Used to happen to me, but I found it wasn't an infection issue for me, but a yeast issue, particularly with some UK ale yeast such as WY1968. The theory was that the UK yeasts primarily bred for cask ales were meant to keep fermenting in the keg for natural carbonation, ie once the initial fermentation was over, they stalled but kept on working very slowly over an extended time. They, of course, did the same after bottling.
Would be nice if we knew what recipes you used, mash temps etc, how you oxygenated your wort, which yeast, OG and FG, fermentation time, priming sugar or dextrose and at what level. Hopefully that may get you a solution.
However, if it is an infection, I'm not your man to help you, as I've been lucky enough to never have had an infected batch.
Hmmm.. interesting. I do like the UK styles. But of the three i had problems with, two were common dry yeasts (Notto and S-04). The other was a recultured Coopers yeast. Here's the three i had problems with:
HOME BREW RECIPE:
Title: English Style Ale
Author: BrewMate
Brew Method: All Grain
Style Name: British Strong Ale
Boil Time: 60 min
Batch Size: 21 liters (fermentor volume)
Boil Size: 27 liters
STATS:
Original Gravity: 1.059
Final Gravity: 1.014
ABV (standard): 5.9%
IBU (tinseth): 41.35
SRM (morey): 37.8
Predicted Mash pH: 5.33
FERMENTABLES:
3.5 kg - Pale 2-Row (66.1%)
1.5 kg - Weyermann - Munich Type II Dark (25.9%%)
200g - Light Crystal Malt (3.5%)
320g - Flaked Barley (5.5%)
200 g - Aromatic Malt (3.5%)
75 g - Roasted Barley (1.3%)
HOPS:
30 g - Magnum, Type: Pellet, AA: 12.9, Use: Boil for 45 min, IBU: 41.35
MASH GUIDELINES:
1) Infusion, Temp: 67 C, Time: 45 min, Amount: 16 L
2) Sparge, Temp: 65 C, Time: 5 min, Amount: 16 L
OTHER INGREDIENTS:
0.25 tsp - Lactic acid, Time: 60 min, Type: Water Agt, Use: Mash
0.25tsp - Gypsum
YEAST:
Safale S-04 1 packet
Fermented 21C
OXYGEN
run off from keggle once cool into fermenter - splashed around then shook a few times once sealed.
FERMENTATION TIME:
In Primary for eleven days from runoff to bottling.
--
HOME BREW RECIPE:
Title: Russell's RIS (ended up more an Old Ale really)
Brew Method: All Grain
Style Name: Russian Imperial Stout
Boil Time: 60 min
Batch Size: 22 liters (fermentor volume)
Boil Size: 32 liters
STATS:
Original Gravity: 1.070
Final Gravity: 1.010
ABV (standard): 8.91%
IBU (tinseth): 81.01
SRM (morey): 33.31
Predicted Mash pH: 5.47
FERMENTABLES:
6 kg - Pale 2-Row (76.9%)
150 g - Roasted Barley (1.9%)
400 g - CaraAroma (5.1%)
250 g - Chocolate (3.2%)
200 g - Flaked Barley (2.6%)
300 g - Brown Sugar (3.8%)
NOTE - added 500 g - Dry Malt Extract - After two days primary ferment due to not hitting target gravity.
HOPS:
65 g - Magnum, Type: Pellet, AA: 10.2, Use: Boil for 60 min,
50 g - East Kent Goldings, Type: Pellet, AA: 6.2, Use: Boil for 5 min,
MASH GUIDELINES:
1) Infusion, Temp: 65.7 C, Time: 90 min, Amount: 18 L
2) Sparge - infusion- Amount: 15 L
OTHER INGREDIENTS:
0.75 tsp - Calcium Chloride (dihydrate), Time: 60 min, Type: Water Agt, Use: Mash
1.25 tsp - Gypsum, Time: 60 min, Type: Water Agt, Use: Mash
0.25 tsp - Baking Soda, Time: 60 min, Type: Water Agt, Use: Mash
YEAST:
Danstar - Nottingham Ale Yeast 2 packets
OXYGEN:
run off from keggle once cool into fermenter - splashed around then shook a few times once sealed.
OTHER:
Added one French Oak Spiral for three weeks once completed.
FERMENTATION TIME:
In Primary for four weeks total from run off to bottling
---
Here's another:
HOME BREW RECIPE:
Title: Foreign Stout
Author: BrewMate
Brew Method: All Grain
Style Name: Foreign Extra Stout
Boil Time: 60 min
Batch Size: 21 liters (fermentor volume)
Boil Size: 27 liters
Boil Gravity: 1.054
Efficiency: 74% (brew house)
Hop Utilization Multiplier: 1
STATS:
Original Gravity: 1.063
Final Gravity: 1.014
ABV (standard): 6.43%
IBU (tinseth): 41.35
SRM (morey): 37.8
Mash pH: 5.33
FERMENTABLES:
3.7 kg - Pale 2-Row (66.1%)
400 g - Rolled Oats (7.1%)
0.3 kg - CaraMunich III (5.4%)
600 g - Roasted Barley (10.7%)
400 g - Brown Sugar (7.1%)
200 g - Chocolate Malt (3.6%)
HOPS:
30 g - Magnum, Type: Pellet, AA: 12.9, Use: Boil for 45 min, IBU: 41.35
MASH GUIDELINES:
1) Infusion, Temp: 66.9 C, Time: 45 min, Amount: 16 L
2) Sparge, Temp: 65 C, Time: 5 min, Amount: 16 L
OTHER INGREDIENTS:
0.25 tsp - Lactic acid, Time: 60 min, Type: Water Agt, Use: Mash
YEAST:
Recultured Coopers Yeast active starter
Fermented 22C
OXYGEN
run off from keggle once cool into fermenter - splashed around then shook a few times once sealed.
OTHER:
Added one medium french oak spiral soaked in bourbon for three weeks
FERMENTATION TIME:
In Primary for four weeks total from run off to bottling