The Old European culture blog has spent several posts examining various possible purposes of ancient structures, called fulachta fiadh found in Ireland that are basically wood lined basins in the ground, and has now hit upon a most plausible solution out of many of the proposals, which is that the structures served as facilities for pickling food and possibly also for tanning leather.
There is one thing that I always wondered about fulachta fiadh: why were so many of them built in waterlogged acidic soil, near peat bogs? According to professor Aidan O'Sullivan "fulachta are often found in waterlogged soils by lakes, streams, fens, etc and often close to the edge of a bog. At Killoran fulachta were overwhelmingly located in glacial till at the edges of the bogs".
Every single potential use of fulachta fiadh I have discussed so far would not have been possible if the fulacht fiadh trough was cut into a waterlogged acidic soil. Unless the trough was made absolutely watertight. Which most of them weren't. . . .
Any hole dug in an waterlogged acidic soil would soon fill with acidic water. If the pit was dug in the peat draining area at the edge of the bog, it would soon fill with peat draining water. Whatever the source of the acidic water, the acid in the water would prevent acorns from leaching, would make horrible tasting beer, would make salt extraction through evaporation impossible...So why were so many fulachta fiadh built in waterlogged acidic soils and on the edges of bogs? . . .Bogs are rain fed (ombrotrophic). They need poorly-drained areas, a climate where precipitation exceeds evaporation, and a nutrient-poor environment that favors peat mosses in their ecologic competition against higher plants. Growth of higher plants is also curbed by peat mosses themselves because they bind available nutrients and render the bog water acidic. The acidity comes from the so called low-molecular-weight organic acids (LMWOAs): Formic, acetic, pyruvic, oxalic, malonic, and succinic acids. The amount of these acids in bog water is so high that the pH of bog water is 3-4. This is really acidic indeed. If this bog water is then exposed to the sunshine, it will get even more acidic. . . . solar radiation will degrade organic matter found in bog water and form more low-molecular-weight organic acids (LMWOAs), making the bog water even more acidic. How much more acidic? Not sure what the final pH of the bog water exposed to the sunshine is. But it is definitely low enough to serve as a very good pickling solution.Pickling is the process of preserving or expanding the lifespan of food by immersing in pickling brine (salty and acidic liquid). If the food contains sufficient moisture, a pickling brine may be produced simply by adding dry salt which draws water out of the food creating salty liquid. Natural fermentation at room temperature, by lactic acid bacteria, produces the required acidity creating salty and acidic liquid - pickling brine. If the food does not contain sufficient moisture, pickling can also be achieved by immersion of food in some salty acidic liquid, such as mixture of salty water and vinegar. If you want your pickling to be successful, the pH of the pickling brine has to be 4.6 or lower, which is sufficient to kill most bacteria. The pickling procedure will typically affect both food's texture and flavor but it will preserve otherwise easily perishable food for months or longer. Foods that can be pickled include meats, fruits, eggs, vegetables and milk products like cheese. . . .
Yes but what does pickling has to do with bog water? Who would use bog water for pickling? Well as it turns out a lot of people. And some of them could have been the Bronze Age Irish builders of fulachta fiadh.
As I already said in my post "Fulacht fiadh - meat and fish curing facility", the ancient Irish probably used both salt and smoke curing of meat and fish as a means of preserving it long term. But there is another way Ancient Irish could have preserved food long term without need for salting or smoking.They could have buried it into the peat bog.
It turns out that there are multiple historical examples of food storage in bogs as a preservative and that it can also be used in the tanning of leather.