A38 Multi-knockout: Equipment failure: High gravity wort

I have a quick question about a beer we have going using <a title="A38 Juice" href="https://www.imperialyeast.com/yeast-strains/juice" target="_blank" rel="noopener">A38 Juice</a>.
We were planning on running a split brew, 20 barrels yesterday and 20 barrels today. Our boiler went out just after knocking out the first 20 barrels yesterday.
We should have the boiler back up and running later today. Do you think it would be fine to brew the final 20 barrels tomorrow, knocking out roughly 36 hours after the last knockout? 
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Just for clarification. The first 20 barrels were brewed yesterday? Was this a single batch or two batches? How much yeast did you pitch yesterday? 
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Yes, we brewed two 10 barrels turns for a total of 20 barrels at 18.5&ordm;P. The last batch went in around 6pm. The temperature was 67&ordm;F. The pitch rate was 1.0 million cells/mL/&ordm;P for the first 20 barrels only.
We wanted to add the final 20 barrels today, but we&rsquo;re not able to. Do you think we should hold off and just brew the final 20 barrels after this batch is completed, or move forward with the last 20 barrels tomorrow? Also, we were wanting to add roughly 2-3&ordm;P worth of sugar at high krausen.
What are your thoughts on this?
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Got it. Thanks! The 36 hour window might actually be a good thing. With this high of an original gravity, you&rsquo;re going to want the additional cell growth that occurs during this time.
Knocking out the final 20 barrels tomorrow, with oxygen as normal, should be just fine. A38 requires 25 ppm of oxygen. With the final 20 barrels, the DO will drop to ~12.5ppm and be taken up immediately. I really wouldn&rsquo;t worry about oxidation here.
Regarding the extra sugar. It would be best to dissolve this on the hotside in the final two batches before knockout. 
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Thanks a lot for this information. We brew split batches quite often and usually see a drop in gravity within the first 24 hours. I&rsquo;m sure this is similar, knocking out while the yeast is in an anaerobic state. I just wasn&rsquo;t sure about the additional gap in time and associated risks.
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It&rsquo;s really good to keep this in mind, but in this case with such a high gravity, hitting peak cell growth before adding fresh wort is really going to help. I wouldn&rsquo;t be too concerned. Cheers! 
</blockquote>

Yeast Management: Cold vs Warm Pitch

My question is about pulling yeast out of cold storage before pitching. Should we be pulling our yeast brink out to warm up to near fermentation temperatures before pitching? Or, is it alright to pitch directly after pulling the brink out of the walk-in? What are the stressors/ effects on the yeast/ fermentation if we're not letting the yeast warm up?
<blockquote>
Great questions! It's actually better to pitch the yeast cold, rather than let it warm up first. As yeast warms up, they become active. This should happen in an environment where there&rsquo;s plenty of oxygen, nutrients and sources of energy available. If they become active in the yeast brink without these resources available, they&rsquo;ll begin depleting their own stores of glycogen. This and the build of CO2, can be extremely harmful to yeast and has the potential to decrease the viability. The effect here would be slow or stalled fermentations, longer VDK reduction times, and/or issues with flavor and aroma.
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We thought the temperature swing would be a stressor, but this makes a lot of sense. Thank you for your help!

A38: Slow/Stalled Fermentations: Multi-knockout: Propagation: Oxygen: Blow-off Overflow

I&rsquo;m wondering if you can help me with your A38 Juice yeast. It&rsquo;s been taking longer to hit terminal gravity and some of our batches have been stalling. There have been no process changes, we&rsquo;re doing everything the same. We&rsquo;re brewing 20 barrel batches at 17.5&ordm;P. Any thoughts on what might be going on?
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Are these with fresh pitches of yeast, or with harvested yeast?
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This happens with our harvested yeast and gets worse over time.
<blockquote>
What is the target pitch rate, and how are you quantifying this? Are you adding oxygen during knockout? If so, what is the target ppm of dissolved oxygen (DO)?
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We&rsquo;re harvesting about 30 pounds for 20 barrels. We don&rsquo;t do cell counts. I&rsquo;m not sure what my pitch rate is. This is how our old head brewer set it up. We add oxygen during the first knockout. I&rsquo;m not sure what the DO is. We go by sight through the sight glass.
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Is this a single 20 barrel batch, or multiple knockouts?
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Multiple knockouts. We do one 10 barrel turn and then another 10 barrel turn the next day.
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Okay, thanks. When we see issues like this it&rsquo;s usually due to low viable cell counts. When re-pitched, the issues compound from generation to generation. We need to pin-point where this may be coming from. In multi-knockout situations, we typically recommend pitching enough yeast for the volume of wort brewed on the first day. I&rsquo;m wondering if 30 pounds is achieving a pitch rate that&rsquo;s in the ballpark for the first 10 barrels? It&rsquo;s difficult to say for sure without quantifying this under a microscope, but we can estimate it.
We typically recommend a pitch rate of 0.75 million cells/mL/&ordm;P. To achieve this pitch rate for 10 barrels of 17.5&ordm;P wort, our online &nbsp;<a href="https://www.imperialyeast.com/resources/brewing-calculators#3">Pitch Rate Calculator</a> indicates 12L of yeast. This calculation uses Imperial Yeast&rsquo;s viable cell count. Since you&rsquo;re using harvested yeast, your viable cell count may be lower. To be safe, let&rsquo;s err on the low side and assume ~10%.
To double check your pitch size, we know that 1L of yeast slurry is 2.2 pounds. So, a 12L pitch would be 26.4 pounds. If we add 10% slurry to make up the possible difference in viability, then this comes out to 29 pounds of harvested yeast slurry. For 10 barrels, 30 pounds is probably in the ballpark.&nbsp;
Since the pitch size is close, we should think about oxygen. A38 performs best with 20-25 ppm of dissolved oxygen. It&rsquo;s difficult to say what the DO levels are without measuring it, but adding O2 to the first batch alone probably isn&rsquo;t enough to achieve proper cell growth once the second batch is added. I&rsquo;d recommend adding oxygen to both batches. I&rsquo;d also recommend using this <a href="https://www.medicalgasinstallers.com/product/0-8-lpm-oxygen-flowmeter/">O2 Flowmeter</a> and <a href="https://www.imperialyeast.com/resources/brewing-calculators#3">DO Calculator</a> to help dial in the specific amount of oxygen necessary to achieve the recommended DO level. This is just an estimation, but it should help get you close.
I have one more question. Do you see excessive overflow during blow-off?
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Yes, we see quite a bit of material coming out of the blow-off.
<blockquote>
This might be part of the issue as well. A38 is a chain forming strain and is capable of climbing out of the FV,&nbsp; literally losing yeast cells to the floor. Rather than issues with viability or growth, there may just not be enough cells left in the FV to attenuate the batch fully or to harvest at TG. I&rsquo;d recommend adding a bit of antifoam to the fermenter when pitching the yeast. This shouldn&rsquo;t impact head retention, flavor, or aroma, but it should help keep yeast cells in the fermenter.
Together, making some adjustments to oxygen during KO and adding antifoam during fermentation, should help increase (and maintain) the overall cell count, improving the fermentation times and stalling issues.
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Thank you so much for this information! We&rsquo;ll look into the O2 flowmeter and antifoam. We&rsquo;ll keep you posted.

L28 Increased Attenuation

In the past month, we&rsquo;ve noticed that the gravities have been finishing lower than usual when using L28. It usually finishes at 2.5&ordm;P, but has been finishing at 2.0&ordm;P. I&rsquo;ve tried troubleshooting this, but our process looks pretty consistent. There are no major changes to top-off volumes, mash temperatures, or original gravities etc.
What could be affecting the final gravity? We do pitch cone to cone, but even if a slightly larger volume of yeast were added shouldn&rsquo;t the final gravities be the same, because it&rsquo;s not like there are more sugars in the wort?
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You are correct. Adding more yeast will not result in higher levels of attenuation, unless what was added before was severely under-pitched or stressed out. I don't think this is the issue here. You'd see a lot of other accompanying signs if this were the case. 
You're also correct that FG is typically determined by the amount (and type) of sugars available to the yeast. It might be worth looking into factors affecting wort composition a bit more. Some areas that come to mind are, differences in malt COA&rsquo;s (protein levels and diastatic power specifically), variations in mash temperature, pH and liquor to grist ratio, mashout temperature and the amount of time it takes the grain bed to reach denaturing temperatures.
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For lagers, we typically mash at 152&ordm;F and rest for 60 minutes. We mash out at 168&ordm;F, but I&rsquo;m not sure how long it takes to get there. Would a +/- 5&ordm;F difference in mash temperature make that big of a difference in final gravity?
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The short answer is yes, +/- 5&ordm;F can make a big difference in final gravity. A 60 minute mash rest held at 152&ordm;F is going to be pretty fermentable. You could try increasing the mash temperature slightly, 154&ordm;F may be a good compromise. Another option may be to increase the liquor to grist ratio (L:G) slightly, if it&rsquo;s pretty thick. If adjusting the mash temperature and/or L:G doesn&rsquo;t help, then you might try adjusting the time it takes to reach 168-170&ordm;F during sparge by shortening the mash rest time. 
Malts are so highly modified and carry such high loads of diastatic power (DP) that enzymes can remain active until fully denatured throughout the grain bed or in the kettle. The goal here is to reach denaturing temperatures as soon as possible. Performing an Iodine test during the mash rest will help determine when the starch has been converted, and when it&rsquo;s time to move on to Vorlauf (recirculation). If it only takes 30 minutes, then beginning collection and sparge 30 minutes sooner may help decrease further enzymatic breakdown to fermentables by 30 minutes. 
Another thing to note is that bagged malts can be pretty inconsistent and may vary depending on lot number and seasonality. If you&rsquo;re using bagged malt, then it may be helpful to keep track of the lot numbers and the COA&rsquo;s, if possible. At the very least, when you receive a lot that has higher levels of DP, or has been shown in your brewhouse to produce variations in wort fermentability, you might be able to compensate ahead of time with some of these hot side adjustments. 
From a yeast perspective. It&rsquo;s best to aim for a consistent pitch rate with healthy viable yeast, supply an adequate and consistent level of dissolved oxygen during knockout, and maintain consistent temperatures within the strain&rsquo;s fermentation range. If these are dialed, then there shouldn&rsquo;t be an issue with attenuation.
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Our mash tun is not jacketed so we only &ldquo;control&rdquo; the temperature by the water we put in. After 60 minutes in the mash tun, we Vorlauf for 15 minutes. Then we sparge with 175&ordm;F water but it could take 30-40 minutes for the mash tun to reach 168&ordm;F. While the sparge water is being added, wort is simultaneously transferred to the boil. Some of the wort never reaches 168&ordm;F in the mash tun.
Sometimes, the mash tun is so full we can&rsquo;t even add enough sparge to get the temp to 168&ordm;F. So the wort never reaches that temperature until the boil. What I&rsquo;m not clear on is, what is the problem with this? I&rsquo;m assuming the sugar type and concentration would change, which would affect gravity.
If we are consistently hitting our target OGs (+/- 0.002), would the hot side still be the cause for variance in the FGs? Also, I&rsquo;m going to research Iodine tests a bit more
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It's fine that the MT jackets don't heat up. You would need a mash mixer and separate lauter tun for this. I've brewed on systems like what you're describing and understand the limitations. There's nothing "wrong" with the process necessarily, it might just produce more fermentable wort if/when enzymes are still present and able to do the work. &nbsp;
You're exactly right that the sugar type and concentration can change, which can also affect the FG. This has more to do with the malt's diastatic power (DP), or "enzymatic package" and its capability of breaking down more of the starches into simpler forms of fermentable sugars that the yeast can metabolize.</blockquote>
<blockquote>This can happen in a few different ways. The extract (OG) can be the same, but the % composition may be different depending on how much of both enzymes are present, which are activated, and when they're denatured. Yeast go after sucrose, glucose, and fructose, followed by maltose and then finally maltotriose, but not dextrins (unless it's STA1+).</blockquote>
<blockquote>The mash/collection/sparge controls will help determine the percent make up of each of these. This is what leads to different FG's. Below is an illustration of the compositional breakdown of wort (Kunze, 1996). 
<img src="https://imperial-yeast-cms.mur.io/assets/21b9e27a-6b3c-436a-b9dd-f89a9ae4185d?width=653&amp;height=545" alt="Case Study 005 Kunze 1996" />
An iodine test (starch conversion test) is pretty simple. Use a white plate, or dish, drop a few drops of clean wort from the mash (no husks) onto the plate, then add a drop or two of iodine. If the starch turns blue or black, there's still starch present. If it doesn't turn blue or black, there's no reason to hold the mash rest any longer.</blockquote>
<blockquote>The longer it takes to reach denaturing temperatures, the more fermentable the wort can become. Shortening the mash rest is just one control you have. Below are a few more. &nbsp;
The following controls may result in the following TG's:
High TG (less fermentable)= Thinner mash (high L:G), higher temp (&ge;156&ordm;F), lower pH (&le;5.3), lower DP malt (Munich, Vienna, oats, wheat, cara/cryst, DME etc.), shorter mash rest time (~30 min),&nbsp; early denaturing of enzymes (~170&ordm;F)
Low TG (more fermentable) = Thicker mash (low L:G), lower temp (149&ordm;F), higher pH (5.5), higher DP malt (Pilsner, 2-Row, rice, corn, dextrose etc), longer mash rest time (~60 min), later or no denaturing of enzymes (&lt;~170&ordm;F) 
Does this help? I'll do my best to answer them.
</blockquote>
Yes it does. Thank you for your help!

G03: Haze and Flocculation: Multi-knockout: Propagation

Hi. I have a question about <a title="G03 Dieter" href="https://www.imperialyeast.com/yeast-strains/dieter" target="_blank" rel="noopener">G03</a>. It&rsquo;s not flocculating and is super hazy. Do you know what might be causing this?
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That&rsquo;s strange, G03 should flocculate pretty well. Is this a fresh pitch, or a pitch that has been harvested? What&rsquo;s the batch size and original gravity?
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It&rsquo;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.
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Okay. So you&rsquo;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?
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Yes, we&rsquo;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&rsquo;s finished. We don&rsquo;t have a microscope and are not counting cells. I know it&rsquo;s not perfect, but it&rsquo;s how we&rsquo;ve always done it. 
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I&rsquo;m wondering about the amount of growth you&rsquo;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/&ordm;P. To achieve this in 5 barrels of 12.5&ordm;P wort, we&rsquo;d need to reach 7.7 trillion total cells during the propagation, before the final volume is added.
Under ideal propagation conditions, we&rsquo;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&rsquo;re describing however, I don&rsquo;t think we&rsquo;re achieving this growth.&nbsp;
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&rsquo;s difficult to say exactly what the cell count is without quantification, but in 24 hours you&rsquo;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/&ordm;P, a pretty significant underpitch.&nbsp;
When yeast is underpitched, they can experience a lot of stress, affecting healthy new cell growth and flocculation characteristics. I&rsquo;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&rsquo;d also add a yeast nutrient with zinc and magnesium, if you&rsquo;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.
</blockquote>
Thank you so much! I figured we were off, but I wasn&rsquo;t sure. We&rsquo;ve used pouches for a long time. Is it possible to order G03 in 0.5L sizes? What is the cost?
<blockquote>
No worries! Yes. 0.5L is our minimum pour size for in-stock strains. <a href="mailto:Customerservice@imperialyeast.com">Customerservice@imperialyeast.com</a> would be happy to help get pricing information and an order going for you when you&rsquo;re ready. Cheers!&nbsp;&nbsp;
</blockquote>

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