Eggs and Invisible Ink: George and Giovanni

By Sean Coughlin

In a 2015 episode of Turn, a US Revolutionary War TV drama on AMC, George Washington’s spy Abraham Woodhull uses a special ink made with alum to write secret messages under the shells of hard-boiled eggs. The technique was also advertised on the show’s Twitter in 2014, a year before the episode aired (Figure 1).

Figure 1: Teaser tweet before the airing of the episode. Image via AMC Twitter.

Turn is based on a 2006 book by Alexander Rose called Washington’s Spies: The Story of America’s First Spy Ring, but there is no mention in the book of any such technique. Instead, it seems to come from a 2009 book by John A. Nagy, Invisible Ink: Spycraft of the American Revolution. That book describes an ink that is able to permeate the shell of a hard-boiled egg, leaving the message hidden inside and no trace of writing on the shell. It is not attributed to George Washington and his spies, however, but to Giambattista della Porta. Nagy writes:

“In the fifteenth century Italian scientist Giovanni Porta described how to conceal a message in a hard-boiled egg. An ink is made with an ounce of alum and a pint of vinegar. This special penetrating ink is then used to write on the hard-boiled egg shell. The solution penetrates the shell leaving no visible trace and is deposited on the surfaced of the hardened egg. When the shell is removed, the message can be read.” (John A. Nagy, Invisible Ink: Spycraft of the American Revolution, 2009: 7)

Nagy’s account of della Porta’s recipe seems in turn to have come from 1999 book by Simon Singh called The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography. Singh, however, leaves it unclear whether the egg is to be hard-boiled or raw when one writes on it:

“In the fifteenth century, the Italian scientist Giovanni Porta described how to conceal a message within a hard-boiled egg by making an ink from a mixture of one ounce of alum and a pint of vinegar, and then using it to write on the shell. The solution penetrates the porous shell, and leaves a message on the surface of the hardened egg albumen, which can be read only when the shell is removed.” (Simon Singh, The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography, 1999: 10)

Singh’s description of della Porta’s recipe only appears in the first edition of The Code Book. In later editions it is missing without comment. The reason might be found by reading della Porta himself, who in Book 16 chapter 4 of his Natural Magic mentions the technique, but neither claims to have invented it nor to have gotten it to work:

“Africanus teaches thus: ‘grind [oak] galls and alum with vinegar, until they have the viscosity of ink. With it, inscribe whatever you want on the egg and once the writing has been dried by the sun, place the egg in sharp brine, and having dried it, cook it, peel, and you will find the inscription.’ I put it in vinegar and nothing happened, unless by ‘brine’, he meant sharp lye, what’s normally called capitellum” (della Porta, Magia Naturalis 16.4: Latin 1590, English 1658)

Della Porta attributes the recipe to Africanus, probably Sextus Julius Africanus, a 2nd–3rd century CE traveler, writer and chronicler, whose recipe for an egg-permeating ink is preserved in the 10th century Greek compilation known as the Geoponica, of which della Porta’s recipe is a literal Latin translation. Unlike Singh’s or Nagy’s recipe, della Porta’s includes oak gall (an ingredient often found in inks as a pigment) and lacks precise measurements.

The measurements and techniques described by Singh seem similar to a recipe printed on page 143 of the 1973 New Earth Catalogue (Figures 2 and 3):

Figure 2: The New Earth Catalogue: Living Here and Now, ed. Scott French and Gnu Publishing, New York: Putnam Berkley Press, 1973. Image via MareMagnum.

Writing Under Shell of an Egg. Dissolve one ounce of alum in a half pint of vinegar and use a small brush to paint whatever you wish to appear on the shell of an egg. After he egg has dried completely, boil it for 15 minutes [...].
Figure 3: P. 143 (detail, via Google Books Snippet View) of The New Earth Catalog: Living Here and Now.
This recipe uses half the amount of vinegar. It also mentions that a small brush is to be used and says to boil the egg for 15 minutes. None of these details are in Singh’s or in della Porta’s version.

This recipe shares a strong family resemblance to a one published by the USDA in 1965, whose purpose was to get children to eat more eggs. We know this because the USDA’s suggestion was picked up by the New York Times and published on page 14 of the 29 May 1965 issue (Figure 4):

Mess on an Egg is Tempting to Child. To increase a child's consumption of eggs, us "invisible writing," the United States Department of Agriculture suggests. Secret messages can be painted on the outer shell of eggs before they are hard-cooked, and nothing will be visible until the egg is cooked and the shell removed. The message will be on the hard-cooked egg white. To make the "magic ink," dissolve one ounce of alum (available in drugstores) in one cup of vinegar. Use a small pointed brush to write on the shell. Let it dry thoroughly and then cook the eggs in simmering water for about 15 minutes. Cool quickly.
Figure 4: P. 14 (detail) of 29 May 1965 New York Times with an invisible ink recipe attributed to the USDA.

Sometime between 10 and 20 years earlier, either in 1946 or 1959, a similar version similarly targeted to children was published in volume 14 of Richards Topical Encyclopedia, an encyclopedia ordered by theme that was sold door to door in the US (Figure 5).

The Warning Beneath the Egg Shell. Mix an ounce of alum with a half pint of vinegar. Then with a fine brush, using the mixture as an ink, write a message--a joke, a prophecy, anything you like--on the shell of an egg. After the egg is boiled in water for about fifteen minutes, the writing will disappear, but your unsuspecting friend who removes the shell will find the message on the hard-boiled egg inside.
Figure 5: P. 136 (detail) of volume 14 of Richards Topical Encyclopedia, published either in 1946 or 1959.

Another 10 (or 20) years before that, we find the recipe on page 58 and 132 of the February 1936 issue of American Druggist. A reader from Oregon asks for the recipe of a solution used to mark eggs. The editor replies that the “trick” is described ‘in Henley’s “Book of Recipes”.’ (Figure 6)

Egg Shell Marking. "Oregon" used to mark eggs with a mixture of brown sugar syrup and some acid. He has forgotten the formula. The trick, as described in Henley's "Book of Recipes" is as follows: (Continued on page 132) Notes and Queries...continued from page 58. Dissolve an ounce of alum in 8 ounces of vinegar and use the solution to "write" upon the egg, using a small pointed camel's hair brush. Dry the egg and boil it for about 15 minutes. By that time the markings on the shell will have disappeared but when the shell is removed the writing will appear on the hardboiled white of the egg.
Figure 6: P. 58 and 132 (detail) of February 1936 issue of American Druggist.

The editor’s recipe is not obviously the one “Oregon” was after (it includes neither sugar nor acid) but the details are familiar: 1 oz alum, 8 oz (= 1 cup = 1/2 pint) vinegar, a small, pointed brush, 15 minutes boiling. Some details are new: we’re told the brush should be camel’s hair (I will come back to this in the sequel).

The editor of American Druggist also gives a source: Henley’s “Book of Recipes”. The Norman W. Henley Publishing company was active in the United States in the early 20th century and beginning in 1907 published almost yearly editions of an extremely popular book of household recipes: Henley’s Twentieth Century Book of Recipes, Formulas and Processes: Containing Nearly Ten Thousand Selected Scientific, Chemical, Technical and Household Recipes, Formulas and Processes for Use in the Laboratory, the Office, the Workshop and in the Home By Gardner D. Hiscox.

I checked the 1907 edition of Henley’s, but found nothing. I continued looking for references to the recipe closer in time to the American Druggist issue to refine the search. I found two earlier instances: page 97 of the January 1930 issue of Popular Science, and (slightly earlier) page 110 of the September 1929 issue of Field and Stream, where it is referred to as ‘an old hex trick’ (Figures 7 and 8):

Making Writing Appear on Whites of Boiled Eggs. An easy and effective trick is to letter a prophecy on the shell of an egg, using a mixture of an ounce of alum in a half pint of vinegar as the medium and applying it with a fine brush. Place the egg in water and boil for about fifteen minutes. The lettering on the shell will disappear, but on removing the shell, the prophecy will be seen on the hard-boiled white of the egg.
Figure 7: P. 97 (detail) of January 1930 issue of Popular Science.
1001 Outdoor Questions. By Iroquois Dahl. Ques. Not long ago I saw the egg of a domestic hen boiled, and when cracked and opened, the following words and figures appeared, perfectly printed on the white of the egg: “Ware will come in 1932.” As I am a disbeliever in hokum and bunk, I would appreciate information on how this was done? Ans. This sounds like an old hex trick. You can write on the inside of an egg by dissolving 1 ounce of alum in ½ pint of vinegar. With a small pointed brush, outline whatever you writing you desire on the shell of the egg with this solution. After the writing has dried thoroughly, boil the egg for 15 minutes. All trace of writing should disappear from the shell, and when the egg is cracked and shelled, the writing will appear on the hard-boiled white.
Figure 8: 1985 reprint of p. 110 of September 1929 issue of Field and Stream.

If Henley’s was the ultimate source, the recipe had to have appeared sometime before 1929. I checked the 1925 edition, but it was nowhere to be found. The next edition was published in 1929, the same years as the Field and Stream recipe. There it was on page 786 (Figures 9 and 10):

Wood Polishes; Wood Renovators; Wood, Securing Metals To; Wood, Waterproofing; Wood’s Metal; Wool Fat; Worm Powder for Stock; Writing, Restoring Faded […].
Figure 9: P. 786 (detail) of Henley’s, the 1925 edition. No recipe.
Wood Polishes; Writing Under the Shell of An Egg: Dissolve one ounce of alum in a half pint of vinegar with a small pointed brush outline whatever writing you desire on the shell of the egg with the above solution. After the solution has dried thoroughly on the egg, boil it for about 15 minutes. If these directions are carried out all tracings of the writing will have disappeared from the outside of the shell--but when the shell is cracked open the writing will plainly show on the white of the egg.
Figure 10: P. 786 (detail) of Henley’s, the 1929 edition, with the earliest version the author could find of this recipe.

The recipe contains many of the characteristics of the one that has been passed down in American lore and attributed in one form or another to George Washington’s spies or Giambattista della Porta: 1 oz. alum, ½ pint vinegar, a small brush, 15 minutes of boiling.

Given the reach of Henley’s “Book of Recipes” in the US, this is not surprising. But Henley’s recipe also lacks a key ingredient from the recipe that della Porta attributed to Africanus: oak gall. How and when this ingredient dropped out from a recipe reliably passed down for over a thousand years is another story.


This post continues a study of how a 3rd century recipe for a magic ink, despite the fact that it probably never worked, still managed to work its way into American popular culture in the 20th and 21st centuries. An earlier part of the study is posted here.

 

A valuable ancient commodity: Miltos of Kea

By Effie Photos-Jones

The island of Kea in the North Cyclades is by some travel agents’ reckoning the (rich) Athenians’ ‘best-kept secret’, their beautifully-designed stone-built villas merging seamlessly with the barren landscape overlooking the blue Aegean Sea (Fig 1).

Fig. 1 Private house in Orkos, looking east. To the SE on can see the island of Kythnos. (c) Effie Photos-Jones

The scenery is even more spectacular in the south and in the east of the island. Although sparsely populated today, this area was from the mid of the 19th century and well into the early part of the 20th century, a hive of activity, on account of the extensive underground workings of the seams of lead and iron ores. Today, miners’ cottages stand derelict, perhaps waiting for a buyer to convert them into holiday homes. But the ground underneath Petroussa, Orkos or Trypospilies (Fig 2 map) is riddled with galleries, some dating as early as the 4th century BCE. These early galleries were opened with one aim in mind: to access miltos (Fig. 3c).

Fig. 2. A map of Kea with its four ancient city states and the miltos names Orkos, Petroussa, Trypospilies. (c) Effie Photos-Jones

The material they called miltos is a composite one consisting of naturally fine iron oxides (hematite/goethite) with small amounts of calcite, quartz and clay minerals. It made its first appearance in the Bronze Age Linear B clay tablets  as mi-to-we-sa. The Mycenaeans, acutely aware of colours, had many names for red, miltos being, we think, a red with a deep purple hue. It would be many centuries before Kea miltos would surface again in the literary record, always as the colour red but also as a whole host of materials whose colour merited that name. In the 4th century BCE Theophrastus (On Stones, 52) tells us that builders and joiners used it to draw a line with, workers in shipyards used it for ship maintenance and if the miltos came from the island of Lemnos, then it was used as a medicine, as well, and against ‘poison’.

From the above it is clear that miltos was a valuable commodity. But how valuable? An Athenian decree carved on a marble inscription found in the Athenian Agora and dated c. 360 BCE tells us exactly how valuable. The decree was issued by Athens to all the three city states of Kea (Ioulis, Korisseia and Karthaia (Fig. 2) requiring each one of them to export miltos in its entirety from their respective mines, exclusively to Athens; also for the Keans to bear the charges for the transport and only in an Athenian boat! The tone is severe and the penalties dire. The decree appears to openly invite a slave to denounce his master, if the latter is suspected of selling his miltos to a third party. It stipulates that the slave would be gaining not only his freedom but would also receive half of his masters’ estate!

Another contemporary inscription, more informative than severe, also from Athens mentions miltos mixed with pitch, the miltopissa. And at an even later date (3rd century CE), the author of an agricultural manual, recommends miltos for pest control. It suggests miltos should be smeared around the roots of trees ‘to prevent trees and vines from being harmed by worms or anything else’.

So what was the rationale behind all these diverse uses of miltos? was it a case of ‘since we have it …we might as well use it!’ or did antiquity have a more subtle understanding of this valuable natural material which has so far eluded us? We have been investigating….

As was mentioned miltos consists of very fine iron oxides with particle sizes ranging in the nanosized range. There are also impurities of lead, zinc, copper and arsenic within. But beyond its mineral components, Kean miltos also had an organic load. By that we mean microorganisms like bacteria, fungi and other which live around miltos, are feeding on miltos and also alter the environment around it (Fig 3). We became aware of these microorganisms through DNA sequencing of the miltos samples. Given that red Kean miltos was never heated but used in the ‘as was’ state it is almost certain that these microorganisms would have been carried along with the minerals. When the microorganisms died, they would release biomolecules (secondary metabolites), many of which are known to have numerous beneficial properties, as antibacterials, antifungals, antioxidants or other.

The diagram below (Fig. 4) gives a schematic illustration of the dual nature of Kean miltos, as a combination of both a biotic (microorganisms and biomolecules) and an abiotic (elements, nanoparticles, minerals) component.  It is the ‘intersection’ between the two components that gives rise to miltos’ diverse applications.

Fig. 4. Miltos’ diverse properties deriving from their biotic and abiotic components. (c) Effie Photos-Jones

When miltos is mixed with resin or pitch and applied on wood it is the toxic trace elements within which would inhibit the growth of deleterious biofilms. The same mixture could be used as pest control, by preventing the growth of microorganisms/ insects threatening tree health. If on the other hand, when miltos was mixed with water, the toxic trace elements within, mostly insoluble, would have little effect. Instead, it would be its biome, in the shape of bacteria which help the growth of plants, by making nutrients bioavailable at the root level, which would render miltos a good fertiliser. In short, each application appears, to have called upon and with confidence, either the biotic or abiotic component of miltos depending on the ‘problem’ at hand. No wonder the Athenians were taking no chances with the Keans and their miltos.

We have for long considered miltos a good and ‘special’ red pigment. But all along, it has been way more than that. The Athenians had made a shrewd assessment of this natural material and as an all-powerful city state they imposed their might on their allies. With the demise of the Athenian hegemony in the region, the importance of Kean miltos faded only to give prominence to that of Cappadocia traded through its Black Sea port of Sinope (Sinopic miltos).


Further Reading

Lytle, E. (2013). Farmers Into Sailors: Ship Maintenance, Greek Agriculture, and the Athenian Monopoly on Kean Ruddle (IG II 2 1128). Greek, Roman, and Byzantine Studies, 53(3), 520-550.

Photos-Jones, E., Cottier, A., Hall, A. J., & Mendoni, L. G. (1997). Kean Miltos: The well-known iron oxides of antiquity. The Annual of the British School at Athens, 92, 359-371.

Photos-Jones, E. et al. (2018). Greco-Roman mineral (litho) therapeutics and their relationship to their microbiome: The case of the red pigment miltos. Journal of Archaeological Science: Reports, 22, 179-192.


Effie Photos-Jones

Glasgow, UK

EPJ is a Senior Honorary Researcher at the University of Glasgow at the Schools of Humanities and of Earth and Geographical Sciences. She has been researching the metals and industrial minerals of the Greco-Roman world for over 40 years and more recently their pharmacological applications

 

 

 

 

 

 

 

 

 

 

 

Cherries Galore in a Cesspit

By Merit Hondelink

As an archaeobotanist, an archaeologist specialised in studying plant remains found in archaeological excavations, I aim to reconstruct and interpret the relationships between humans and plants in the past. Archaeological plant remains, also known as subfossil plant remains, help us to reconstruct the former landscape and inform us how humans exploited it and even transformed the vegetation. Archaeobotanists do not necessarily study one time period, nor a specific region or topic. They can study plant remains from the Palaeolithic or the 20th century, and everything in between. They can focus on one specific site, work across the country or continent, and even work worldwide. They can delve into topics such as natural vegetation, forestation, domestication, trade, food consumption and much more. The one thing that all of this has in common is the link between humans and plants. But most archaeobotanists do specialize, most notably in the plant parts they study, such as fruits, seeds, pollen, wood or phytoliths. And most archaeobotanists have a beloved time period, favourite region or topic that they find most intriguing. In my case my research focuses on early modern Dutch urban food consumption.

I study what people ate in early modern Dutch cities, and how this changed through time. The best way to study what people ate in the past, is to look at their excrement and kitchen refuse, both of which can be found in the archaeologists treasure trove: the cesspit. These latrines were used to empty one’s bowels, but also served as a place to discard kitchen refuse and household waste. The content of a cesspit consists of organic remains from plants and animals, inorganic (culinary) material culture such as earthenware, glassware and ceramics, but also wooden cups and plates, as well as (decorative) objects, personal belongings and much, much more.

Figure 1: A selection of faunal and floral items found in a late medieval cesspit sample from Groningen. Photo: Dirk Fennema.

The content of an archaeobotanical cesspit sample consists of, among others, floral remains in different shapes and sizes (Figure 1). The items are sorted with the use of a microscope (Figure 2) and identified on a species level (and sometimes even on the level of species variety) by using a reference collection (Figure 3). The Groningen Institute of Archaeology offers a wonderful digital, open access, reference collection, see https://www.plantatlas.eu/.

Figure 2: A peek through the microscope. Visible is a fragment of text and different seeds and fruits, taken from an early modern Delft cesspit sample. Photo: Merit Hondelink.

When the content of a cesspit sample is analysed, sorted and identified, the interpretation begins. What can these plant remains tell us about past human-plant relationships? Most plant species are interpreted in a standardized way: wild plants inform us about the vegetation composition, make-up of soils and hydrology, whilst agricultural weeds in particular inform us about the crops grown and their local, regional, international or even global provenance. Wild but poisonous or toxic plants inform us about potential medicinal applications. A majority of plant species found in cesspits are classified as economic plants, grown as a food crop or cultivated for other useful purposes, such as fibres for textiles or seeds for oil. Identifying edible plants helps us better understand what plants people used for food and which parts people consumed. It also helps us better understand how food was prepared in the past, as preparation marks can be left behind on seeds and fruits.

Some preparation marks are easier to identify than others: nuts need to be cracked to get to the seed; apple seeds may be sliced when cutting up an apple, cereals can be ground, resulting into fragmented bran. But sometimes the archaeobotanist finds fragmented plant parts that, at a first glance, do not make sense.

Figure 3: A small selection of the tubes from the archaeobotany reference collection housed at the Groningen Institute of Archaeology (GIA) at the University of Groningen. Photo via GIA.

I have come across dozens and sometimes hundreds (or even more) cherry stones and plum stones in a single cesspit sample. No surprise there, cherries and plums were grown in local orchards, sold in the market and consumed with gusto. Most of these stones will have been discarded in the cesspit as a result from eating the fruits and spitting out the stones, or after de-pitting the fruits for dinner preparation. Only a small percentage is assumed to have been accidentally swallowed and secreted as excrement. Still, archaeobotanists find many fragments of cherry and plum stones (Figure 4). This is something that raises questions when you think about it. Why would these sturdy fruit stones be fragmented? A more pressing question when you are aware that the Rosaceae family, among others also including almond, peach, and even apple, contains – to varying degrees – hydrocyanic acid, also known as hydrogen cyanide and sometimes called prussic acid. The seed coat and fruit wall protects the consumer from digesting this acid, which can be poisonous when consumed. So why would someone break the stones of these fruits?

Figure 4: Two fragments of cherry stones found in an early modern cesspit in Vlissingen. Photo: Merit Hondelink.

To test the assumption that cherry stones were fragmented intentionally, and not through, for instance, pressure, an experiment was devised. Cherries were bought at the farmer’s market and taken to a physics lab to measure the pressure required to fragment the stones. After a number of tests, the calculated force to fragment a cherry stone averaged 23,9 kg or 239 Newton (Graph 1). This makes it more plausible that the stones were intentionally fragmented, as opposed to – for instance – fragmentation due to soil pressure.

Graph 1: Force needed to fragment a cherry stone. On the vertical axis the force (N), on the horizontal axis the elongation (μm). The point where the line falls is the moment the cherry stone breaks (max. force – max. elongation).

Consulting early modern cookbooks provided me with a list of recipes requiring the cook to de-stone cherries for the preparation of jams, sauces, syrups and tarts. Delicious experiments ensued, but I did not manage to fragment cherry stones whilst cutting and de-stoning, pressing through a cloth or colander, or by just baking the fruit with stones in a tart in the oven. Working a batch of cherries with a mortar and pestle did the job, though. But than you would have to pick the fragmented stones from the mushy cherries: not ideal at all. Picking up the eighteenth century encyclopaedia compiled by Noël Chomel gave me the hint I needed. In the Dutch version of his Dictionnaire œconomique (Algemeen huishoudelijk-, natuur-, zedekundig- en konst- woordenboek), he mentions different recipes for preparing cherries. Two recipes for cherry liquor instruct the reader to fragment the cherry stones by using a mortar and pestle (Figure 5). The fragmented fruits, including the stones and (I assume) the seeds are added to the brandy (Dutch: brandewijn) and, after closing the bottle, the mixture is put in the sun to infuse. Adding spices such as cinnamon, cloves and sugar is optional, according to the author.

Figure 5: How to make a pleasant cherry liquor (Noël Chomel, 1778).

So, it is plausible that the fragmented cherry stones found in early modern cesspits are the result of the domestic production of cherry liquor. Other fruits, such as plums and peaches, are also used to make a fruity liquor according to Chomel’s encyclopedia. However, what happens to the acid contained in the seeds? That requires further research. It might be that the prescribed infusing in the sunlight helps denature the acid into harmless molecules, leaving only the (bitter) taste behind. This line of research will be undertaken come summer with the aid of a brewer and some chemical analysis. In the meantime, a cherry and cinnamon flavoured lemonade is my poison of choice. Bottoms up!

A Roman Vegetarian Substitute for Fish Sauce

By Edith Evans

Roman cookery has been one of my research interests since the 1980s; I’ve accumulated a large repertoire of ancient recipes and usually do at least one live demonstration a year.  Most of the recipes include garum or liquamen – fish sauce – as a taste enhancer, providing salt and umami. Whilst finding fish sauce is fairly easy nowadays in Britain (the Romans used the same techniques to make it as the modern Thai and Vietnamese), using it at demonstrations disappoints vegetarians who would otherwise like to sample the plant-based dishes.

I found the answer to this problem in a Late Antique agricultural treatise:

Liquamen from pears: Ritually pure liquamen (liquamen castimoniale) from pears is made like this: Very ripe pears are trodden with salt that has not been crushed. When their flesh has broken down, store it either in small casks or in earthenware vessels lined with pitch. When it is hung up [to drain] after the third month without being pressed on, the flesh of the pears discharges a liquid with a delicious taste but a pastel colour. To counter this, mix in a proportion of dark-coloured wine when you salt the pears.
– Palladius: Opus Agriculturae 3.25.12

Liquamen castimoniale must have been required for people observing certain religious strictures (castimoniale means ‘to do with religious ceremonies’). Why would ordinary liquamen have been thought unsuitable? Was it the fish? (Pliny the Elder writes of a special fish sauce for Jews (Natural History 31.95) that he calls garum castimoniarum, although he’s obviously got the wrong end of the stick when it comes to Jewish food laws because he says it’s made using fish without scales). Alternatively, was it because liquamen was the product of fermentation? Fermentation was often considered a form of decomposition, which might have led it to be regarded as ritually unclean.

This has a bearing on how we interpret the recipe. Although Palladius tells us the ingredients to use (whole pears and salt, plus optional red wine) he does not give any information about the relative proportions. This leaves us with two possible techniques. Either you use a high proportion of salt and effectively create a brine utilising the juice of the pears, or you use a low proportion and promote a lactic fermentation by incubating the mix a suitable temperature (although Palladius doesn’t mention this). When used to flavour food, the product of the first method adds a strong taste of salt but no umami. The second would add some umami but also acidity, but a much lower amount of salt. However, if the problem was the fermentation itself, the second method would have been as unacceptable as standard fish sauce.

I’ve had a go at the lactic fermentation method, using 2% of the weight of the pears in salt, but when I tried it, the mix went mouldy before fermentation had a chance to take hold.  I’ve had much more success with the first method and have repeated it enough times to get a consistent product. The best pears to use are juicy varieties with very tannic skins, like Williams (also known as Bartlett) and Comice. I mash up the pears – stalks, skins, cores and all – mix them with 25% – 50% of their weight in coarse sea salt (I don’t bother with the wine), and leave them at the back of the fridge in a glass jar with the lid only lightly screwed on. At the end of two months (unlike us, the Romans counted inclusively), the pulp has started to separate out. The heavier elements form a pale layer at the bottom of the jar, whilst the top part of the mixture is more liquid and is a pale pinkish-brown. When drained through a nylon sieve, the colour of the resulting liquid is a very pale version of the colour of fish sauce. 

I’ve tried various proportions of salt, and found that, if you use 50%, you seem to get more liquid, probably because the mixture doesn’t draw in moisture from the air to the same extent.  But a smaller percentage of salt allows more of the delightful pear flavour comes through – I find it much more difficult to detect in the 50% version. Stored in a clean bottle it will keep for months without refrigeration.

Figure 1: The pear liqumen is in the flask with dark blue trim

I’ve only had a problem once, when spots of mould had appeared on the surface of a batch six months after I’d made it. As I was due to give a Roman cookery demonstration in a few days’ time I had to quickly rustle up something I could use, so I cored and cut up a pear, boiled it with 25% salt and a little water, removed the peel and pulped the flesh in the blender. It was much too pale, but the taste was the same and I decided it would be a useful method for someone who couldn’t wait two months – in fact that’s what I recommend for my Roman Cookery School videos (https://m.youtube.com/user/GGATArchaeology and https://en-gb.facebook.com/GGATarchaeology/).