The Egg Float Test explained, for period Soapmakers, Cooks, and Brewers.
By Unnr in elska á Fjárfella (Susan Verberg, 2017).
Sometime in the middle of the 16th century someone figured out that a fresh laid chicken egg has a similar density as certain strengths of solutions. The egg will float instead of sink as it would in plain water, indicating a specific strength or density. First mentioned in soap making manuals to check the strength of lye (1558), it quickly surfaced both in cooking recipes to check the strength of brine (1597), a solution of salt & water, and brewing recipes to check the strength of must (1594), a solution of fruit or honey sugars & water.
Initially the only available references for the egg test in brewing were from the copious but out of period 1669 cookbook The Closet of the Eminently Learned Sir Kenelme Digby Knight Opened. Even though this manuscript came from Digby’s lifelong collection of recipes and was posthumously published several years after his death so could be seen as probably period, his recipes are much more contemporary to 17th century recipes than to what is found before. For instance, many recipes mentioned in Digby use ingredients and techniques not yet found, or commonly used, in our period of study. The addition of citrus, like lemons, and the use of raisins, which is common in Digby, is not found in any of the pre 1600 recipes. And the technique of aging in the bottle, often for a sparkling beverage, is something that does not match with the medieval method of serving mead young or aging in wooden casks and barrels either. But even though the recipes themselves may not be period, they do tend to include more information on the actual process and can serve as a good almost period explanation on previously unexplained techniques.
It was not until I delved deeper into period mead making that I came across four late 16th century brewing recipes mentioning the egg float test, and was finally able to firmly place this technique within our time of study for all three crafts: soap making, cooking and brewing. This article explores the underlying process and easy application of this intriguing trick of science!
But doesn’t a floating egg mean the egg is spoiled? It depends. The floating egg technique works by way of the internal design of an egg, which includes an air sack at the rounded end of the egg for the bird embryo to breath. A fresh egg has a relatively small air sack but as the egg shell is slightly porous over time the size of the air sack increases as the contents of the egg slowly evaporate and dry out. As an old egg will have a large air sack, when put into water it will bob up and float. This test is still used in our modern times to test to see if an egg is fit to eat before cracking it and not be surprised with a sulfur bomb!
Because the size of the air sack changes over time, interfering with the results of our density test, it is very important to use a fresh egg which has not yet had time to evaporate. It is also important to check the supposedly fresh egg as eggs sold in the supermarket are not always as fresh as you might assume (check the sell by dates or even better, get a local backyard egg). To do this, before every density test calibrate your egg in plain water to make sure it sinks flat to the bottom, with both butt and tip level. Use a wide mouth glass jar and tongs to place the egg on the bottom as it can sink so fast it cracks in bigger jars.
The density or specific gravity of water is 1. When minerals like salts or sugars are dissolved into water the extra particles change the density of the solution by making it more crowded, or dense. A fresh egg has a density between 1.03-1.1 g/ml which means it would be borne, or float, by a solution of a density matching or exceeding 1.03-1.1 g/ml. A saturated salt solution, or brine, has a density of about 1.2 g/ml, a wood ash lye solution for laundry soap a density of about 1.11 g/ml and a brewing solution would be between 1.06-1.1 g/ml – all fairly close together and why using the egg test works, in some way or another, for all three.
In modern brewing a hydrometer is used to take a starting (before fermentation) and finishing (after fermentation) gravity reading. Determining the difference of sugars between start and end makes it possible to calculate the percentage of alcohol produced by the yeast from that difference (what is gone has been consumed by the yeast and thus converted into alcohol). As medieval brewers were not aware of the micro-biology involved in brewing and artificially stopping the yeast for a specific alcohol content was not understood (how they wished to know what caused the summer ‘boiling’ and consequent explosions of wine!), all the brewer needed to know was if there was the right amount of sugar for proper fermentation.
Most recipes ask for so many pounds of honey to so much water, why should you go through the trouble of checking the density to make must? For two reasons, the first being that not all honey is created equal. A thick syrupy honey created in a dry year will have more sugar per liquid volume than a thin, runny honey. Both will make mead, but if you measured a thin honey to make sweet mead you might be unpleasantly surprised at the dry white wine-like mead you ended up with… Secondly, in period all honey would have been used for brewing, not just the easy to extract. The centrifuge type honey extruder is a modern convenience and allows for high yield with minimal processing. In period honey would be extracted by hand, first by breaking up the combs to leak out as much as they could, and then by washing the broken up combs in warm water to dissolve the remaining and any crystallized honey. This honey/water mixture would be of unknown strength and would have to be checked before brewing, as not enough fermentable sugars could result in an easily spoiled brew and too much sugar can inhibit yeast growth, stalling fermentation and giving competitors a change. I don’t doubt master brewers of the time could eyeball or taste and have a perfect brew each time, but for the less initiated household brewer (and modern re-enactor) it is nice to be able to check with a visual aide, as the Digby recipe Mr. Pierce’s Excellent White Metheglin confirms:
“When it is blood-warm, put the honey to it, about one part, to four of water; but because this doth not determine the proportions exactly (for some honey will make it stronger then other) you must do that by bearing up an Egge.”
Would any kind of fresh egg work? Not until the Digby recipe Mr. Corsellises Antwerp Meath did a recipe specify that the egg should be a hen’s egg “as above, an Hens Egge may swim with the point upwards”. Even so, with differences in breed, health, age and diet the egg size & shape can differ as well. For the best results, Digby’s Mr. Pierce’s recipe advises to test several eggs and pick out the most average one, both in freshness and shape.
“… and put a good number, (ten or twelve) New-laid-eggs into it, and as round ones as may be; For long ones will deceive you in the swiming; and stale ones, being lighter then new, will emerge out of the Liquor, the breadth of a sixpence, when new ones will not a groats-breadth. Therefore you take many, that you make a medium of their several emergings; unless you be certain, that they which you use, are immediately then laid and very round.”
But what does “beare an egge” mean? How does that look like? It depends on the density you’re looking for and the solution you are playing with. For instance, in soap making two densities are used; a strong one to make laundry soap and a weaker one to make body soap. While in the laundry soap recipe the egg is floating horizontally at the surface (with about the size of a quarter above the surface), as the The seconde part of the Secretes of Master Alexis of Piemont of 1560 puts “the Egge into it, and whiles the egge remaineth aboue”; the body soap recipe for shampoo uses “stronge lye that will beare an egge swimminge betwene two waters”, or, the egg is suspended in the middle.
Soapmaking lye looks like: laundry strength lye, and shampoo strength lye.
This shampoo recipe is the earliest sample I’ve found of the egg float density test and is part of the 1558 manuscript The secretes of the reuerende Maister Alexis of Piemount Containyng excellent remedies against diuers disease by Girolamo Ruscelli.
”A very exquisite soap, made of diverse things.
Take aluminis catini (burnt cream of tartar), quicklime one part, strong lye that will suspend and egg in the middle, three pottels, a pot of common oil; mix all well together, put into it the white of an egg well beaten (dispersant), and a dishful of wheat flour (thickener), and an ounce of roman vitriol (cupric sulfate), or red lead (lead oxide pigment) well beaten into powder, an mix continuously for the space of three hours, then let it rest, by the space of a day, and it will be right and perfect. Finally, take it out, and cut it in pieces: afterwards set it to dry two days, in the wind, but not in the sun. Always use this soap, when you want to wash your hair, for it is very wholesome, and makes fair hair.” (Translated by Susan Verberg)
As the density of a saturated salt solution is fairly strong, the egg in a salt solution would also float horizontally at the surface, similar to laundry soap strength lye. The recipe in the 1597 cookbook The second part of the good hus-wiues iewell by Thomas Dawson uses this technique to make sure the brine is saturated and is the earliest mention I’ve found of the egg float test in a cookbook. Apparently, it is also used for numerous pickling recipes of the new world colonies but I have not found any period mentions of that as of yet.
”To keepe lard in season.
Cut your lard in faire peeces, and salt it well with white salte, euery péece with your hand, and lay it in a close vessel then take faire running water, and much white salt in it, to make it brine, the~ boile it vntill it beare an Egge, then put it into your Lard and keepe it close.”
Like with soap, brewing with different sugar strengths makes for different types of brews. The stronger the mead the longer it can keep, as Digby’s To Make Metheglin advises: “If you would have it to drink within two or three months, let it be no stronger then to bear an Egg to the top of the water. If you would have it keep six months, or longer, before you drink it, let it bear up the Egg the breadth of two pence above the water. This is the surer way to proportion your honey then by measure.” Medieval meads are usually fermented using ale yeast, which generally dies off once the alcohol level reaches about 10%. As an alcohol level of about 10-12% will kill off most contaminants responsible for spoiling meads and fruit wines, a higher starting sugar level resulting in a higher alcohol percentage would therefore allow the mead to keep longer. Unlike the soap & brine recipes, the brewing egg does not float horizontal but vertical, as Digby’s Mr. Corsellises Antwerp Meath mentions “so strong that an Egge may swim in it with the end upwards”, indicating an intermediate strength between suspended and floating.
Both the soap making recipes and the brine recipes indicate to boil first, then measure – the brewing recipes are not so certain and often recommend to test the strength before boiling, as Digby’s To Make Metheglin shows: “And the time of the tryal of the strength is, when you incorporate the honey and water together, before the boiling of it.” apparently not realizing boiling evaporates water thereby changing the density. The recipes can also not quite make up their mind if the must should be cold, blood warm or boiling, which could indicate they did not understand how temperature affects specific gravity either, as shown in the 1597 Dutch beekeeping manual “Van de Byen” by Theodorus Clutius; “and let it cook / until an Egg can float in the liquid / then set it off the fire”, which could also resulted in a nicely boiled egg if the egg is not removed… As medieval recipes over many disciplines have a tendency to be brief to the point of missing pertinent information, it is entirely possible the period brewer knew to remove the egg and cool down the must, but did not bother to note that down. The 1616 Danish cookbook Koge Bog advises to “put an egg or two into this lukewarm brew so that there is a part of egg as big as a 2 shilling over the water then it is sweet and fat enough” which probably is the most accurate measurement.
Following are two 16th century recipes which specifically mention using the egg float test:
Jewell House of Art and Nature by Hugh Platt, 1594.
76 A receipt for the making of an artificiall Malmesey.
Take four gallons of conduit water, into the which put one gallon of good English honie, stirre the honie well till it be dissolved in the water, set this water in a copper pan upon a gentle fire, & as there ariseth any skumme take it off with a goose wing or a Skimmer, and when it hath simpered about an hour, then put in a new laid egge into the water, which will sinke presentlie, then continue your first fire without any great encrease, and also your skimming so long as any skim doth arise, and when this egge beginneth to floate aloft and sinketh no more, then put in another new laide egge, which wil sinke likewise, & when that second egge doth also swim aloft with the fyrst egge, let the water continue on the fyre a Paternoster while, then take it off, and beeing colde, put the same into some roundelet, fylling the roundelet brimful. And in the middest of this roudelet hand a bagge, wherein first put some reasonable weight or peize, and to everie eight gallons of liquor two nutmegges groselie beaten, twentie Cloves, a rase or two of Ginger, and a sticke of Cynamon of a fynger length. Set your roundelet in the sunne, in some hot Leades or other place, where the sunne shineth continuallie for three whole monethes, covering the bung-hole from the raine, and now and then fylling it uppe with more of the same composition as it wasteth. This I learned of an English traveyler, who advised me to make the same alwaies about the middest of Maie, that it might have 3. hot moneths togither to work it to his ful perfection. […]
“Van de Byen” (Of the Bees) by Theodorus Clutius, 1597
To make mead.
One shall take the rest that stayed in the basket / from the dripping of the raw honey or zeem / and wash it with hot water / so that all the sweetness goes into the water / until you have a tub full or two / or as much as you want: Then put this liquid in the kettle / and let it cook / until an Egg can float in the liquid / then set it off the fire / and pour it into the barrels and let it cool / add some yeast of beer / and set it to rise and work / and althus filling the barrel / so the filthiness may overflow / and when it does not bubble or work / so shall one close up the barrel / and let it rest. This is the way to make mead / some put in a piece of tied cloth some cinnamon / ginger / nutmeg / cloves and similar spices / to give the mead a good taste and scent. (Translated by Susan Verberg)
Between the end of the 16th century and the publishing of Digby’s cookbook a number of mead recipes are found to use a similar egg float technique as described in Digby, but with old-fashioned ingredients and techniques. This is an interesting time of transition, as by the 16th century not only could the average person read, due to cheaper & more extensive trade unusual ingredients like spices, sugar, citrus, chemicals & pigments became available to the common man. It was a time of great exploration, both of the sea and in the mind, not in the least helped by the success of the numerous Books of Secrets, each claiming to expose trade secrets never seen before, which greatly helped to spread knowledge before only accessible to the educated elite. This period of transition shows in the difference between Digby’s work and our time of interest, both in ingredients used and in their often elaborate and detailed explanations.
Numerous recipes in Digby mention the use of coins, like the groat & two pence (most with an average diameter of about 20mm) as a size measurement of the bit of shell sticking above the water surface. This type of measurement seems to become fairly universal in later times as observed in many of the Digby recipes and later in the US Colonial soap making lye measurements which often also specify an area the size of a coin, in this case a quarter. Even though coins are mentioned in the barely out of period 1604 Complete Receipt Books of Ladie Elynor Fettiplace “so strong of honie that it will cover an egg to the breadth of two pence”, and the 1609 The Feminine Monarchie “make it to bear an egge the breath of a groat”, the period recipes do not specify how the egg should float, only that is should.
So after all this, where do you start? With a fresh egg no more than two days old, of the roundest kind, weighing less than or about 2 ounces. Making a brine solution is easiest: add enough salt until it stops dissolving, which means a saturated solution is reached, place the egg, and slowly add water until it floats just as the recipe likes it. To test lye for soap making the egg would be used after the heated evaporated lye is cooled down, which allows for contaminant minerals to settle out of solution and thus not interfere with the remaining solution’s density (for more information on leaching lye and making soft soap see the Bibliography). For brewing, make your honey must first, heat and evaporate as needed, let cool down to blood temperature, and add an egg. If the egg sinks the must is too weak, if it floats close to tipping or tips, the must is too strong. As the 1609 beekeeping manual The Feminine Monarchie instructs: “If the liquor be not strong enough to beare an egge the breath of a two-pēce above it, thē put so much of your course hony into it, as wil give it that strength: or rather, when it is so strong powre in more water (stirring it with the liquor) until the egge sinke.” In other words; if it is too weak, add more honey, stir well to make sure the sugars are completely dissolved, and try again. If too strong, add some water, stir well, and try again. As you can imagine, it is easier to start with too strong a solution and dilute it, than to start with a weak solution and try to incrementally dissolve more sugars into it.
The table below matches egg position with specific gravity, giving us an idea of what to aim for. Egg readings are given for both 10% tolerance yeast (ale yeast) and 12% tolerance yeast. (from The Egg Test)
|mead||start SG||egg||start SG||egg|
|style||10% yeast||reading||12% yeast||reading|
|Dessert||1.1 +||> 20mm||1.2 +||30mm +|
To make sure there is enough sugar for the yeast to feed on, the egg should float. But if it starts to tip over and not reliably float point up anymore, the solution has become too strong with too much honey sugar for the yeast to properly work and fermentation will likely stall. The average range of 1.08 to 1.12 g/ml at which the average, round fresh laid egg floats point up is also the ideal range of sugar content for starting a successful mead. And now that you have everything you need to make a successful solution using medieval techniques, whether it be for soapmaking, cooking or brewing, and are able to properly document it, let the experiments begin!
I would like to express my thanks to Mistress Roheisa le Sarjent from Lochac for her article The Egg Test for Period Brewers and Mead Makers. It proved a great starting point as we’re working from similar sources, and I’m grateful to find the heavy lifting of figuring out egg readings already done. Tak!
Digby, Kenelme. The Closet of the Eminently Learned Sir Kenelme Digby Knight Opened, 1669
The Project Gutenberg EBook of The Closet of Sir Kenelm Digby Knight Opened. Anne MacDonell (ed.), 2005
Sibly, Belinda. The Egg Test for Period Brewers and Mead Makers, 2004, Mistress Roheisa le Sarjent, Cockatrice, May AS 49, p.20-29.
Butler, Charles. The Feminine Monarchie. Oxford: 1609. Transcription by Susan Verberg.
Platt, Hugh. Jewell House of Art and Nature. 1594. London: Peter Short. Transcription by Susan Verberg
Anonymous, Koge Bog: Indeholdendis et hundrede fornødene stycker etc. Kiøbenhaffn (Copenhagen): Aff Salomone Sartorio, 1616.
Krupp, Christina M. & Gillen, Bill. Making Medieval Mead, or Mead Before Digby. The Compleat Anachronist #120. Milpitas: SCA Inc, 2003. (includes the Complete Receipt Books of Ladie Elynor Fettiplace, 1604).
Ruscelli, Girolamo. The secretes of the reuerende Maister Alexis of Piemount. London: John Kingstone, 1558.
Ruscelli, Girolamo. The seconde part of the Secretes of Master Alexis of Piemont. London: John Kyndon, 1560.
Dawson, Thomas. The second part of the good hus-wiues iewell, London: E. Allde for Edward, 1597.
Clutium, Theodorum Van de Byen. Leyden: Jan Claesz van Dorp, Inde Vergulde Son, 1597. Transcription by Susan Verberg.
More information on leaching soapmaking lye
More information on making medieval soft soap:
More information on brewing with honey: Of Hony, a Collection of Medieval Brewing Recipes. WEBSITE forthcoming…
To find a groat, and other period coins
Image of fresh egg test
Photographs of soap making lye by Susan Verberg, 2016.
Bees coming out of a hive to drive off an intruder. Museum Meermanno, MMW, 10 B 25, Folio 37r –
“Dryckeslag, Nordisk familjebok” from Historia de gentibus septentrionalibus, by Olaus Magnus, Rome, 1555.
See Elska’s blog here.