Longevity advice (and other bits)

[MattPark]

Hi Guys
So I just finished my first ever brew (Coopers English Bitter) which I was quite impressed with despite my crude knowledge and skill.
I have trawled through a number of threads on techniques and devices which can be used but my questions are these:
I pulled my brew from a regular pressure barrel direct to an Angram hand pump.

Now I didn't expect the brew to last too long as I was having my Dad, brother and a couple of mates round so alls I did was to open up the inlet valve on the lid slight to allow air to enter so I could draw from the pump (I know that air spoils the brew but as it wasn't going to be around long..hey!) Then at the end of the night, I blasted some CO2 into the barrel then sealed the lid once more. the next day came to it, opened up the inlet to release the pressure and carried on drinking and again repeated the CO2 process again.
The following day (Day 3) I could taste the difference but there was only a few pints left in the barrel.

a) Would the taste difference be because of spoiling or because they were the las pints in the barrel?
b) I now have a Check valve in line in between the barrel and pump, would this alone be enough to make the beer last around a week, I would never expect 40 pints to last much longer than that in my house!?
c) Would a Cask breather (which I have read about) really make that much of a difference, I didn't really want to connect my bitter to CO2?

Thanks in advanced Guys.

 

[RobWalker]

You know when you leave a pint out for half an hour and it gets a sort of cringey quality to it? That's oxidization, the same thing that turns wine and cider to vinegar, and that's what happened to your beer. In beer you get a wet cardboard taste.

Not sure about using a pump, never done it, but my usual process is to blast it with co2 immediately on kegging, then open the lid a few times and reseal before it runs out to get the oxygen out. From that point on, it's gotta be under pressure all of the time, with no exposure to air whatsoever.

 

[MattPark]

I use a hand pump for my house beer, usually a 3.5 to 4% pale ale.
You do not add co2 under pressure, normal the barrel sucks in air as the beer is drawn.
To keep beer fresher longer I made a baloon with a co2 valve which I plumber into the barrel. The baloon fills with co2 from the priming and I top up with a small bottle.
So when I pull a pint it draws in co2 not air
.

I just remembered this guy from a different post which looks quite effective - so as the brew is priming, it releases CO2 into the balloon (sealed bag) so when it comes to drawing the beer off with a hand pump it sucks in CO2 and not air.
What do you reckon?
And if the guy who posted that sees this - how and with what did you make the CO2 balloon?
Thanks