Make your own cheap CO2 generator
In regards to my initial batch (recipe 1) I was a little worried about transferring the mead from one
fermenter to another and loosing the protective CO2 layer covering the surface. CO2 is heavier than
air so all I need is just enough to cover the surface. That said, I am not sure that there is enough in
the solution to generate a new layer.
What to do then? Buying a CO2 spray is expensive and using compressed gas you need expensive
equipment. So why not just prepare a CO2 generator yourself.
All you need is sodium bicarbonate (= baking powder) and citric acid. Both chemicals are available
in any drugstore (for example Matas here in Denmark)
Generation of 5 L of CO2
Equipment:
- A flask that can contain 250 ml
- A stopper for the flask with a tube that can be used as a transfer line to the fermenter
- A decent scale
- A beaker that can contain a bit more than 100 ml
Procedure:
1) Add 20 g of sodium bicarbonate to the 250 ml flask
2) Add 30 g of citric acid to the beaker and dissolve in 100 ml of water. It dissolves slowly but
surely with a gentle agitation
3) Add the citric acid solution in small steps to the 250 ml flask (I usually add in 5 steps with
the smallest volume added first)
4) After each addition close the flask with the stopper and attach the other end of the tube to the
airlock of the fermenter. Ensure that the lid is partially opened so that excess air can escape.
(I just inserted a spoon in a small opening)
5) When all the sodium bicarbonate has dissolved fully and the solution is no longer fizzing the
reaction is over.
6) Remove the CO2 generator, close the lid firmly and attach the airlock.
Very simple :o). With whatever losses of CO2 in this set-up you should at least get 2 L into the
fermenter which is plenty to cover the surface. The reaction endothermic so you can feel a slight
cooling effect in the reaction flask. Also pH of the solution after reaction is about 5 so it can poured
in the sink when cleaning up.
___________
If you find it interesting to see why I ended up the 20 g citric acid and 30 g sodium bicarbonate then
read on :o).
Using the ideal gas equation I can find that at 22oC I need 0.23 mol CO2 to generate 5.5 L of gas
= ~5 L for use and ~0.5 L to fill the flask and tube.
Sodium bicarbonate and acid generates CO2 and water as shown below
NaHCO3 + H+ --> CO2 + H2O + Na+
... so 1 mol of sodium bicarbonate becomes 1 mol of CO2.
So 0.23 mol of NaHCO3 equals 19 g since the molecular weight is 84 g/mol. Assuming a purity of
95% then 20 g is needed.
Citric acid is used because it is easily available and non-volatile and non-toxic. Citric acid actually
contains 3 acid groups, so 1 mol of citric acid is equivalent with 3 mol H+. But when the reaction
has ended pH of the solution is about 5 which is in the range of pKa(2) of 4.75, hence 1 mol of citric
acid only releases about 1.5 mol H+.
If 1 mol citric acid releases about 1.5 mol of H+ then only 0.15 mol of citric acid is required. The
molecular weight of anhydrous citric acid is 192,1 g/mol which means that 29 g of citric acid is
needed. Again, assuming a purity of 95%. the actual amount becomes 30 g.
fermenter to another and loosing the protective CO2 layer covering the surface. CO2 is heavier than
air so all I need is just enough to cover the surface. That said, I am not sure that there is enough in
the solution to generate a new layer.
What to do then? Buying a CO2 spray is expensive and using compressed gas you need expensive
equipment. So why not just prepare a CO2 generator yourself.
All you need is sodium bicarbonate (= baking powder) and citric acid. Both chemicals are available
in any drugstore (for example Matas here in Denmark)
Generation of 5 L of CO2
Equipment:
- A flask that can contain 250 ml
- A stopper for the flask with a tube that can be used as a transfer line to the fermenter
- A decent scale
- A beaker that can contain a bit more than 100 ml
Procedure:
1) Add 20 g of sodium bicarbonate to the 250 ml flask
2) Add 30 g of citric acid to the beaker and dissolve in 100 ml of water. It dissolves slowly but
surely with a gentle agitation
3) Add the citric acid solution in small steps to the 250 ml flask (I usually add in 5 steps with
the smallest volume added first)
4) After each addition close the flask with the stopper and attach the other end of the tube to the
airlock of the fermenter. Ensure that the lid is partially opened so that excess air can escape.
(I just inserted a spoon in a small opening)
5) When all the sodium bicarbonate has dissolved fully and the solution is no longer fizzing the
reaction is over.
6) Remove the CO2 generator, close the lid firmly and attach the airlock.
Very simple :o). With whatever losses of CO2 in this set-up you should at least get 2 L into the
fermenter which is plenty to cover the surface. The reaction endothermic so you can feel a slight
cooling effect in the reaction flask. Also pH of the solution after reaction is about 5 so it can poured
in the sink when cleaning up.
___________
If you find it interesting to see why I ended up the 20 g citric acid and 30 g sodium bicarbonate then
read on :o).
Using the ideal gas equation I can find that at 22oC I need 0.23 mol CO2 to generate 5.5 L of gas
= ~5 L for use and ~0.5 L to fill the flask and tube.
Sodium bicarbonate and acid generates CO2 and water as shown below
NaHCO3 + H+ --> CO2 + H2O + Na+
... so 1 mol of sodium bicarbonate becomes 1 mol of CO2.
So 0.23 mol of NaHCO3 equals 19 g since the molecular weight is 84 g/mol. Assuming a purity of
95% then 20 g is needed.
Citric acid is used because it is easily available and non-volatile and non-toxic. Citric acid actually
contains 3 acid groups, so 1 mol of citric acid is equivalent with 3 mol H+. But when the reaction
has ended pH of the solution is about 5 which is in the range of pKa(2) of 4.75, hence 1 mol of citric
acid only releases about 1.5 mol H+.
If 1 mol citric acid releases about 1.5 mol of H+ then only 0.15 mol of citric acid is required. The
molecular weight of anhydrous citric acid is 192,1 g/mol which means that 29 g of citric acid is
needed. Again, assuming a purity of 95%. the actual amount becomes 30 g.
= ~5 L for use and ~0.5 L to fill the flask and tube.
Sodium bicarbonate and acid generates CO2 and water as shown below
NaHCO3 + H+ --> CO2 + H2O + Na+
... so 1 mol of sodium bicarbonate becomes 1 mol of CO2.
So 0.23 mol of NaHCO3 equals 19 g since the molecular weight is 84 g/mol. Assuming a purity of
95% then 20 g is needed.
Citric acid is used because it is easily available and non-volatile and non-toxic. Citric acid actually
contains 3 acid groups, so 1 mol of citric acid is equivalent with 3 mol H+. But when the reaction
has ended pH of the solution is about 5 which is in the range of pKa(2) of 4.75, hence 1 mol of citric
acid only releases about 1.5 mol H+.
If 1 mol citric acid releases about 1.5 mol of H+ then only 0.15 mol of citric acid is required. The
molecular weight of anhydrous citric acid is 192,1 g/mol which means that 29 g of citric acid is
needed. Again, assuming a purity of 95%. the actual amount becomes 30 g.
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