very high gravity, but it is the one the hobby uses.
A yeast stops when the alcohol reaches its tolerance, whatever sugar is left.
In this game a mead ferments to 1.000 when its yeast can take it there. When it cannot, it stops at the yeast's limit: a sack from 1.140 with a 14 percent yeast finishes at 1.033, sweet.