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Old 05-06-2013, 10:16 AM   #1
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Default When is overpitching actually overpitching?

I have recently started using liquid yeast. I brew small batches (5 litres) so do not need to use a starter but do so that I can harvest yeast for future brews. I normally make a 1 litre starter and save half and pitch half. However, I suspect that this might be too much yeast for my small batches so wanted to run some numbers past the HBT crowd for some feedback.

Using Yeastcalc for my latest starter it says that I will end up with 161 bn cells from a 1 litre starter (regular shake method) and that for my planned brew I only need 48 bn cells. Keeping in mind that I only pitch half the starter (80 bn cells) that means I will be overpitching by 32bn cells. So my question is; is this rate of pitching likely to be a problem or am I still within an acceptable range of overpitching (if such a thing exists)?

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Old 05-06-2013, 06:41 PM   #2
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I would love to know this too.

When pitching yeast from rinsed yeast, I'm making a couple of assumptions (number of cells/ml of slurry and viability). When pitching from a Wyeast packet, you are assuming you really start with 100 billion cells and you are assuming the viability based on date. And when you make a starter, you are assuming the growth rate. So while I'm careful to calculate the number needed and make a starter for that much, I'm making so many assumptions that I have a feeling I could easily be off by +/- 30% (or more ). But is it really a big deal? Which way is worse - under or overpitching?

Sorry I didn't really answer your question but hopefully someone will.

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Old 05-06-2013, 08:20 PM   #3
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Is always better to have at least a starting point using pitching calculator. with exirience you will be able to see different kind of yeast bheaviuor depending on the viability of the yeast; but for sure this kind of consideration ca be taken replicating the same beer with the same yeast several time.

For example: my yeast calculator tell me that that pack of yeast used for a 2liters started should give me 200bil of yeast cell. Than I make the starter (stir plate at 22°C)and see that it has a lag time of 4 hours (colour changed from brown to cappucino like), at the end the sediment is 1 inc thick; the lag time of fermentation is 15hours and ti reach the final attenuation in 8 days. Than the next time I have a pack of yeast wich is 2 month older, so the calculator tell me that i should end up with 150bil yeast cell. I make the same starter and the same beer and i report the results. You will notice that the lag time of the starter is much higher (one day for example) and the sediment is 1 inc thick but it has 2 distinctive layers with different color (the bottom one is darker). I don't know if that number (150bil) is true, but I sure know that the next time if I have another yeast pack with that age I should consider make two starters.
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Old 05-06-2013, 08:36 PM   #4
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Well, there's only one accurate answer you're going to get, but I don't think it's going to help you. You're overpitching when, due to the high levels of yeast pitched, you're getting worse beer than if you had pitched less.

Since "worse" here is dependent upon your expectations and later evaluation of the finished product, only you can answer that question. It's also going to depend a lot upon what yeast you use, what the recipe is, how much you aerate, and so forth for many factors. See? Not very helpful, but very accurate.

As for practical advice, here are a few thoughts. You're not pitching that much above "standard rates," so I don't think there's any immediate cause for concern. Do you detect anything off about your beers? If not, carry on. Your increased rates will definitely be changing the beer, but maybe that change isn't bad, or maybe it's just not significant to the flavor/experience of the finished product. If you do detect flaws, or you just want to test that variable to see if you can improve things a bit, try pitching 1/3 of the starter instead of 1/2 next time, or measure a bit more accurately and do a split batch. Experiment and see what happens. If that all sounds like too much trouble, then like I said earlier, in so many words, if it ain't broke...
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