Molar
mass M
(g/mol)
Density
d
(d-1)/d Molar
volume
(L/mol)
(= M/d)
Sugar 180 1,55
0,355
0,116
Water 18 1 0 0,018
Alcohol 46 0,79
-0,2595
0,058
Honey 1,41
0,2908

CO
2

(gas)
44 0,0018
-554,6 24
Table 8: some properties of sugar, alcohol, etc.
One can notice that
96
,
1
2M
M
a
s and
95
,
1
d
d
a
s .
So
1
M
2M
d
d
s
a
a
s
, that is the volume
y
1
M
2M
d
d
d
M
x
x)V
(1
xV
x)V
(1
y)V
-
x(1
2xyV
s
a
a
s
s
s
w
s
w
s
a



+ +
= +
+
is
constant.

By definition the initial density (specific gravity)
is the initial mass of the must (water +sugar)
divided by the initial volume:
w
s
w
s
w
w
i
x)V
(1
xV
x)M
(1
xM
M
V
d + +
=
. Which can be
rewritten:
x
1
-
d
1
M
M
1
x
d
1
d
M
M
1
d
s
w
s
s
s
w
s
i




+ +
=

It is also possible to get x as a function of the
initial density:
1
d
d
d
d
1
M
M
1
-
x
1
i
i
s
s
w
s
=

Final density is by definition:
w
s
a
w
s
a
w
w
f
x)V
(1
y)V
-
x(1
2xyV
x)M
(1
y)M
-
x(1
2xyM
M
V
d +
+ +
+
=

This can be simplified using that the volume is
constant:
(
)
1
d
1
-
d
d
-
d
y
1
1
d
i
s
a
s
f



+

This expression can be modified to get the
attenuation as a function of d
i
and d
f
:
1
d
d
d
0,73
1
d
d
d
d
d
1
d
y
i
f
i
i
f
i
a
s
s

The alcohol by volume is equal to the volume of
alcohol (in ml) per 100 ml mead:
(
)
f
i
a
s
f
i
w
s
a
a
d
d
1,32
d
d
d
d
x)V
(1
y)V
-
x(1
2xyV
2xyV
ABV
+
+
=

So the attenuation and the alcohol by volume can
be calculated, knowning initial and final densities,.
The sugar by volume is:
a
s
f
i
s
i
s
i
w
a
s
s
d
d
d
d
1
d
1
d
1
d
1
d
y)
(1
x)V
(1
2xyV
y)V
-
x(1
y)V
-
x(1
SBV +
+
=

If all the sugar has been consumed (y = 1) :
(
)
(
)
1
d
0,37
1
1
d
1
d
d
1
1
d
i
i
s
a
f =

(
)
y
1
d
1,8
y
1
d
1
d
TV
i
s
i
a Mead made complicated: alcohol content
Mathieu
Bouville
2001-2002
2
If d = 1,
%
73
d
d
1
d
y
a
s
s
. So when the
density is 1, three quarters or so of the sugar
have been turned into alcohol (whatever the
initial density is). White labs publishes
attenuations for their yeasts of 70-80 %.
Examples (final density d
f
is equal to 0.995 in all
examples).







d
i
y
TVa
TVs
TMs
1,052
80,0 %
7,6 %
1,9 %
30 g/L
1,092
77,0 %
12,9 %
3,9 %
60 g/L
1,132
75,8 %
18,3 %
5,8 %
90 g/L
Table 9: some properties of mead as a function of original
gravity (final gravity is .995).
One can notice that there is a lot of sugar
remaining but the sugar content does not depend
on the final density only. So the final density should
not be used, as some people do, as a criterion to
determine whether the mead is dry or sweet.
Is there really so much sugar at the end? If so,
why do bacteria not attack all meads, not only the
sweeter ones?