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Re-reading this thread got me thinking about what is the major contributor to oxidation in the bottle (don't say "oxygen" 
) - oxygen that dissolves as you transfer, or oxygen in the headspace that dissolves during carbonation/conditioning/storage. Many homebrewers (especially new brewers) just syphon/rack directly into the top of the bottle, which splashes and can introduce oxygen, and other brewers use bottling wands. Obviously racking from a keg or with bottled CO2 is far better, but for many, this isn't an option. I figured I would just run some numbers and compare the two basic scenarios.
I just measured the amount of headspace in a fairly standard bottle by filling it with water to the 'normal' fill level, sticking it on some accurate scales, then topping up to the brim and seeing how much the extra water weighed.
Standard headspace (roughly) = 25g of water (=25 ml)
0.5cm headspace (as in the above thread) = 1g water (=1ml)
Under standard conditions, 1L of air contains 0.0094 moles of oxygen, which equates to 0.15g of oxygen.
This gives us:
'Standard' headspace = 3.75mg oxygen
0.5cm headspace = 0.15mg oxygen
So how does this compare to what is dissolved when you fill the bottle.
I think it's a relatively safe assumption to say that using a bottling wand transfers the beer to the bottle with negligible dissolved oxygen (let's assume for now that there is no oxygen ingress into your fermenter/botting bucket - obviously your setup could invalidate this assumption).
It's hard to tell how much oxygen dissolves in the beer when you rack directly into the bottle from a siphon tube/spigot. I don't have a DO meter, but we can try to re-use the results from oxygenating wort. Various measurements have been made over the ages when comparing oxygenation techniques, mostly trying to focus on maximising (rather than our goal here to minimize) the amount of DO in wort (which may or may not differ from the beer you are racking). Anyway, racking directly into the fermenter without splashing can get you as low as 0.7ppm DO in the wort, and splashing with agitation (rigorous shaking, which we don't do when bottling!) can give you as high as 4ppm. (lots of sources, but here is one and here is another). So for this, let's assume a conservative range of 1-4ppm. In reality, it'll probably be at the lower range as when racking we try to reduce splashing and dissolved CO2 will come out of solution and help reduce oxygen entering solution.
So how much oxygen is actually in a 500ml bottle at concentration rates of 1ppm? I'll assume water for calculating this quantity, as beer is 95% water. 500ml water = 500g. 1ppm of this is 500/1,000,000g = 0.5mg.
A 500ml bottle with 1ppm DO contains 0.5mg oxygen, and at 4ppm contains 2mg dissolved oxygen.
(It's been two decades since I did my Chemistry A-level, so please check my numbers!)
So what can we conclude from this?
Your conclusions may vary, but for me, if you bottle without CO2 and without using a bottling wand, the major contribution to oxygen in the bottle is actually from the headspace, not from oxygen that dissolves in the beer as part of the transfer as the beer splashes into the bottle.
There are many other factors that go into the oxygenation of the beer that aren't discussed here. How quickly does the dissolved oxygen stale the beer? How quickly does it get scavenged by the bottle conditioning (if you do that). How quickly/slowly does the oxygen in the headspace diffuse into the beer and what effect does this have? Once conditioning has finished, is there residual oxygen in the headspace that will slowly diffuse into the beer and not be able to be scavenged by the yeast and will oxidise the beer?
The standard practise for using a bottling wand (without CO2) is to bottom fill (we can assume negligible DO in this beer), but as you pull out the bottling wand air will come in to fill the headspace (if you don't flush with bottled CO2) - Assuming (without any reasoning or evidence) that racking without a wand splashes the beer and gets CO2 to come out of solution, could it be possible that this CO2 fills the headspace to prevent air coming in and using a bottling wand actually introduces more oxygen into the bottle than just racking with a siphon tube and letting it fall into the bottle?
I don't have any answers to the above, but this was an interesting academic exercise for me to see what contributes to oxygen in the bottle and gives numeric data behind why (obviously) the smaller amount of headspace in @Neale 's experiment had a great effect on the outcome of the beers after prolonged storage.
) - oxygen that dissolves as you transfer, or oxygen in the headspace that dissolves during carbonation/conditioning/storage. Many homebrewers (especially new brewers) just syphon/rack directly into the top of the bottle, which splashes and can introduce oxygen, and other brewers use bottling wands. Obviously racking from a keg or with bottled CO2 is far better, but for many, this isn't an option. I figured I would just run some numbers and compare the two basic scenarios.I just measured the amount of headspace in a fairly standard bottle by filling it with water to the 'normal' fill level, sticking it on some accurate scales, then topping up to the brim and seeing how much the extra water weighed.
Standard headspace (roughly) = 25g of water (=25 ml)
0.5cm headspace (as in the above thread) = 1g water (=1ml)
Under standard conditions, 1L of air contains 0.0094 moles of oxygen, which equates to 0.15g of oxygen.
This gives us:
'Standard' headspace = 3.75mg oxygen
0.5cm headspace = 0.15mg oxygen
So how does this compare to what is dissolved when you fill the bottle.
I think it's a relatively safe assumption to say that using a bottling wand transfers the beer to the bottle with negligible dissolved oxygen (let's assume for now that there is no oxygen ingress into your fermenter/botting bucket - obviously your setup could invalidate this assumption).
It's hard to tell how much oxygen dissolves in the beer when you rack directly into the bottle from a siphon tube/spigot. I don't have a DO meter, but we can try to re-use the results from oxygenating wort. Various measurements have been made over the ages when comparing oxygenation techniques, mostly trying to focus on maximising (rather than our goal here to minimize) the amount of DO in wort (which may or may not differ from the beer you are racking). Anyway, racking directly into the fermenter without splashing can get you as low as 0.7ppm DO in the wort, and splashing with agitation (rigorous shaking, which we don't do when bottling!) can give you as high as 4ppm. (lots of sources, but here is one and here is another). So for this, let's assume a conservative range of 1-4ppm. In reality, it'll probably be at the lower range as when racking we try to reduce splashing and dissolved CO2 will come out of solution and help reduce oxygen entering solution.
So how much oxygen is actually in a 500ml bottle at concentration rates of 1ppm? I'll assume water for calculating this quantity, as beer is 95% water. 500ml water = 500g. 1ppm of this is 500/1,000,000g = 0.5mg.
A 500ml bottle with 1ppm DO contains 0.5mg oxygen, and at 4ppm contains 2mg dissolved oxygen.
(It's been two decades since I did my Chemistry A-level, so please check my numbers!)
So what can we conclude from this?
Your conclusions may vary, but for me, if you bottle without CO2 and without using a bottling wand, the major contribution to oxygen in the bottle is actually from the headspace, not from oxygen that dissolves in the beer as part of the transfer as the beer splashes into the bottle.
There are many other factors that go into the oxygenation of the beer that aren't discussed here. How quickly does the dissolved oxygen stale the beer? How quickly does it get scavenged by the bottle conditioning (if you do that). How quickly/slowly does the oxygen in the headspace diffuse into the beer and what effect does this have? Once conditioning has finished, is there residual oxygen in the headspace that will slowly diffuse into the beer and not be able to be scavenged by the yeast and will oxidise the beer?
The standard practise for using a bottling wand (without CO2) is to bottom fill (we can assume negligible DO in this beer), but as you pull out the bottling wand air will come in to fill the headspace (if you don't flush with bottled CO2) - Assuming (without any reasoning or evidence) that racking without a wand splashes the beer and gets CO2 to come out of solution, could it be possible that this CO2 fills the headspace to prevent air coming in and using a bottling wand actually introduces more oxygen into the bottle than just racking with a siphon tube and letting it fall into the bottle?
I don't have any answers to the above, but this was an interesting academic exercise for me to see what contributes to oxygen in the bottle and gives numeric data behind why (obviously) the smaller amount of headspace in @Neale 's experiment had a great effect on the outcome of the beers after prolonged storage.
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I'll admit I'm assuming what others do and going on what I saw when I started. I know bottling wands are common, but not necessarily universally used.
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