Slice the meat against the grain into long strips, 2 to 3 cm thick and 5 to 7 cm wide. Uniformity matters for even drying. Remove every trace of fat and sinew. Fat will not dry properly and will cause the meat to spoil rather than preserve. This step is not optional.
Oven method: Lay the strips on a wire rack set over a baking sheet. Place in the oven at the lowest possible temperature, 170°F or below. Prop the oven door open slightly with a wooden spoon to allow moisture to escape continuously. Dry for 6 to 8 hours until the strips are completely rigid, dark brown, and snap rather than bend when pressure is applied. If they bend at all they are not done.
Dehydrator method: Lay strips on dehydrator trays with space between each piece. Set to 160°F and run for 6 to 8 hours until completely rigid and hard.
To store: Break the dried strips into smaller pieces and grind coarsely in a food processor or pound in a mortar until you have a rough, fibrous powder. Store in a cloth or linen bag, not airtight. In dry conditions it will keep for months.
To eat as broth: Take a small handful of ground borts powder and add to a cup of boiling water. Let it rehydrate for 5 to 10 minutes. Drink the resulting broth directly from the bowl.
To eat as reconstituted meat: Soak larger pieces of borts in cold water overnight until rehydrated. Add to a pot of boiling water with wild onion, millet or scallions. Simmer for 30 to 45 minutes until completely tender.