Saturday 20 November 2021

Beerstone is not calcium oxalate and calcium oxalate is not beerstone

This is Graham Dineley writing this blog. All ideas, opinions and mistakes are entirely my own and my responsibility. I welcome comments, please feel free to do so. 

Why am I writing this blog about beerstone? Because it is the one hard, certain and unequivocal piece of evidence for brewing beer in any era. Techniques may vary, but the fundamental processes of turning barley into beer remain invariant, they are dictated by the biochemistry of grain growth. This is the fundamental tenet to Merryn's research, as she states in her thesis and in her most recent publication.

As far as I know nobody has inspected any British prehistoric pottery for traces of beerstone yet. Maybe it is because they do not know what beerstone is, or maybe they have never considered it as a possibility. It could be a useful and productive investigation. Beerstone is robust enough to survive scrubbing, whilst organic residues are not. In fact, it should even be easier to to spot the traces of beerstone on older sherds from those days when scrubbing was a routine operation. 

A recent discovery at the Ness of Brodgar presents an interesting example for analysis for beerstone. A sherd from a Grooved Ware pot has linear parallel striations on the internal surface. The archaeologists and pottery specialist are baffled. 

Why am I discussing barley and not cereals in general? It is because I have, so far, only worked with barley malt and therefore I know only about the fermentation of barley malt causing beerstone.

I have been brewing traditional British cask conditioned ale on a domestic scale, according to Dave Line's wisdom, from his "Big Book of Brewing" for nearly 40 years now. I started with making about 5 or 6 gallons (imperial) at a time from all malted barley grain and have progressed to 10 gallons, the limit of my current mash tun. I feel that I now have some experience and expertise. I have been doing it for long enough to have made most of the possible mistakes and to have learned something from them.

I use modern equipment, plastic and stainless steel for my vessels and electricity for heating, but we have demonstrated the principle of making malt sugars from malt with a wide variety of techniques in our research. However, we have not and do not make our own malt because we have neither the resources, the facilities nor the experience to do so reliably. It is a very skilled process in itself. I rely upon commercially made malt, as I also rely upon commercial yeast. This is to avoid some of the uncertainties of beer production.


In this post I am, of course, referring to the brewer's beerstone, and not the fine limestone that is quarried from the caves behind the Devonshire town of Beer:

Any experienced brewer has encountered beerstone in the course of their activities. It is a robust precipitate of a complex of proteins and amino acids, which lock crystals of calcium oxalate into the matrix. It is a pale brownish pink in appearance, a little like hen's egg shells in texture.


Beerstone can be a problem to modern day brewers as it can harbour bacteria. It can also contaminate equipment and cause problems for further brewing and storage. It is notorious for doing this to aluminium beer kegs. It has never been a particular problem for me so far.

As far as I know beerstone is formed in only three particular circumstances, in heat exchanging wort coolers due to the heat shock, and in fermenting wort in both primary and secondary ( storage ) containers due to the carbonyl ions from the dissolved carbon dioxide. It can also form in beer dispensing lines in a public house. The precipitation process is very slow, so that a container will have to be used repeatedly for a long time to display any accumulation.

Brewing vessels and beerstone

In the archaeological literature I often read about "brewing vats" and "brewing vessels" as if there is only one kind. I have 8 different containers that I use in my brewing.

Demijohns and a siphon tube

demijohn used to drain mash tun

from left to right, sparge water heater, boiler and two primary fermenters 

New mash tun used about 15 times

The new mash tun has an electric heating element. I had to replace the old mash tun when the male steel socket pins became corroded whilst storing it in damp conditions, and would no longer make a good connection with the female plug. Note this is not a gender issue, it is the correct Electrical Engineering terminology. I couldn't find a suitable replacement element. The new mash tun is thermostatically controlled and is much easier to use. Note there is no staining, or any other marks.

old mash tun used over 100 times, note staining but no beerstone

Hamilton Bard beersphere for dispensing beer, used over 1000 times

Interior of beersphere, note beerstone

From left to right, wort transfer vessel, secondary fermenter for storage and two primary fermenters under the sleeping bags for insulation.

Inside of wort transfer vessel, note no staining and no beerstone

Inside of secondary  fermenter/storage vessel used over 1000 times, note beerstone.

The flakes of beerstone in the first illustration came from this fermenter when I scalded it with very hot water. I was trying to eliminate a persistent infection, more about this topic in a later blog. The infection was nothing to do with beerstone. It was, in fact, in the mash tun tap, which I now boil along with the mash bag before use.

Interior of a primary fermenter used about 150 times, note light accumulation of beerstone.

I replaced old primary fermenters with these new ones, when trying to eliminate that same infection.

Interior of boiler, note varnish but no beerstone.

Calcium oxalate is a completely different thing from beerstone. Calcium oxalate is virtually omnipresent in minute traces and so is no indicator of brewing whatsoever. It is present in large quantities in some plants, like rhubarb leaves, where there is sufficient quantities to render them toxic.

Prehistoric brewers did not have wort coolers and neither do I. So the only place that prehistoric beerstone will be found is in the fermenting and storage containers, as do I.

In 1993 Dr Virginia R. Badler and others published a paper on the possibilities for the chemical detection of ancient fermented beverages. As far as I know, it was the first paper on this topic and is a seminal and authoritative work. The first part of the paper is on wine. For her discussion of beerstone see the section "another fermented beverage" on page 412.

Many scholarly academic beer "experts" have never actually made beer, and so have no experience or expertise. Brewing beer is a particularly experiential process, where the subtleties and nuances are necessary and essential for the full understanding. Many of these "experts" confuse beerstone with calcium oxalate. 

Here is a link to an interview of Prof. Pat McGovern by the BeerSmith.

At 4:43 McGovern says the striations on the interior of a pot sherd "are to capture beerstone which is calcium oxalate which has a bitter and even poisonous character". They are in fact to capture yeast, so that when the pot is stored upside down, it will dry in those striations and start a new ferment when fresh wort is added. It is then a "magic pot" that spontaneously starts ferments. Those striations will however also collect beerstone over many uses. This is the sort of thing that Dr Virginia R. Badler identified.

At 7:44 McGovern says that people used to ferment tubers, which are starch rich. Lactic fermentation maybe but not alcoholic, as this requires the action of yeast on sugars, and those tubers must first be converted into sugars. How that could be done? I have no idea, and he doesn't explain that either.

At 13:53 McGovern talks of Marula fruit and drunken elephants. That is a hoary old myth. You need anaerobic fermentation to make alcohol. Rotting fruit is not alcoholic, otherwise we would be drinking rotting fruit bowls.

Finally at 20:52 he says that he has never made a beer but perhaps he should do so for the experience. I agree he should do, and he should use the traditional methods of mashing the malt in a mash tun to make the wort, liquid malt sugars. Then maybe he will know something about what he is trying to talk about in ancient brewing.

I will leave yourselves to judge the rest of his interview.

He has collaborated with Sam Calagione of Dogfish Head breweries, who use malt extracts, syrups and fruit pulp in their brews.

In his second book, "Ancient Brews", all the recipes involve malt extract and other exotic ingredients that were not available until after the industrial revolution. He collaborates with Doug Griffith, who uses the American BIAB or "brew in a bag" technique. This a method that I am unfamiliar with, and seems to me to be a particularly American tradition, where the grains are used for colour and flavour, and not primarily to produce the fermentable sugars.

It seems to me that Professor McGovern is not aware that Prohibition in America completely changed their brewing style, from all grain mashing to produce the fermentable sugars, to a largely extract brewing tradition.

Then there is the Heiss paper "mashes to mashes crust to crust". It is a fascinating paper, with some excellent archaeological examples of grain residues, but the processes in brewing are so sadly ill-informed that it is obvious that they have never made a beer. They use the terms germinated, sprouted and malted as if they refer to the same thing. They are obviously using the archaeological literature for this. There is no illustration of these things so that it is impossible to see what they are actually talking about. 

They seem to think that a few barley grains grown in a Petri dish is malt, but without any illustrations it is difficult to tell just exactly what they were analysing.

In their diagram of the chaine operatoire of brewing, they mention calcium oxalate in actions 6, 7 and 8. Chaine operatoire is an anthropological phrase and it has no place in brewing science and technology. There is so much wrong with this illustration below. Brewing beer is not a two step process. It takes at least 3 steps, 1) malting the grain, 2) making the wort, or liquid sugars and 3) fermenting that wort.

chaine operatoire of brewing actions acc to Heiss et al (2020)

Action 1: "soaking". The correct term is steeping or imbibification. The grain is a living organism and needs to breathe, otherwise it will drown. It needs oxygen and ventilation. The traditional way on Orkney is to place the grain in a sack in a bubbling stream, or if using a steeping container it needs frequent air rests.

Action 2: "sprouting". Once the grain begins to show signs of growth, after 2 or 3 days depending on the ambient temperature it is ready. "Twa Taes" is the Orcadian phrase, or "two toes". It must then be turned out onto the malting floor and turned and raked to confuse the geotropism and inhibit the growth of the shoot  for the next 4 or 5 days. Again, this depends upon the ambient temperature, and will not work successfully if the grain bed temperature exceeds 20°C. Any growth of the shoot is lost potential sugars, for that starch is lost to growth which could have been converted into sugars in the mash tun by the enzymes produced in the malting process. This flooring also allows the grain to complete germination, without growth, and for the proteolytic enzymes to degrade the protein matrix that binds the starch granules together. This make the malt friable and easy to crush when dried.

Action 3: "drying or roasting". The green malt must be gently dried at a low temperature over 2 or 3 days, to preserve the enzymes. Roasted malts have been introduced after the industrial revolution, when coke was used to dry the malt. Coke produces pale malt which has a better conversion, but the lacks the colour and flavour of traditional fuel fired kilning. Kilning can be a confusing term, because most people think of pottery kilns, which are run at high temperatures. Grain (corn and malt) kilns must be run at a low temperature, to preserve the seed corn for germination. This not the archaeological "parching". The malt must also be dried at a low temperature to preserve the enzymes for later conversion. This not roasting. 

All this was known long ago, before scientific explanations, as preserving the "spirit" of the grain, see Stopes (1885).

Nowadays these 3 stages are performed in huge, highly technical rotating drums on an industrial scale, but again the processes remain the same.

Action 5: "crushing or grinding". Malt must be crushed to preserve the husks, they perform an important role in filtering the wort during lautering and sparging.

Actions 6 and 7: "soaking and heating". These are actually one process, mashing. One easy way of mashing is to raise the water temperature to about 74°C, and then adding the crushed malt, the strike. The temperature is lowered by the malt to the desired 65-67°C and maintained at this temperature for about an hour or so for the enzymes in the malt to convert to starches into malt sugars. The harder way is to start from cold, and to slowly raise the temperature to the conversion point and then to hold it there for the hour or so.

Action 8: "fermentation". This is the only stage that causes beerstone to be precipitated.

I think that the authors of this paper would benefit from making a beer too. Then perhaps they would also understand what they are trying to talk about.

That fact that they have 197 entries in their Bibliography reminds me of the old joke about the bespoke tailor, "Never mind the quality, feel the width."  Many of them are obscure and not easily accessible.

This is not Science as I know it!



A recent paper by Oliver E. Craig discusses several types of fermentation including the potential for identifying 'cereal fermentation' on pottery. He thinks that the use of the Feigl Spot test to identify fermentation is inconclusive and controversial:

"The chemical identification of fermented alcoholic beverages is one of the most controversial areas of biomolecular archaeology, and few claims are accepted without challenge."

He goes on to say that:

"Even though, as noted above, there is no reason to dispute these claims on theoretical or contextual grounds, the chemical analysis is lacking. These claims invariably rely on the detection of calcium oxalate (a major component of “beerstone”) using a chemical spot test (Feigl 1956), which would seem wholly inappropriate considering that the test itself is not specific to the target analyte and that the oxalates may occur in many substances other than beerstone."

Since he talks of 'fermenting cereals' and not malt and malt sugars, it seems to me that he has no practical experience of brewing ale or beer or of beerstone.

If you don’t know what you are looking for how do you know whether or not you have found it?

This lack of knowledge is exemplified by our visit to a Viking age archaeological site on Orkney, Snusgar. When we asked one of the archaeologists “Have you found any evidence for brewing?”, they replied “None whatsoever.” We asked “Have you any idea what to look for?”, they replied “I haven’t got a clue.”

Dr Virginia R. Badler had first identified the beerstone on the inside surface of a pot sherd from Godin Tepe. She then confirmed this identification with the Feigl spot test.

I note that most of the entries in the Bibliography are from archaeological or anthropological literature. It is as if the archaeological community believe that the “font of all wisdom” resides entirely within their community. Archaeologists frequently talk of interdisciplinary research, but I think that until they step outside of their community and embrace malting and brewing science, they will make no significant progress in understanding and identifying the archaeological evidence for making malt, malt sugars, wort, ale and beer.

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