Hi. I have a question about G03. It’s not flocculating and is super hazy. Do you know what might be causing this?
That’s strange, G03 should flocculate pretty well. Is this a fresh pitch, or a pitch that has been harvested? What’s the batch size and original gravity?
It’s harvested. The batch size is 5 barrels. The original gravity is 12.5P. We usually start with 3 pouches into 2.5 gallons of wort, before topping off with 5 barrels of wort.
Okay. So you’re propagating yeast from pouches for 5 barrels of wort, and then harvesting from there? Can you tell me about your propagation process? How long do you run the propagation and do you aerate? Also, are you performing cell counts and viability assessments when you harvest and re-pitch?
Yes, we’re propagating with wort from another batch 11P. We add oxygen during knockout. After 24 hours, we add the 5 barrel batch of 12.5P wort, which we harvest and repitch when it’s finished. We don’t have a microscope and are not counting cells. I know it’s not perfect, but it’s how we’ve always done it.
I’m wondering about the amount of growth you’re getting from three pouches and the resulting pitch rate once the final 5 barrels are added. We generally recommend a pitch rate of around 0.75 million cells/mL/ºP. To achieve this in 5 barrels of 12.5ºP wort, we’d need to reach 7.7 trillion total cells during the propagation, before the final volume is added.
Under ideal propagation conditions, we’d hope to see each cell double 3.0-3.5 times in around 48+ hours. In your case, three pouches are supplying 600 billion viable cells. If they were to double 3.0-3.5 times, the terminal cell count would be around 7.2 trillion cells, which would be close to the target (7.7 trillion cells). Based on what you’re describing however, I don’t think we’re achieving this growth.
The propagation wort volume, the amount of dissolved oxygen, the temperature and the amount of time before the final volume is added may all be affecting cell growth. It’s difficult to say exactly what the cell count is without quantification, but in 24 hours you’re probably only achieving 1.0-1.25 doublings. If so, then this would be closer to ~1.2 trillion cells by the time the final volume is added. This is a pitch rate closer to 0.12 million cells/mL/ºP, a pretty significant underpitch.
When yeast is underpitched, they can experience a lot of stress, affecting healthy new cell growth and flocculation characteristics. I’d recommend adjusting the propagation pitch size to ~10% of the final volume. This is 0.5L of yeast in 0.5 barrels of well oxygenated wort. The initial cell count and propagation volume is a bit higher and allows for more growth. I’d also add a yeast nutrient with zinc and magnesium, if you’re not already, and run the propagation for at least 48 hours before knocking out the final volume. These steps should help you achieve a higher cell count and improve flocculation characteristics.
Thank you so much! I figured we were off, but I wasn’t sure. We’ve used pouches for a long time. Is it possible to order G03 in 0.5L sizes? What is the cost?
No worries! Yes. 0.5L is our minimum pour size for in-stock strains. Customerservice@imperialyeast.com would be happy to help get pricing information and an order going for you when you’re ready. Cheers!