Gravity points per volume of pressure?

[Kieran]

I've been doing some googling and forum searching and managed to find only partial answers to this question. Approximately how many gravity points of honey equate to one volume of pressure in a 12 oz beer bottle?

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[darigoni]

I think the best info you are going to find is in the online beer priming calculators, which there seem to be quite a few of.

http://www.homebrewing.com/calculators/?page=tools&section=sugar

 

[Kieran]

Ok, so figuring that 3.45 lbs of honey produces about 135 points per gallon, that means that there are about 2.5 points in 1 oz. Using the calculator set to 70°F and 1 gal, 3 vol would be (approximately) 4.25 points of honey. Does that seem right?

Follow up question, do you start counting that from 1.000 or below that?

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[Maylar]

The beer guys say that typical carbonation of 2.5 volumes CO2 at 70°F will consume 2.3 points of sugar.

 

[Kieran]

The beer guys say that typical carbonation of 2.5 volumes CO2 at 70°F will consume 2.3 points of sugar.

So would that mean roughly 1.000 after priming (starting from really dry) or roughly 1.002 after priming (start counting at 1.000), assuming the yeast don't hit tolerance?

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[Maylar]

It's obviously a prerequisite that gravity be stable, but yes a couple points above wherever the ferment stopped. The priming sugar calculator at Northern Brewer works very well and lets you pick what sugar to use:

http://www.northernbrewer.com/priming-sugar-calculator/

 

[Kieran]

Thanks all, I have a clearer picture now.

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[bernardsmith]

Yeah...I don't think the issue of priming and pressure has anything to do with the final gravity. The issue would be as Maylar suggests that the gravity you have is rock solid stable. If you add a known quantity of fermentable sugar (very approximately 1 scant ounce per gallon) and there is active yeast then IF the gravity meant that no further fermentation was taking place absent this addition then the change in pressure would be due only to the gas produced by the added sugars (approximately 2.5 volumes). That said, my imagination is quite limited in that I cannot imagine how you could have a high gravity that was both stable and would allow you to prime by adding sugar: either you have eliminated the yeast (one way or another ) and so no priming could take place or you have not eliminated the yeast and if they can ferment the added sugar then there is nothing to prevent the yeast from fermenting the residual sugars. With beer you are dealing with unfermentable sugars from the grain - sugars that the yeast cannot break down, so if you add fermentable sugar (corn sugar, for example) then the yeast can consume that, but with mead , unless you are talking about a braggot the sugars are fundamentally all accessible to the yeast.

 

[Maylar]

Which implies that the mead needs to be as dry as the yeast will take it before priming. Trying to carbonate a mead that's exceeded its alcohol tolerance is not going to work.

But why any given yeast will finish at 1.000 sometimes and 0.996 other times is a mystery to me. I've had S-04 quit anywhere between 1.000 and 1.004 but it always carb'ed up after priming.

 

[Kieran]

It was really more of a hypothetical that would be a bad a idea to try. A curiosity. My thinking was that if you have a mead that is still fermenting but almost done, could you bottle it and get a predictable level of carbonation. It seems the variation in yeast quitting points to too much of an issue for it to work though. Too risky; like I said, it was more of a hypothetical.

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[Kieran]

It was really more of a hypothetical that would be a bad a idea to try. A curiosity. My thinking was that if you have a mead that is still fermenting but almost done, could you bottle it and get a predictable level of carbonation. It seems the variation in yeast quitting points is too much of an issue for it to work though. Too risky; like I said, it was more of a hypothetical.

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[bernardsmith]

Which implies that the mead needs to be as dry as the yeast will take it before priming. Trying to carbonate a mead that's exceeded its alcohol tolerance is not going to work.

But why any given yeast will finish at 1.000 sometimes and 0.996 other times is a mystery to me. I've had S-04 quit anywhere between 1.000 and 1.004 but it always carb'ed up after priming.

S-04 is a beer yeast and that may mean (merely hypothesizing) that it may dis-prefer certain sugars available to it. I believe that all yeasts go after glucose first and then fructose and then (I think) sucrose. Honey contains some maltose but wine yeasts (I understand) unlike yeasts cultivated for beer are unhappy with maltose so I would have thought that S-04 would be better able to ferment honey until it was brut dry...But your point about S-04 being unable to finish the job rings true - as many cider makers who use S-04 use it because they are looking for a sweeter finish... So what is with that ale yeast?

 

[Maylar]

I should have stipulated that my experience with S-04 is with cider, not mead... but still the same question applies. Why would something with fully fermentable sugars finish dry sometimes and other times not.

 

[bernardsmith]

That, I think is a really good question. Just speculating (and I do not want to hijack this thread - ) but I wonder if this has to do with how and when yeast flocculate (I love that word - flocculate). If a yeast has a tendency to flocculate before all the sugars are fermented then their clumping and dropping out of solution will prevent the fermentation from being completed -even in the presence of perfectly fermentable sugars.*

Brewers measure and invoke "attenuation" rates (or apparent attenuation rates) for the yeasts they tend to use whereas wine makers (and mead makers) don't. Clearly, brewers work with sugars that are not fermentable and they can expect their beers to finish with gravities 10 points and higher, but wine makers don't ordinarily "expect" their wines to finish sweet. We have to work to ensure that some residual sweetness remains otherwise we can count on a wine fermenting dry. Are "wine yeasts" then always late flocculators and SOME beer yeasts (like S-04) early flocculators and could that explain why with some yeasts some of the simple sugars are left unfermented?

* Lager yeasts tend to gather low in the carboy whereas other ale yeasts in some way make use of the CO2 to work closer to the surface. Might there be some types of ale yeast that tend to gather lower (not at the bottom, but lower in the fermenter than others) and might they tend to flocculate sooner?