[ltoews]

The most important part of the batch code is the third through seventh numbers. Here is an example of a batch code: 122027436100 B

There are always going to be two letters or numbers at the beginning of the code, which is the blending facility code, the third and fourth number of the code is the year minus 1. The fifth, sixth and seventh numbers of the code are the days left in the year. So, in my example, that means it was made on the 91st day of the year, April 1, 2019 (365 – 274 = 91)

Breaking down the code
12: The designator of the plant that manufactured the DEF
20: The year of manufacture minus 1, so this DEF was made in 2019
274: Days left in the year. 365 – 274 = 91, so the 91st day of the year, or April 1
36100: The batch code

• Specification life for DEF is 2 years at 75F or so.
• Storage life is highly dependent on temperature. DEF stored at 85F only lasts 12 months. Storage above 95F (not unusual in a vehicle parked in the sun during the summer) is limited to 1 month or so. Reason: The urea in DEF decomposes and creates ammonia liquid and vapor in the jug, causing issues when you open it, and reducing the amount of urea in the DEF when it is used in the vehicle.
• DON’T buy old DEF jugs. When buying DEF in jugs, look at the code. Find a jug made in current year and with the lowest three-digit number you can find in the 5th, 6th and 7th digits. Store it in a cool location out of the sunlight.
• Buy DEF from stores that are likely to move a lot of inventory, have controls on inventory age, and are air conditioned. Not that it is a guarantee, but big-name outfits are likely a good bet.
• DON’T buy jugs of DEF at a gas station that stores them outside, or have obvious signs of degradation like leaks, crystals on the box or jug, or are off color.