bearing an egg
bearing an Egg
Many historical mead recipes ask for a must than can ‘bear an egg’, or ‘make an egg float’, or ‘bear an egg the breadth of a groat’.When specified, a fresh laid egg is usually desired.
What does this mean in terms of how much honey/ sugar is in a mixture?
The first known appearance of this instruction in a mead recipe is in an English metheglin recipe scribed in about 1444 – “it is myghty enough if it ber an eye that thow may see a peny brede of the ey above the water” (Wellcome MS.MSL.136., before 1444, f.22v), A later French recipe 1576, Germany in 1573, and the Netherlands in 1597. The instructions becomes somewhat common, appearing in multiple 17th century recipes.
That an egg will float in a brine solution was known by the 10th century at the latest, and I believe much earlier (another detail to track down).
The problem seems reasonably straightforward when we use science. Note that although there are always complicating factors, for our purposes SG = specific gravity = density = grams per cubic centimeter gm/cm^3. For those unfamiliar with density, it is a measure of mass per unit volume: water is 1.00, honey is about 1.4, lead is 19.32, and pure alcohol is 0.789.
To answer the question at hand there are three issues to resolve in sequence: 1. What is the density of a fresh laid egg? 2. What does it mean that the egg floats or a certain amount of it is above the water? 3. What factors complicate the situation that need to be considered?
What is the density of an egg?
A 1923 study of almost 1000 hens eggs showed that over 95% had a specific gravity between 1.05 and 1.09 (Mussehl, 1923). A 2023 study limited to modern laying hens of a single species tested over 6000 eggs typically weighing between 55 and 63 grams, and showed a much tighter and higher range of gravities, of about 1.085 to 1.095 (Olivera-Boreli, et. Al., 2023).
This specific gravity is linked to breed of hen, size of egg, age of hen, time of day an egg is laid, diet for the hen, time since laying, and a host of other factors. But a key factor is egg shell thickness, because the shell is by far denser than the remainder of the egg, so a small change in the relative amount of shell has a relatively large effect on specific gravity. In this case the earlier results are probably more representative of medieval eggs, the newer ones representing a monoculture selected for larger eggs with thicker, more durable shells for modern processing and sale.
That medieval eggs were likely to be highly variable in density is confirmed by a less rigorous study of 15 eggs from 4 breeds of hens I conducted which showed just-laid specific gravities of the eggs varied from 1.057 to 1.088. This range appears to be representative; a range of gravities of 1.055 or 1.06 to 1.085 or 1.09 translates to a difference in alcohol potential of about 4%.
Using Egg Density to Derive Specific or Initial gravity
Typical recipe instructions have the egg float, often to a certain height above the water, implying additional buoyancy beyond neutral. The more that floats, the greater the gravity required to lift the weight above the surface.
Another complicating factor is that the egg buoyancy is typically measured while the must is heated or boiling. In active boiling, the agitation of boiling will make it difficult to observe how much an egg floats, I think it is safe to assume the liquid will be taken off boil long enough to measure in a still liquid.
Boiling water has a density of 0.958, but the denser honey in the boiling water will also increase the density of the boiling honey:water mixture. I could not readily find good data on honey density at higher temperatures, so I’ve decided to assume that the density decrease in honey is proportional to that of water (which is probably not true, but the error is quite small relative to both the total numbers and the other sources of variation in brewing results). The egg being added is going to have its usual density.
A gravity of 1.063 at boiling (where a specific egg is neutrally buoyant) goes to 1.11 at room temp.
What does this Mean?
It means the egg float test is a relatively poor way to get a precise measurement of gravity of mead must (or any other liquid)
BUT …
The range of gravities represented by eggs floating in must, ranges from a low density egg just floating at perhaps 1.05 to 1.06 OG to a dense egg measured while the liquid is just off boiling and with some amount showing above the water – perhaps 1.12 or even 1.14 OG.
AND …
A range of 1.055 to 1.14 OG is a remarkable match to the range of OGs typical for mead making. The lower end will make a lower alcohol, drier mead, still near the top of the range modern competitions consider “hydromel”. The higher end will produce a strong mead that likely has a fair amount of residual sugar.
In other words, while the precision of the egg float test is scientifically poor, its application is almost certain to produce a must that can produce a mead well with alcohol and sweetness ranges expected by both historical and modern brewers.
BIBLIOGRAPHY
Clutium, Theodorum. 1619. Van de Byen Hare wonderlicke Oorsprone. Utrecht.
Estienne, Charles & Liebault, Jean. (1576). Maision Rustique. Parishttp://reader.digitale-sammlungen.de/en/fs1/object/display/bsb10165012_00007.html
Mussehl, F. E. 1923. Influence of the specific gravity of hens’ eggs on fertility, hatching power, and growth of chicks. Journal of Agricultural research. Vol.XXIII, No.9 pp.717-720. https://naldc.nal.usda.gov/download/IND43966636/PDF
Olivera-Boreli, F. P. de, Pereira, D. P., Alencar Gonçalves, J., Silva, V. Z. da, & Alencar Nääs, I. de. (2023). Non-destructive assessment of hens' eggs quality using image analysis and machine learning. Smart Agricultural Technology. Volume 4 100161, https://doi.org/10.1016/j.atech.2022.100161
Last Updated August 16, 2023
Last Updated August 16, 2023
