New to kegging question

[Tony B]

I have not kegged before. I have a batch fermenting that is about 4.75 gallons including trub. I’m guessing I’ll end up racking about 4 gallons to the keg. It had an OG of 1.045 and should finish around 1.010. I was thinking I might boil some water and let it cool prior to kegging. Then add the water to the sanitized keg before purging and finally racking the beer to the keg, just to get a full 5 gallons. I know this would bring the FG down and I’m not too concerned about that. Looking for a light , smashable beer anyway. I was even thinking of adding a small amount of hops to the water as it’s cooling, kind of a hop stand. I’m thinking that would be safe as far as avoiding bugs and oxidation. Am I missing something?

 

[lumpher]

It will make it thinner and less mouthfeel, but if you're ok with that also, there's nothing wrong with your idea.

 

[Tony B]

It will make it thinner and less mouthfeel, but if you're ok with that also, there's nothing wrong with your idea.

Yeah, just a consideration. I may just stick with the 4ish gallons and get exactly what I brewed.

 

[IslandLizard]

Look up oxygen free transfer from your fermenter to your keg.
I've filled 5 gallon kegs with 2.5-3 gallons of beer, with no oxidation. The beer remained perfect from the first to the last pour.

It requires a 100% liquid pre-purged keg that remains closed (and full of CO2) after the full liquid purge. You'll fill it with beer through the liquid out post using a QD connected to your racking/siphon/transfer hose from your fermenter.

It's fairly simple, and beats the alternative. Once you do it you'll never go back.

Simulate ahead of time, with water and using a regular non-pre-purged keg, to get the method down and iron out any problems and kinks you may encounter.

 

[csantoni]

It requires a 100% liquid pre-purged keg

Just out of curiosity, why would this need to be done with 100% liquid?

I purge my kegs with just CO2 before filling them via a closed transfer and haven't had any problems I can detect. Is the 100% liquid purge something you need to do when doing a partial fill of a keg?

 

[day_trippr]

Knowing how you actually purge your kegs with CO2 will likely lead to the answer...

Cheers!

 

[csantoni]

Knowing how you actually purge your kegs with CO2 will likely lead to the answer...

Cheers!

Fill about half full with sanitizer, put on gas at about 8 psi and pump out all the sanitizer via a picnic tap. Then fill them up with just CO2 to about 8 psi, shut off the gas, pull the prv, repeat the gas purge about 3 or 4 times.

 

[mac_1103]

Fill about half full with sanitizer, put on gas at about 8 psi and pump out all the sanitizer via a picnic tap. Then fill them up with just CO2 to about 8 psi, shut off the gas, pull the prv, repeat the gas purge about 3 or 4 times.

Why only half full? Half full of sanitizer means half full of air, which means you're starting with a lot more oxygen than you would if you filled it all the way with liquid. Seems like your method will leave a fair bit of O2 in the keg.

 

[csantoni]

Why only half full? Half full of sanitizer means half full of air, which means you're starting with a lot more oxygen than you would if you filled it all the way with liquid. Seems like your method will leave a fair bit of O2 in the keg.

Mostly because one time I ran out of sanitizer and figured I'd see what happened if I didn't do a full liquid purge. I couldn't taste a difference in the beer so I started just using however much sanitizer I had on hand at the time which tends to be more like 2 or 3 gallons instead of 5. Definitely one of those things that probably isn't the "right" way to do it but seems to work for me.

 

[day_trippr]

And there it is.

fwiw, if timing works I purge pairs of kegs from the pairs of fermentors I use for each 10 gallon batch. But if I don't have empty kegs available I'll do the "Star San Purge", totally filling the keg with standard Star San/water mix, then push it all out with CO2...

Cheers!

 

[csantoni]

So I guess the answer to my original question is the 100% liquid purge is required because that's the correct way to do it.

 

[mac_1103]

So I guess the answer to my original question is the 100% liquid purge is required because that's the correct way to do it.

Well yeah, if you actually want to purge the keg of oxygen.

 

[IslandLizard]

So I guess the answer to my original question is the 100% liquid purge is required because that's the correct way to do it.

If you use fermentation CO2 to purge your kegs, in most cases a liquid purge is not absolutely needed.

 

[day_trippr]

So I guess the answer to my original question is the 100% liquid purge is required because that's the correct way to do it.

It's all a matter of how comprehensive one wants to be - and to a large extent how vulnerable to oxidation the beer styles one keeps on tap.

Fortunately that's entirely up to the individual, but I always recommend "the full monte", mostly because 3 out of the 6 beers I keep on tap have been New England IPAs for the last many years and they really do not like oxygen, full stop. Taking the hard core approach, however, I can keep them bright and delicious for as long as six months.

Pour a beer and peruse the efforts of our resident gas physics guru...

https://www.homebrewtalk.com/threads/keg-purging-with-active-fermentation.628658/#post-8004741

Or jump to these two images:

and

which show actually bringing the O2 content down to low PPB numbers isn't all that easy...

Cheers!

 

[csantoni]

how vulnerable to oxidation the beer styles one keeps on tap.

Very good point. My 5 gal batches which don't get a full liquid purge are almost always light lagers. When I make anything dark or hoppy I do 3 gal into a 3 gal keg and they get the full liquid purge (or pretty darn close). Maybe I've just been getting lucky with the big batches, they get drunk about as fast as I can make them.

 

[jtgoral]

What is a difference in 4 gallons filled keg and keg filled with 5 gallons and 1 gallon removed through the tap couple weeks later? In both cases there is CO2 above the beer.

 

[IslandLizard]

What is a difference in 4 gallons filled keg and keg filled with 5 gallons and 1 gallon removed through the tap couple weeks later? In both cases there is CO2 above the beer.

In a 100% prepurged keg (100% meaning there's 0 or very close to 0 ppm oxygen content in that keg) it won't make a difference. That is, as long as the prepurged keg is filled without opening (the lid), so no air (21% oxygen) can go in there.
The method of transferring the beer from the fermenter can make a difference too, a closed transfer being the best way.

When you don't prepurge the keg, just fill it with beer, you're left with air in the headspace. About 1.25 gallons in the headspace when filling with 4 gallons, or 0.25 gallons (about a quart) when filled with 5 gallons of beer. The smaller headspace left in the 2nd example is easier to purge (fewer purges necessary) than the 1st example to bring the residual O2 to a low enough level. See the table, above, in #14.
This does not include the amount of O2 being absorbed by the beer during the process of filling, which is relatively highly turbulent.

Of course, dispensing a gallon of beer (using bottled, pressurized CO2) from the more completely filled keg won't introduce more oxygen to the keg and beer that's left in it. That is as long as the gas (and in lesser degree liquid) tubing used is gas impermeable, such as EVA Barrier tubing.

 

[Tony B]

I’m hopefully buying 3 used ball lock kegs from someone on OfferUp this week. I plan to completely disassemble and wash the shite out of them with PBW. I’m replacing all O-rings and dip tubs with the floating variety. Before racking to them, I am planning to fill one completely with Starsan solution and push it through the first 2 with CO2 and leave in the third. I will have 2 batches ready to keg shortly thereafter.
If you start with near 100% full volume of liquid Starsan and transfer with co2, there can only be but a negligible amount of O2 in the tank.