After trying to pick the best match on a SRM chart I realized my eyeball was pretty bad at making the call. This probably gets better with practice but, like paint chips, it all depends on ambient lighting and chip color variation and so on. I found several online SRM image charts but all are on a glowing screen in 2D and don't capture the transparency factor of the liquid. After asking other family members to "make the call" when comparing to the chart, I got answers ranging from 7 to 12. I then stumbled on a guy that had used Soy sauce as a color match reference and thought I'd try it. Here is the formula I derived from his data. SRM = soy grams/(final grams- soy grams) * 270 I used two identical small bottles, put reference beer in one and 2 grams of Soy in the other ... diluting the soy gradually with water until the two vials matched. This was VERY EASY to tell when they we the same. Same light transmission, volume, and light source. I ended up with 61 grams of final mix. Using the formula above this gave me an SRM of 9.1. Cool! the 270 might vary a bit depending on soy brand but it seemed right in the middle of the "best guess" range. Not sure I would do this every time but its a good standard tool to compare batches and slight recipe changes that might not show up as obvious I'd post a picture but not figured out the process yet.
