[jlevensailor]

From what I've read (correct me if i'm wrong)

The point of a yeast starter is to give the yeast a weak gravity solution (1L water to 100G DME) to feast and grow on. For Saccharomyces, a lightly covered flask with a stir plate is best to both a) keep the yeast agitated and b) to oxygenate the yeast, which puts them in a reproductive aerobic phase.

My question: How long is too long to leave on a stir plate before pitching?

More specifically - If i have some lacto that i added to a starter on Monday and I'm waiting on a ph meter to come in the mail thats supposed to get here on wednesday next week, is that too long? Should I add some apple juice or dme so that it has something to eat?

[davidgzach]

Leave it on the stir plate until done and then put in the fridge, covered until you brew.  Let the yeast flocculate and fall to make a nice cake, decant and pitch.

Dave

Edit:  A few extra days in the fridge will not hurt anything....

[Jimmy K]

I don't know the answer, but I bet a lot of people will miss the fact that you're really asking about a lactobacillus starter. I wouldn't expect a lacto culture to perform the same way a yeast starter does.

[klickitat jim]

It will go until it stops then a long time after that it will begin to deteriate, but not in just a week or so. You're fine im sure

[JT]

I can't speak to lacto starters, I haven't done one.  I'm sure they're different.  S. Cerevisiae will burn through its reserves if it doesn't have food and you are constantly introducing oxygen using a stir plate.  It takes less than 24 hours for a 2 liter 1.040 starter on a stir plate to hit terminal gravity at 68 degrees from my testing.   

[jtoots]

I like this thread:
https://www.homebrewersassociation.org/forum/index.php?topic=20692.0

I'm pretty much a noob when it comes to starters...  One takeaway from this for me was that I now look for high krausen and put the starter in the fridge toward the end or just after it (please feel free to comment on that if you think I'm off track).

[brewinhard]

Lacto strains typically do not "love" oxygen which can actually inhibit their growth and reproduction for a bit.  When I make my lacto starters I usually use one wyeast pack in a 1.025 DME starter (1 qt) and let it sit with an airlock (no oxygen) for 5-7 days at around 95-98F.  I then carefully decant and pitch about 1.75 qts of 1.025 wort and yeast nutrient and let that ferment out for another 5-7 days before decanting and pitching.  I get decent sourness and acidity in a fairly short period of time with this method. 

So back to your OP - you will be just fine leaving the starter alone and not adding anything to it.  You might want to consider putting an airlock on it and even stepping it up one more time to increase your cell count.  Be advised that lacto takes more time to ferment out the wort than your typical yeast strains do.