HLP, Lactobacillus, and the number of colonies needed to sour a beer

[kmcd]

Would someone please point me towards a good resource (or offer first hand advice) regarding the number of colonies of lactobacillus in an HLP test and how shelf stable that beer is? I know zero colonies is ideal—and thankfully most of my HLP tubes grow zero colonies—but I have some tubes growing lactobacillus from samples of recently packaged beer. The cans of beer taste great right now, but I don’t have a clear understanding of how long it will take the lactobacillus to make itself felt on anyone’s pallet.

I inoculated my HLP tubes with 1ml of beer. One tube has grown 7 colonies in 2 days. Another tube has 9 colonies. They’re the distinct ghost/tornado/teardrop shape of lacto.

We have a temporary hold on this beer while I perform additional testing and handwringing. I’m looking for any advice on potential shelf stability, resources for additional testing I might do, and any firsthand accounts for dealing with this type of issue. Thanks ya’ll!

[AT-JeffT]

The Quality Management book by Mary Pellettieri has a sample QA plan with a limit of 5 cfu per 1mL.

Setting hard numbers on things like this is very difficult, it's quite situation dependent. It also depends on your organizations tolerance for risk.

Whatever you do, use this batch to learn how much of a shelf life 7 cfu/mL of lacto gives you. I would take pH and HLP samples from the cans every week or so. I might also incubate some at warmer temps and some at room temp.

[R.Cockerell]

Sorry to hear about the bugs. We encounter positive HLP results infrequently enough that for now we treat any colonies in HLP as too many but like Jeff was suggesting there's just no real way to know without more testing. No one wants to go on record saying that a certain number is safe and another isn't mainly because, without replicates, plating techniques for microbes can't be treated as absolutely representative of what's happening in the sample. Depending on how a sample is treated it's feasible that you would kill some of the microbes before they had a chance to multiply and conversely you may have sampled a more heavily contaminated sample, homogeneity not being guaranteed in large volumes and all. Another complicating factor is that not all anaerobic or microaerophillic organisms are going to behave differently in a beer so without knowing species ID it's complicated to predict what will happen. Start by pulling a colony from the tube and gram stain it, record it's gram reaction so that you can start to get an idea of what it may be. Lastly, every brewery has different times that their beers are in the market (not always refrigerated) based on sell by dates arranged with the distributors and retailers or just how quick it sells which is yet another reason why a set number of cfu's isn't readily available.

[kmcd]

Thanks for the replies! I understand there's no hard numbers in this, but I appreciate the advice nonetheless.

I was speaking with a lab tech at a much larger brewery who told me they've had canned batched come back positive for lactobacillus in the past, but after two weeks cold storage those cans are often clear of any infection. His explanation was that the cold temperatures can kill off lactobacillus before a significant amount of lactic acid is created. Does this sound right to anyone? I've never read or heard or experienced anything exactly like what he told me.

[AT-JeffT]

Thanks for the replies! I understand there's no hard numbers in this, but I appreciate the advice nonetheless.

I was speaking with a lab tech at a much larger brewery who told me they've had canned batched come back positive for lactobacillus in the past, but after two weeks cold storage those cans are often clear of any infection. His explanation was that the cold temperatures can kill off lactobacillus before a significant amount of lactic acid is created. Does this sound right to anyone? I've never read or heard or experienced anything exactly like what he told me.

This does not sound right to me. I've stored Lacto cultures in the fridge for much longer than two weeks and was able to get viable cells to grow on plates repeatedly. Lactobacillus spoils milk, it definitely doesn't get killed at refrigerator temperatures.

[dberg]

Thanks for the replies! I understand there's no hard numbers in this, but I appreciate the advice nonetheless.

I was speaking with a lab tech at a much larger brewery who told me they've had canned batched come back positive for lactobacillus in the past, but after two weeks cold storage those cans are often clear of any infection. His explanation was that the cold temperatures can kill off lactobacillus before a significant amount of lactic acid is created. Does this sound right to anyone? I've never read or heard or experienced anything exactly like what he told me.

Every lager brewery would love for this to be true; unfortunately, it's not.