How do you detect infection in yeast starter?

Alright, so I'm a little paranoid with an infection in the last few batches... Anyhow, I'm working on a Two Hearted clone and got a bunch of yeast from bottles that has been going (bumped it up to about a liter last night). When I stepped it up last (and I'm a fairly careful brewer) I noticed it was fruitier than I expected, both in the aroma and flavor, and (if I'm not imagining things) there was just a hint of vinegar to the flavor. I was careful, hit around 1.040 with the gravity, added just a few hops pellets and some yeast nutrient. I know that starters aren't beer, so I'm wondering what the consensus is... should I pitch it? Should I throw it out and play it safe with Nottingham or Safale 05. What would you do? (And thanks in advance for your help.)

it will be smelling like butt and will have nasty white swirls..i think but not 100% never had an infected yeast starter

very hard to tell since we can't see or smell it ourselves so there will be no consensus. funky smells do not always mean infection and infections are relatively rare anyway.

only way to test before pitching would be to inoculate petri dishes with a solution of them (spread thinly over agar covered dishes I mean), let it grow under differetn conditions, and if they are more than one kind of cultures appearing, you have an infection. I am going through this myself, mostly out of pride to know that though I made some mistakes, I can fix the problem.

The way you coudl CLEAN your samples, is to increase the acidity of the petri dishes to I think 2.5 pH at most (coudn't find the number, still tracking it down these last few days) and then harvest the homogenous samples to use in building a fresh colony. The idea is that acidity of that maagnitude will kill all other cultures present.

BUT...... proper lab technique is the only way to prevent it tin the future,and it's only $7 for a pack, I woudl only need to pay 36 to get all the strains I care about back, but this is more about being a hobby than money saving, so it's all good right?

eastoak said:

very hard to tell since we can't see or smell it ourselves so there will be no consensus. funky smells do not always mean infection and infections are relatively rare anyway.

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This is kind of where I'm at... it's not outrageous and barely detectable... I'm guessing it's more the paranoia kicking in, but wanted to see what everyone thought on the matter. I'll check the larger starter and see what I think and make a call. Sounds like infection is pretty noticeable though... right?

mrbunn said:

This is kind of where I'm at... it's not outrageous and barely detectable... I'm guessing it's more the paranoia kicking in, but wanted to see what everyone thought on the matter. I'll check the larger starter and see what I think and make a call. Sounds like infection is pretty noticeable though... right?

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My Bell's harvest tasted pretty awful, but my starter got pretty warm. However, my ferment took off like a champ and when I racked to secondary yesterday the sample tasted amazing. I would start a little lower on OG when you first start to rouse them, but it sounds like you're ok to me.