How do I lower my SG

It's not the number itself that's important (to avoid bottle bombs), it's that the number is stable between readings taken a few days apart.

 

How do you aerate your wort? I use US-05 for my ipas and almost all DME except for a 1/2 lb of corn sugar. For aeration I use to pour through a double lined metal strainer and paint strainer bag from kettle to bucket. Then I would swirl/shake the bucket for over 5 minutes. At that time I was getting down to 1.012-1.014. Now I use pure O2 and get down to 1.010-1.012. I also primary for 3 weeks and do as much as I can not to stress the yeast out during prep and fermentation.

 

Agree. If the gravity is still heading downward unbeknownst to you then you're going to get too much CO2 in the bottles. A couple readings that are the same, regarding of the actual reading number, confirms that your beer is done. You'll be okay since it sounds like you've taken multiple readings.

 

For a IIPA, replace ~ half of caramel malts with sugar, start fermentation at the lowest end of the band,...enjoy

 

What I do know is that Wyeast and White Labs propagate and package yeast via totally different means. I would never associate something that may be specific to one manufacturers operation to another. Consequently I would not conflate values that are published on one manufacturer’s web page with how another manufacturer’s product performs.

My conversation with Dr. Chris White, which I posted previously, indicated that the die off rate 21 billion yeast cells per month (used in the yeast calculator on Mr. Malt) was a conservative assumption. I have no reason to doubt what Dr. Chris White stated on this particular matter.

As another example, Wyeast states: “Our Product Warranty states that we guarantee the viability of the yeast in our Activator™ packages for 6 months from the manufacture date assuming that they have been properly shipped, stored and handled.”

If we consider a brand new Wyeast Smack Pack to have 125 billion yeast cells and that 21 billion yeast cells die off every 30 days (month) then after 6 months there would be absolutely no viable yeast cells (-1 billion yeast cells).

There is absolutely no doubt in my mind that a die off rate of 21 billion yeast cells per 30 days (month) is a conservative assumption.

Cheers!

 

Now we're getting somewhere. You object to Mr. Malty assuming a constant number of cells dying per month, rather than a percentage. But it does not do that. Mr. Malty predicts 76% viability at 30 days. And 55% viability at 60 days. After 6 months, it predicts 10% viability. So it's not a 'number of cells per month.' I honestly can't tell you what the whole curve looks like without doing a shitload of analysis.

But again I ask you...
White Labs says "After 30 days in the vial, the viability of our yeast is 75-85%, which is very high for liquid yeast." Do you believe this is reasonable or not? You can answer this question without regard to the actual number of cells the vial starts with.

 

“But it does not do that. Mr. Malty predicts 76% viability at 30 days. And 55% viability at 60 days.”

The Mr. Malty yeast calculator states that the number of cells decrease at a rate of 21 billion cells per month for the first 4 months. So from 1 month old to 2 months old there are 21 billion fewer cells. From 2 months old to 3 months old there are 21 billion fewer cells. From 3 months old to 4 months old there are 21 billion fewer yeast cells. If you want to know the percentage difference for the above:

• Month 1 to Month 2: a percentage difference of 32%
• Month 2 to Month 3: a percentage difference of 50%
• Month 3 to Month 4: a percentage difference of 98%

A percentage difference of 98% from a 3 month old package to a 4 month old package. Are you kidding me!?!

As I stated in my prior post: There is absolutely no doubt in my mind that a die off rate of 21 billion yeast cells per 30 days (month) is a conservative assumption.

Cheers!

 

Jack - I don't really have any data to support or deny this regarding yeast cells in hibernation. But I can tell you, as a cell culture biologist (by day), that the rate of drop off in viability of cells is very drastic and often non-linear. As the cells consume components, run out of those components, die, lyse, and release by-products into the culture that the living cells detect, more and more cells will die. It is not uncommon (at least in mammalian cell culture) to have viabilities in the 50-60% one day, and <10% the next, if the conditions are right.

 

Cell Culture Biologist?

/thread

 

I think I see why we're saying two different things. The calculator actually assumes you lose 4% on day 1. You are taking the calculation from that point to the end of four months? Then it is close to what you're saying for the first four months (after day one).

I happen to agree that when modeling the rates of yeast cell die-off, it may be more appropriate to assume a percentage of the remaining viable cells per time period. Which is what I do in BrewCipher, with the daily percentage being user selectable. I've also been combing the online literature for something definitive on this, but haven't found it yet.

 

Did I know you were a cell culture biologist? WTF! Any ideas about where to look for data on this question?

 

Missed this on first read. Where are you getting a 98% difference? In cell counts or in something else?

 

I can tell you that refrigerated yeast viability as a function of time is of absolutely no importance to anyone I know or work with in my day job...

My guess is that WL and WY - who are also cell culture biologists - are absolutely the experts in this field.

I have considered taking measurements to verify - I do have access to a microscope - but this is just not on my priority list - for the moment anyway.

 

The percentage difference of 98% is the between cell counts:

• Month 3 has 32.18 billion viable yeast cells
• Month 4 has 10.99 billion viable yeast cells

The percentage difference between the values of 32.18 and 10.99 is 98.17%.

Cheers!

 

“I have considered taking measurements to verify - I do have access to a microscope”

Matt, what is the uncertainty (accuracy) for performing a count of viable yeast?

For example, if you obtain a viable yeast cell count for a 1 month old Wyeast smack pack of x billion viable yeast cells, what ± y% uncertainty is associated with that cell count?

Cheers!

Jack

 

I guess I'll have to take your word for that.

 

Calculate percentage difference
between V1 = 32.18 and V2 = 10.99

( | V1 - V2 | / ((V1 + V2)/2) ) * 100

= ( | 32.18 - 10.99 | / ((32.18 + 10.99)/2) ) * 100
= ( | 21.19 | / (43.17/2) ) * 100
= ( 21.19 / 21.585 ) * 100
= 0.9817 * 100

= 98.17% difference

 

Ah. Difference. I was thinking about percentage change, which seems to me to be more appropriate when comparing a new value to an old value. But I get what you meant now.

 

Brett, as always, is the answer.

 

The percentage change between 32.18 and 10.99 would be 65.85% if that is a ‘preferred’ metric. Still, a huge difference from a value of 21%.

Once again I will repeat: There is absolutely no doubt in my mind that a die off rate of 21 billion yeast cells per 30 days (month) is a conservative assumption.

Cheers!