Many historical mead recipes ask for a wort 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.
This instruction to determine density does not appear in the Roman-era or medieval recipes I have. It first appears in a French recipe for mead in 1576 (Estienne, 1576) “they take the knowledge that it is cooked by an egg that they throw in; which if it swims over it is a sign that it is cooked, if it goes to the bottom, it is not cooked.”. The instruction to float an egg appears again in mead recipes from a Dutch beekeeping book (Clutium, 1619), and again in multiple 17th century recipes.
The problem is reasonably straightforward when we use science. Note: although there are always caveats and ifs, 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, lead is 19.32, and pure alcohol is 0.789.
To answer the question at hand there are three issue toresolve in sequence:
- What is the density of a fresh laid egg.
- What does it mean that the egg floats or a certain amount of it is above the water?
- What factors complicate the situation that need to be taken into account?
What is the density of an egg?
Hoff, 2017 in an internet article ‘What is the Density of an Egg?’ nicely summarizes this question. Hoff says that according to the Nova Scotia Dept of Agriculture the density of an egg decreases over time as air enters through the shell. 1.033 is cited as the density of the contents of fresh hen egg from a 1949 study; since whole eggs are of interst, this data does not help. Another 1982 article is cited; initial egg density from 23 species ranged from 1.055-1.104.
A third reference leads to ‘The Avian Egg’ (Paganelli, 1974) This paper uses data from over 20 bird species toderive an equation for egg density. Density = 1.038 x egg weight (gm)^0.006. Their sample of 12 domestic chicken eggs had an average initial weight of 53.9 grams. These averages give a density of 1.063 using their equation.
Typical weights for modern hen eggs are 50 gm for a medium hen egg and 57gm for a large egg gives a bulk density of 1.062 and 1.063 respectively. If a small egg of 40 grams is assumed, density is 1.061.
Based on this I’ve chosen 1.062 as the density for a whole hen egg. When freshly laid.
Using Egg Density to Derive Specific or Initial gravity
If an egg in a honey/water solution being prepared to make mead is neutrally bouyant, the mixture is also 1.062 gravity, this is equivalent 1.35 lb/gal sugars, 1.7 lb/gal honey, alcohol potential about 8%.
But typical recipe instructions have the egg float, often to a certain height above the water, implying additional buoyancy beyond neutral.
If 2% of the egg volume is above the water: SG is about 1.085. 1.85 lb/gal sugar, 2.3 lb.gal honey. 11-12% alcohol.
If 5% of the egg is above the water, gravity about 1.115. 2.5 lb/gal sugar, 3.1 lb/gal honey, 15-16% potential alcohol. 1 part honey to 3 parts water in wort. This is notably a pretty common ratio in historical recipes.
Another complicating factor is that the egg buoyancy is typically measured while the wort is heated or boiling. Considering that with 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). A gravity of 1.063 at boiling (where the egg is neutrally buoyant) goes to 1.11 at room temp. The 1.085 at 2% of the total egg volume exposed at boiling becomes 1.13 at room temp. This 1.11 to 1.13 gravity is 3 to 3.5 pounds per gallon honey, a range that is perfect for wine strength semi sweet to sweet mead.
The question of correlating specific diameters of an egg showing above water – how much egg is really above water at the breadth of a groat is important to refine the calculation. Results will be posted when the calculations have been carried out.
BIBLIOGRAPHY
Clutium, Theodorum. 1619. Van de Byen Hare wonderlicke Oorsprone. Utrecht.
Google Books
In Dutch. On Bees. Mead recipes.
Estienne, Charles & Liebault, Jean. (1576). Maision Rustique. Paris
http://reader.digitale-sammlungen.de/en/fs1/object/display/bsb10165012_00007.html
How to run a large farm and use the products from it.
Paganelli, C.V., A. Oloszowka, A. Ar. 1974. The Avian Egg: Surface Area, Volume, and Density. The Condor: 76: 319-325.
Information on egg density.
Last Updated June 19, 2018
