Potential sources of acidity

Soil: As low as pH 5.0
Vegetation: Conifer 4.0,
    broad leaf 5.5
Root veggies: Usually 4.95.6
Fruit: As low as 3.0
Important aspects of a pitcook
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Temperature: Food maintained at 100C, then cools

Acidity: Probably above pH 4, possibly as low as 3