OESO. This code tells us two very important things: First of all, the E specifies the mashbill, as mentioned. The second O denotes the yeast strain. The other two letters, the first O and S, are common to all 10 recipes and simply state that these Bourbons are made at Four Roses Distillery and are Kentucky Straight Bourbon Whiskey.

Rich fruit and vanilla

Mash Bill: 75% corn, 20% rye, 5% barley

Kentucky Straight Bourbon Whiskey

ABV: 59.5%
Proof: 119

Age: 10 years, 2 months
Warehouse No.: MW
Barrel no.: 25-4G