Peat

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". However according to many other sources, there are actually quite a few fulactha which were set in bogs. For instance a lot of the c.80 burnt mounds on Clare Island seem to be set on bog. 

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. Here are two examples. Look at the gaps between the planks in the first one. And the second one is made from roundwood, impossible to make watertight.

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? To answer that question we need to understand what peat bogs are.

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. 

The article "Photoformation of low-molecular-weight organic acids from brown water dissolved organic matter" by Brinkmann T1, Hörsch P, Sartorius D, Frimmel FH we read:

"This work describes the effects of simulated solar UV light on the bulk properties of dissolved organic matter (DOM) of bog lake water and on the formation of low-molecular-weight organic acids (LMWOAs). By means of size-exclusion chromatography it was shown that the more hydrophilic moieties of the DOM were preferentially photodegraded while the more hydrophobic ones remained relatively unaffected or were even formed. The combined photochemical-biological degradation proved to be more important than the pure photochemical mineralization. Formic, acetic, pyruvic, oxalic, malonic, and succinic acids were identified as important degradation products. Their contribution to the dissolved organic carbon increased from 0.31% before to 6.4% after 24 h irradiation. About 33% of the bioavailable photoproducts of DOM were comprised of these LMWOAs."

Translated into plain English, 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.

Now bog water has a pH of 3-4 before solar irradiation. Well below the required acidity of pickling solutions. For those who don't know much about pH scale, here is a quick overview. The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic and more than 7 is caustic. The scale is not linear but logarithmic. This means that liquid with pH 3 is 10 time more acidic than the liquid with pH 4...

So bog water is 10 time more acidic than what is at minimum required from a pickling solution in order to kill all the harmful bacteria in the food. 

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.  

This is bog butter:

"Bog butter" refers to an ancient waxy substance found buried in peat bogs, particularly in Great Britain and in Ireland. 

In the article entitled "Mysteries of bog butter uncovered" published in the magazine Nature in 2004, we can read that the research by Richard Evershed and his colleagues from the University of Bristol has proven that what is commonly known as the 'bog butter' is the remains of both dairy products and meat encased in the peat.

"Those who live in the countryside of Ireland and Scotland and dig up chunks of peat for fuel have long been familiar with bog butter. While gathering the compressed plant matter, which can be burned in fires, diggers occasionally slice into a white substance with the appearance and texture of paraffin wax. This is thought to be the remains of food once buried in the bog to preserve it. Waterlogged peat is cool and contains very little oxygen, so it can be used as a primitive kind of fridge. The question is what type of food was buried in the peat. Local lore sometimes says that the waxy stuff is literally the remains of butter. For example, the seventeenth-century English writer Samuel Butler remarked in one of his famous poems that butter in Ireland "was seven years buried in a bog". But there could be an alternative source for the waxy material: dead animals. In the eighteenth century, French chemists discovered that human corpses often contain adipocere, a substance also known as 'grave-wax'. So bog butter could be the remains of carcasses rather than dairy products.

To find out, Evershed and his colleagues took a close look at the fatty acids in bog butter. The chains of hydrocarbons in these molecules differ between those derived from dairy and those from meat. They looked at nine samples of bog butter provided by the National Museum of Scotland, some of which are 2000 years old. They reported that six of the bog butter samples come from dairy products, and three are from animal fat (carcasses). So ancient Scots (read here Irish as the term Scot actually means Irish) clearly used the peat to store both types of food."

In the article "Underwater storage techniques preserved meat for early hunters" by Sally Pobojewski we can read about the experiments performed by Daniel C. Fisher, professor of geological and biological sciences at the University of Michigan and the curator of the Museum of Paleontology, who proved that burying meat in the peat bog will perfectly preserve it for two years.  

"From autumn to mid-winter of 1989, Fisher anchored legs of lamb and venison on the bottom of a shallow, open-peat water pond and buried other meat sections in a nearby peat bog. Caches were left in place for up to two years and checked periodically for decomposition. The meat remained essentially fresh for most of the first winter. By spring, progressive discoloration had developed on the outside, but interior tissue looked and smelled reasonably fresh. The combination of cold water temperature and increased acidity in the meat produced by pond bacteria called lactobacilli, which can survive without oxygen, made the meat unpalatable to other bacteria that normally decompose dead tissue, according to Fisher. Laboratory analyses of meat retrieved from the pond and bog in April 1992 showed no significant pathogens and bacterial counts were comparable to levels found in control samples Fisher stored in his home freezer."

So our hunters from the fianna hunting teams could have used the same technique to preserve the meat for the winter. They would bring the animals they have killed to their camp. They would take whatever they wanted to eat on the day, probably internal organs, head and such bits as they are the most perishable. They would cook this as a stew in a pot (not in fulacht fiadh trough :) ). They would maybe even roast some of the animals on a spit over a cooking pit (cooking procedure described in the Irish histories as "cooking using fulacht fiadh"). They would then cut the animal into manageable bits and would place these bits in deep peat bog pits full of acidic peat water, located at the edge of the camp. Or they would bury the meat pieces in deep peat trenches. The meat could then be taken out of the peat storage when needed and either salted and smoked or cooked or sold. 

Professor Fisher suggests that: "Underwater caching turns out to be a simple and effective way to store meat for long periods. Fossils preserved at ancient cache sites suggest it was an important and common part of the winter-to-spring subsistence strategy of Ice Age hunters". 

And we know from the archaeological evidence that this way of preserving meat and fat was as common in Ancient Ireland and Scotland too. 

This article "Carbohydrate polymers in food preservation: an integrated view of the Maillard reaction with special reference to discoveries of preserved foods in Sphagnum-dominated peat bogs" explores possible use of peat in modern food preservation. It mentions that so far "...biodegradable materials that have been found preserved in peat, including carcasses of domestic animals, loaves of bread, dried fruits, berries, and kegs of butter or cheese..."

The article entitled "Peat moss, an old Viking standby, could revolutionize the food-storage industry" says that" Researchers are looking at an old Viking trick--peat moss--as a way of preserving foods and saving millions of dollars per year in refrigeration and transport costs. 

"Scandinavian freshwater fishermen traditionally used peat bogs to preserve their catches until they could pick them up on their way out of the mountains. Fish buried in peat moss or treated with a moss extract stayed fresh weeks longer than untreated fish. And we all know how perishable fish is. 

Dr. Terence Painter, professor emeritus at Norwegian University of Science and Technology in Trondheim who researched preservative abilities of peat says that it can be used for long term preservation of highly perishable food stufs. And they have proven that it is not a lack of oxygen or the presence of a chemical called tannin acting as a preservative which is preventing decay.

Painter and his associates, Yngve Boersheim and Bjoern Christensen, isolated a complex sugar in sphagnum moss, which forms peat bogs after hundreds of years. They set out to prove that the sugar, which they have named sphagnum, was the real preservative in a variety of tests in a government-funded study.

In other tests, the researchers treated 3/4-inch-long zebra fish with peat or extract and left others untreated. After two weeks, the treated fish were fine, while the untreated ones had virtually vanished due to decay.

In a demonstration for the Norwegian state radio network NRK, Christensen opened a plastic container in which a zebra fish had been stored on peat for two years. It was intact and smelled fine. This is incredible considering that fish will start smelling in 2 days unless it was frozen straight after it was caught. 

Fish isn't the only food that may be preserved. Painter said his team has had success with apples, carrots, radishes and other vegetables. Norwegians had a tradition of storing their root plants, such as carrots and turnips, in peat bogs to preserve them.

The researchers have received a Norwegian government grant to start a pilot project testing commercial applications. Painter said it is not clear when the first commercial uses could begin."

This is very very interesting. As I already wrote in my post "Fulacht fiadh - a cooking pit?":

"The cooking hypothesis is rendered even less convincing by the near absolute lack of animal bone or plant material within the troughs. Proponents of this hypothesis have argued that the lack of animal material is likely due to preferential decay associated with elevated soil acidity, which is a key feature of burnt mound sites, of which many are located on marshy uplands..."  

Now in these marshy areas a pit dug into the ground would quickly fill with water. Acidic marshy water. If the pit is dug at the edge of the peat bog, the water would also contain peat water draining from the bog. If your fulacht is located near the bog but not in the bog drain area, you can dig a hole in the bog, get bog water from it and transfer it using pots. Or you can dig some wet peat, and dissolve it in already acidic marshy water filling your fulacth trough. The resulting peat water is exactly what you need for preserving meat and fish. All you would need to do to preserve your meat or fish would be to dunk it into the pit full of peat water and keep doing this until the pit is almost full. 

You could even salt the meat and fish first before you dunk it into the pit, but you don't have to. Once you fill the pit, you would then put some logs on top of it all to press the pit content down so that it stays submerged. You would then cover the pit with planks or thick branches (roundwood) and then with a thick layer of peat to thermally insulate it and that's about it. O yes, you would also need to mark the spot where the pit is, so that you don't accidentally step into it. :)

Once the meat and fish was removed from the pit, there would be no trace left of it to be found by archaeologists today. Except if the meat and fish was for whatever reason forgotten and never taken out. In which case, today, 3000 years later, archaeologists would just find a lump of "bog butter"...

This means that the location of many fulachta fiadh in marshy waterlogged areas near bogs suddenly begins to make sense. Was one of the reason why the hunting camps of the fianna were located near peat bogs because peat bogs were natural meat storage facilities, where large amount of meat from fish and animals killed during the summer hunting season could have been stored and preserved until it was needed later in the year? I believe so. 

But fulachta fiadh which were built in waterlogged acidic soils near peat bogs were not just used for food preservation. The animals, both terrestrial animals and fish, whose meat was preserved in bog water also had skins and they needed to be preserved to. As I already wrote in my post "Fulacht fiadh - tannery", the Bronze Age hunters had several ways of preserving the animal skins and turning them into leather or pelts: vegetable tanning, brain tanning, urine tanning and bran (flour) and salt tanning. All these tanning methods are more or less well known. But there is another tanning method that Fianna could have used, which is almost completely forgotten. 

Peat tanning. 

While I was researching animal skin tanning I came across acid tanning, or pickling. Now acid tanning is not really the best description of this procedure. It should more precisely be called bran (flour), salt and acid tanning. It is basically the same procedure as wet bran (flour) and salt tanning used in Serbia except that additional acid is added to the tanning solution. You can read about the bran (flour) salt tanning in my post "Fulacht fiadh - tannery". Acid tanning is a very fast way to tan animal skins and uses the same principal used in pickling vegetables. Skin is immersed into strong pickle (salty acidic liquid) which kills all bacteria in the skin and also dissolves all non structural proteins and fats in the skin making the skin thinner and easier to work with. 

Here is a short summary of the acid tanning procedure which you can find online on many websites. I will use it to explain how a fulacht fiadh could have been used for this type of tanning. 

According to the most acid tanning instructions, the chemicals required for acid pickling are:

27 liters water

1 kilo bran flakes

1 kilo of plain or pickling salt (not iodized)

0.45 liters of battery acid (from auto parts store)

1 kilo of baking soda

This is a very good video showing how to do acid tanning using battery acid. Any strong acid can be used for skin tanning but battery acid seems to be most popular.

If your fulacht fiadh trough has volume of 150 liters, you would need 5,5 kilos of bran, 5,5 kilos of salt, 5,5 kilos of wood ash and 150 liters of acidic bog water.

Procedure:

"Make sure the skins were fleshed, membraned and salted immediately after the animals were skinned. If the skin was dried for temporary storage, soak the dried skins in clear, fresh water until flexible. "

The streams near which most of the fulachta fiadh were built come handy here. 

"Boil 12 liters of water and pour over one kilo of bran flakes. Let this sit for an hour, then strain the bran flakes out, saving the brownish water solution." 

Bran doesn't really need to be taken out of the solution for it to work. You will just have to later get all the bits out of the fur. So here is how you could achieve this part of the procedure in fulacht fiadh. Let the fulacht fiadh trough fill with fresh bog water, or marshy acidic water into which you have added some wet peat to increase acidity. Leave it to sit exposed to the sun for a day, maybe two. Then boil the water using fire heated stones. Once the water was boiled add bran to it and stir it for a while, and then leave it sit for an hour. 

"Next, bring the remaining four gallons of water to a boil. Put the 16 cups of salt in a plastic trash can. Pour the water over the salt and use the stirring stick to mix until the salt dissolves. Add the brown bran liquid. Stir."

Add more hot stones to the trough until it boils again. Then add salt and mix well so that the salt is all dissolved. 

"When this solution is lukewarm, you are ready to add the battery acid. Read the warning label and first aid advice on the battery acid container. While wearing gloves and an old, long-sleeved shirt, very carefully pour the battery acid down the inside of the trash can into the solution — don't let it splash. Stir the battery acid in thoroughly."

This part can be skipped. We have started with the acidic bog water, which should by now be even more acidic because of the solar radiation and the work of lactic bacteria which is busily decomposing bran and organic matter from the peat and adding lactic acid to the mix. 

"Add the skins to the solution and stir, pressing the skins down carefully under the liquid with the stirring stick until the skins are fully saturated."

Well, get your skins from the stream. They should be nice and plump now. Squeeze the water out of them and then dunk them into the fulacht fiadh trough. 

"Leave the skins to soak for 40 minutes, stirring from time to time to make sure all parts of the skins are exposed to the solution."

I have found recommendations that go from 40 minutes (most common) to 20 days but mostly the duration of pickling is less than an hour. The time it takes to thoroughly pickle the skin will vary depending on the thickness of the skin. You can tell it is completely pickled when the skin is a milky white color all the way through, with no pink color. It is very difficult to say how long it would take to pickle skins in fulacht fiadh trough using bog water as acid solution. But we can try to guess. As I already said, the tanning solution used in the so called "acid tanning", and which we have created in the fulacht fiadh trough, is basically the same solution used in wet bran (flour) and salt tanning in Serbia, with additional acid added to it. Considering that in Serbian wet bran (flour) and salt tanning procedure the skins are left in tanning solution for 3 days, I would say that the time we need to leave skins in the fulacht fiadh trough for anywhere between one hour and 3 days. We should stir the the skins from time to time to make sure all parts of the skins are exposed to the solution. We should also examine the skins from time to time and check if they were white all the way through. 

"Fill your other trash can with clear, lukewarm water. After the soaking is complete. Use the stirring stick to carefully move the skins one by one into the trash can with clear warer. This is the rinsing process, which removes the excess salt from the skins. Stir and slosh the skins for about five minutes, changing the water when it looks dirty."

Take the skins out of the fulacht fiadh trough. Take them to the stream and wash them thoroughly until the water coming out of them is clear. 

"At this point, some people add a box of baking soda to the rinse water. Adding baking soda will neutralize some of the acid in the skin - this is good because there will be less possibility of residual acid in the fur to affect sensitive people. However, this also may cause the preserving effects of the acid to be neutralized. You need to make the choice to use baking soda based on your own end use of the skin. If skin or fur will spend a lot of time in contact with human skin, use the baking soda. If the pelt will be used as a rug or wall hanging, you are probably ok not to use baking soda.

If you decide to use baking soda, place the hide in the neutralizing solution, and stir for 20 minutes. Remove the hide from the neutralizing solution, rinse, and drain."

If you want to wear the skins you are treating or use them as bed covers, you should probably neutralize the acid in them. This is how to do it. You can't use fulacht fiadh trough for this, as it will fill with acidic bog water as soon as you empty it. You will have to use either large pots, like large funerary pots, or you will have to take the skins to another fulacht fiadh which is built in a dry well drained soil and use the trough there, Whatever you decide to do, you will need to use something in place of baking soda, as it was not readily available in Bronze Age Ireland. Baking soda is Alkali. In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. Now when you mix acid (pH < 1) and alkali (pH > 7) you get salts and neutral pH. So where do we find an alkali that can be used instead of baking soda, and that we can use to neutralize acid in the skins we have just pickled?

The word "alkali" is derived from Arabic "al qalīy" (or alkali), meaning the wood ashes, referring to the original source of alkaline substances. A water-extract of burned plant ashes, called potash and composed mostly of potassium carbonate, is mildly basic. After heating this substance with calcium hydroxide (slaked lime), a far more strongly basic substance known as caustic potash (potassium hydroxide) can be produced. But for de-acidifying our skins, we need ordinary weak base - potash. So grab few handfuls of wood ash from your fireplace and chuck it into the pot or fulacht fiadh trough full of clear water. How much will depend on volume of your vessel. For a 150 liters trough you will need 1 kilo of ash. The major components of wood ashes are potassium carbonate (potash) and sodium carbonate (soda ash), and their average pH is about 9,5 while the pH of baking soda is 9.  Mix the solution. Submerge your skins in and leave them soaking for not more than 20 minutes. If you leave your skins in the potash solution for too long, the hair will start slipping (falling off), which is exactly what potash is used for in bucking, as I already described in my post "Fulacht fiadh - tannery".

"Remove the hide from the rinse and hang over a beam to drain. Rub it with some oil, like neatsfoot oil, salmon oil, beechnut oil, to condition the skin."

Hmmm. I am not sure what kind of oils Bronze Age Irish had access to. Probably salmon oil and beechnut oil. So, get the skins out of the potash soulution, squeeze them and then leave them over a branch to drain. Get some oil and rub it into the skins.

"Stretch the hides on a stretcher or hide dryer to finish the process. Place it in a place out of the sun to dry. After a few days the hide should feel dry and flexible. Take it down from the rack and go over the skin side with a wire brush until it has a suede-like appearance. Let the hide finish drying until it is fully dry, which should take a few more days."

This is exactly the same drying procedure used in Serbian wet bran (flour) and salt tanning procedure. Get the skins onto a rack and place them in a shade to dry. Keep an eye on them so that they don't get chewed on by wolves and such things....Take them off when they are dry and that's it...

Now here is the problem with using bog water for this type of tanning. 

The recommendation that I found online is that no matter what acid you use, after mixing the pickle up, the pH level should read below a 2.0. Usually it reads 1.1. You should not let the pH go above 2.5 during pickling, and definitely not above 3.0, because then bacteria will continue to grow. Is our day old bran fortified peat water acidic enough? I have no idea. But as I already said, the tanning solution used in the so called "acid tanning", and which we have created in the fulacht fiadh trough, is basically the same solution used in wet bran (flour) and salt tanning in Serbia, with additional acid added to it. So if bran (wheat) and salt solution is enough to pickle the skins, I would guess that adding highly acidic bog water, which is more acidic than normal vegetable pickle solutions, should make the process even more effective. We know that the pH of the bog water is between 3-4 and that it increases when exposed to sunlight. Is it possible that the final solution has pH below 2,5? Possibly. Whatever the final pH of bog water is, we know that bog water can be used for skin and hair pickling and turning of row skins into pelts and leather. 

The proof are bog bodies.

A bog body is a human cadaver that has been naturally mummified in a peat bog. Unlike most ancient human remains, bog bodies have retained their skin and internal organs due to the unusual conditions of the surrounding area. These conditions include highly acidic water, low temperature, and a lack of oxygen, and combine to preserve but severely tan their skin. While the skin is well-preserved, the bones are generally not, due to the acid in the peat having dissolved the calcium phosphate of bone.

The oldest fleshed bog body is that of the so called "Cashel Man", who dates to 2000 BCE during the Bronze Age.

The best preserved bog bodies in Ireland are:

Clonycavan Man, an iron age bog body dated to 392-201 BC

Oldcroghan Man, an iron age bogman dated to 362-175 BC

The best preserved fleshed bog body is that of the so called "Tollund Man". Tollund Man is a naturally mummified corpse of a man who lived during the 4th century BC.

Now some people will say: "Well these are preserved because they have been kept inside the bogs in anaerobic acidic conditions for thousands of years...The conversion of skin to leather took a long time....This was not a practical procedure which could be used for tanning animal skins..."

Well I am not surprised that you might say that. I had the same doubts myself. But then I came across this. 

Tanbark is the bark of certain species of trees (such as oak) which has high tannin content. It is traditionally used for tanning hides into leather. In some areas of the United States, such as northern California, tanbark is often called "mulch," even by manufacturers and distributors. In these areas, the word "mulch" may refer to peat moss or to very fine tanbark.

Why?

In "A Dictionary of Science" edited by William Thomas Brande and published 1842 we can read that "attempts have been made to separate astringent matter from peat and to use it in tanning leather". 

So it seems that people in the 19th century believed that peat water could be used for tanning leather. Why did they think that? Well because peasants living near bogs have been using bog water for tanning leather for millennia. 

One place where we have records of the use of peat tanning is Strathearn in Scotland.  The Strathearn area of Perthshire lies near the centre of mainland Scotland where Lowlands meet Highlands. It includes the towns and villages of Auchterarder, Blackford, Braco, Bridge of Earn, Comrie, Crieff, Lochearnhead, Muthill & St Fillans. On the blog "PerthshireCrieffStrathearn Local History" in the article "The Rise and Demise of the Leather Tanning Industry in Crieff & Strathearn in the 18th and 19th Centuries" we read this:

"Tanning in the Strathearn  area had been carried out for many years and was known as  “peat moss tanning" . The hides were immersed in a peat hole and left to allow the tannin from the peat to seep into them thus producing a primitive sort of leather. This method began to die out towards the end of the 18th century. The hides would get as tough as a wooden board. Later the shoe maker would come and heat the leather over a fire while rubbing grease into it till it was flexible and make brogues for the family."

This is very interesting don't you think. Well a certain Ernest Edward Munro Payne certainly though so. There a US Patent US1040400 A granted on Oct 8, 1912 to Ernest Edward Munro Payne which describes use of peat water in leather tanning. 

"Be it known that I, ERNEST EDWARD Monro PAYNE, a subject of the King of England, and residing at Aylesbury, in the county of Buckingham, England, have invented certain new and useful improvements in the production of leather, of which the following is a specification. The characteristic feature of this invention is the use, in the production of leather, of a solution of humus (peat) which consists of humic acid, ulmic acid. According to this invention, in producing leather from skin, the skin is prepared as for tannin and is thereafter treated with a solution of humus in alkali (wood ash) and with an acid."

In "The Natural and Agricultural History of Peat-moss Or Turf-bog" by Andrew Steele we can see that originally people believed that the tanning ability of bog water came from tannins from trees which were disolved in the bog water:

Water flowing out of bogs has a characteristic brown color from dissolved peat tannins. However the active tanning ingredient in peat is not tannic acid which indeed is found in most plants, but ulmic, humic and crenic acids. However these acids have the same effect on the skin as tannic acid. 

On top of this, because  peat consists of bits of the plant called sphagnum moss, commonly known as peat moss, it has some additional characteristics which even more increase its tanning ability.

In the book "The Scientific Study of Mummies" by Arthur C. Aufderheide, we can read this chapter about how sphagnum creates tanning effect in peat moss:

So what does science have to say about the ability of peat water to tan skins into leather? Well some scientists are still pondering:

In the article "Determination of functional groups of humic derivatives as tanning-retanning agents" we can read that: 

"Three types of humic acids of different sources have been analysed in order to quantify the functional groups that may be liable to react with the proteins of leather. The quantification serves to determine the extent to which each of these acids can be used as tanning or retanning agents. Humic acids have structures similar to those of vegetable tannins."

Translated into English this means that humic acid found in bog water could have the same or very similar effect on skin turning it into leather, just like tannic acid found in plants. 

But some other scientists have confirmed that skin submerged into bog water "becomes bio-resistant" basically turns into leather...

In the article "Preservation of fish by embedment in Sphagnum moss, peat or holocellulose: experimental proof of the oxopolysaccharidic nature of the preservative substance and of its antimicrobial and tanning action" we can read that 

"Films of mackerel (Scomber scombrus) skin became brown and completely bio-resistant after repeated immersion in aqueous (3% w/v) sphagnan with intermittent drying. Differential thermal analysis (DSC) of the sphagnan-treated skin gave results consistent with tanning by covalent cross-linking."

Sooooo....

We have evidence that until recently people actually used bogs deliberately to preserve food and skin. Even patents were proposed for commercial, industrial use of this technology. 

This sheds a new light on the bog bodies and bog butter... 

What I am trying to say is that people could have deliberately placed food and bodies into bogs to preserve them... To make a miracle preservation pit, you don't need a fulacht trough. All you need is a pit, a hole in the bog, which will fill with bog water. And if you want to use fulacht which is not located in the bog proper, but in the waterlogged marshy area near the peat bog, just dig some wet peat, dunk it into the trough which is already filled with acidic water and mix....

Is this why some fulachta fiadh were originally built in waterlogged acidic soils near bogs? I believe so...