I have noticed some trends in the gravity readings of my recent brews:
- The Starting Gravity (SG) is normally within a couple of points of the anticipated SG. I think this is probably explained due to the slightly different volumes transferred into the FV.
- The Final Gravity (FG), however, is always underneath the anticipated FG. I am not sure how much of a problem this is, but it does produce slightly stronger (ABV%) beer than expected.
| Brew | SG Ant | SG Act | SG diff | FG Ant | FG Act | FG diff | Mash in | Yeast | Ferm days |
| 35 | 1060 | 1058 | -2 | 1012 | 1008 | -4 | 66 | WC | 8 |
| 36 | 1053 | 1051 | -2 | 1013 | 1007 | -6 | 65 | LF | 10 |
| 37 | 1052 | 1052 | 0 | 1009 | 1009 | 0 | 65 | S-05 | 11 |
| 38 | 1045 | 1047 | 2 | 1010 | 1007 | -3 | 66 | S-05 | 11 |
| 39 | 1044 | 1044 | 0 | 1008 | 1006 | -2 | 65 | S-05 | 10 |
| 40 | 1043 | 1045 | 2 | 1011 | 1007 | -4 | 66 | WC | 8 |
| 41 | 1037 | 1039 | 2 | 1007 | 1005.5 | -1.5 | 65 | S-05 | 8 |
| 42 | 1043 | 1042 | -1 | 1009 | 1006 | -3 | 66 | Notts | 7 |
| 43 | 1041 | 1045 | 4 | 1010 | 1007 | -3 | 66 | Notts | 7 |
| 44 | 1039 | 1039 | 0 | 1009 | 1005 | -4 | 66 | S-05 | 9 |
| 45 | 1044 | 1043 | -1 | 1008 | 1003 | -5 | 65 | S-05 | 9 |
| 46 | 1045 | 1045 | 0 | 1010 | 1007 | -3 | 66 | S-05 | 10 |
The table above contains the data for the last 12 brews. All of the brews are all grain recipes and the SG/FG calculated using the Grainfather app. I was interested in spotting any potential trends.
- Lallemand Nottingham (“Notts” in the table above) yeast seems to complete fermentation the most quickly.
- White Labs London Fog (“LF” in the table above) produced the biggest difference in Final Gravity. However, this brew required 2 packets of yeast rather than one. This might explain things, but I only have brewed using this once.
- A mash in temperature of 66 rather than 65 seems to be more effective in lowering the FG readings.
- Fermentis S-05 yeast seems to produce some pretty consistent results over a number of different brews.
- It turns out brew number 45 had a wild yeast contamination hence the really low FG. See here for more details.
- Those brews with the most marked difference in FG are where I have extended the 20C fermentation period because there is still a lot of activity in the FV. I wait until the fermentation is starting to slow before increasing the temperature to 23C. So this indicates that a more active fermentation leads to a lower FG. No surprise there then!