Add all ingredients for the cooking liquid except the beer to a blender. Blend until smooth and set aside.
Sear the Meat
Heat a Dutch oven or heavy-bottomed pot over medium-high heat and add the cooking oil.
Add the venison, then season with salt and pepper. Sear on all sides until golden brown.
Deglaze with the Beer
Turn off the heat. Pour the beer into the pot to deglaze. Scrape up the brown bits from the bottom of the pot.
Cook and Serve
Transfer the meat and all of the liquid to the slow cooker. Pour the chile mixture over the meat.
Cover with the lid and cook on the high setting for 6 to 8 hours or until fork-tender.
Carefully remove the venison from the pot and place it into a large bowl. Reserve the cooking liquid in a separate bowl. Shred the meat. Moisten it with enough of the cooking liquid to your liking. Season with salt and pepper.
Transfer the meat back to the slow cooker and place it on the warm setting.
Serve with your favorite toppings.
NOTES
Use the right cuts. Neck, shoulder, shank, and rib meat work best here because they stay juicy and shred better than leaner round cuts.
Blend the chile base first. Add everything except the venison, oil, and beer to a blender and puree it smooth before you start cooking the meat.
Brown the venison well. Season it with salt and pepper, then sear it until browned on both sides, then add the beer. That browning is what gives the barbacoa deeper flavor.
Deglaze with the beer. After searing, pour in the dark beer and scrape up the browned bits from the bottom of the pot, then transfer everything to the slow cooker.
Cook until fork-tender. On high in the slow cooker, plan on 6 to 8 hours, but go by texture more than the clock. The meat is ready when it shreds easily.
Save the cooking liquid. Shred the venison while it is still warm and mix some of the braising liquid back in until the meat is juicy. Do not throw that liquid out.
Reduce the sauce if needed. For a stronger, richer finish, strain the cooking liquid and simmer it on the stove until the flavor and consistency are where you want them, then stir some back into the shredded meat.
Use the oven if needed. If you are not using a slow cooker, cook it covered in a Dutch oven at 300 to 325 F for about 4 hours, or until fork-tender.
Store it with liquid. Keep the shredded venison with some of the cooking liquid so it stays moist. It keeps about 3 days in the refrigerator and freezes well for around 3 months.