Carbonation Calculations - 2nd Opinion Req Pls!

[naturals]

So ever since I've installed a fermentation fridge I've had real trouble hitting the right carbonation levels.

The ten or so batches I've done have all come out extremely undercarbonated - even left in the bottle for six months they never achieve the carbonation they should. Because of this I think it's an "amount of sugar" issue rather than a yeast problem. My process is to ferment at usual temperatures (18c ish for ales), ramp up to 25c to ensure carbonation is complete, then crash cool. I batch prime so dilute the sugar in boiling water, add to my bottling bucket. Rack off from my FV then give a solid stir to make sure the sugar is evenly distributed. I tend to chuck the bottles back in the fermentation fridge at around 25c for a couple of weeks, then leave at room temperature for a week or two before drinking.

My current batch is 20 litres of lager, brewed with lager yeast using the Brulosophy technique. Highest temperature achieved during fermentation is 20c and I've crash cooled to 0c. Looking at a carbonation level of 2.7 volumes, the TastyBrew online calculator reckons I need to carbonate with 142g of table sugar. Beersmith reckons 150g. I've run it through a whole heap of other online calculators, all of which are somewhere between the two.

Can anyone shed any light on how much sugar *they* would use? I've read so many posts saying "use the amount of sugar you need, not what the calculators tell you". On this basis I was thinking of adding an extra 20g or so as I know the online calculators are inaccurate for what I'm doing. I don't want bottle bombs but equally it's starting to suck drinking flat beer all the time!

[BrannigansLove]

I use the Brewers Friend one, that says 147g for the values you've provided.

[naturals]

Thanks BL. Rounded it up to 160g to be on the safe side. Hopefully no bottle bombs and a bit more carbonation than before.

[Sadfield]

Here is the formula to calculate it yourself, as supplied to me, from one of the brewers at Thornbridge.

[Matt in Birdham]

I'm surprised that your beers are "extremely undercarbonated" with those sugar volumes. Even if you're not hitting 2.7 vols, you should be getting pretty close - and the beer should definitely be fairly well carbonated. Your process sounds fine - that's exactly what I used to do when I bottled - so really I have no idea what is going on. I'm just not sure that the answer is to throw more sugar at it.
Incidentally, as far as I know (and for sure, in the version I am running), Beersmith only gives sugar weights for dextrose and malt in its carbonation calculator - which would explain the higher value you got (you need more dex than sucrose). ~150g of sucrose in 20l is a decent whack of sugar - does it taste sweet at all as well as flat?

[naturals]

They came out ok - maybe a little on the sweet side but certainly a lot of fermentation had happened since the bottling bucket. It's kinda hard to say as the last batch was the first milk stout I've done so was naturally sweet anyway.

Say it was a problem with the yeast not fermenting out all the sugars - how could I prevent that? I'm careful that even when I've crash cooled I churn up a little bit of yeast into the bottling bucket. I also try to turn the bottles upside down a couple of times during fermentation to ensure the yeast doesn't stagnate too much.

Any other tips?

[MTW]

Your method sounds secure. I do pretty much the same. I don't tend to take the ramping past 23C though. You condition the bottles at the same temperature as the ramp, which I think is good practice, as some yeasts may get lazy once they've been that warm and work much slower at anything cooler. That said, it may still be worth limiting the ramp a little. 6 months is certainly a long enough test and clearly anything that was going to happen would have happened by then, even at lower temperatures. If they're evenly carbed within the batch, then the distribution sounds even too.

I recently just primed 20L of hefe with 180g sugar and it is nice and fizzy. It had reached 23C during primary. 2-3 weeks warm and a day or two in the fridge was all it took for the test bottle to be ready, and the subsequent batch has been identical. My previous hefe had 140g and was undercarbed for the style.

Having primed many Belgians as well, I think it should prove hard to have a lack of high carbonation around 9g/L.

[Matt in Birdham]

I think lack of yeast is very unlikely to be the problem. I have done lagers in the past that lagered for over a month (and crystal clear at bottling) and carbed without additional yeast. It took a long time, to be sure, but less than 6 months.
Your caps couldn't possibly be leaking a bit of CO2 could they? Not that I've ever heard of this happening. Mysterious.

[naturals]

I don't think it's the caps; they're all fairly recently purchased (a few different suppliers too) and since the carbonation issue is the same across the whole batch (in fact, the same across many batches) I would expect a bit more irregularity.

The only thing I can think of is that my STC needs calibrating (i.e. that rather than fermenting up to 25c it's actually fermenting warmer and forcing more CO2 out). That said I have a second thermometer in the fridge to measure the ambient temperature and it seems to correlate.

[Sadfield]

Do you ferment under airlock? How long at 25C before crash cool? Wondering if you have very little residual co2 in your beer before crash cooling, and little co2 above it, that can be reabsorbed.

What temperature is the beer when you prime it?

[naturals]

Yeah, I ferment under an airlock and leave it on when I crash cool.

I'll generally ramp up the temperature and leave it there for around a week.

Crash cooling, I normally go to 4-5c (lower for a lager). I take the beer from the fridge, leave it to settle on the side for around an hour, transfer to bottling bucket then bucket. At a guess maybe it would gain a degree or two during that time? That'd put it at around 5-6c ish when primed / bottled.

[Sadfield]

I'll generally ramp up the temperature and leave it there for around a week.

Quite a considerable amount of time at 25C, then, which would have quite an impact on the residual co2. For the 10 under-carbonated batches, was 25c the figure used when calculating the priming sugar in TastyBrew/Beersmith? It seems that it is a homebrewing point of contention between Fermentation Temp and Temp at bottling, that should be used in the priming calculation. Either way, you have a considerable difference between 7c and 25c.

[naturals]

I've read a lot on whether to use the fermentation temperature or bottling temperature. Personally I've always used the maximum temperature experienced during fermentation (so 25c) when calculating the sugar additions. Using the bottling temperature would give a smaller sugar addition so would only exacerbate the issue.

It was interesting what you said about CO2 reabsorption during crash cooling. I didn't even realise CO2 was reabsorbed. Maybe I'll have to look into this and check enough air is getting back through the airlock.

[ManseMasher]

I tend to carbonate at the same temp as I fermented at, and never had any issues? I follow the 2 + 2 + 2 rule - 2 weeks fv, 2 weeks same temp as fermentation, 2 weeks cooler. Always get good carbonation. I use brewers friend (about the only useful calculator I have found on there).

[MTW]

I've read a lot on whether to use the fermentation temperature or bottling temperature. Personally I've always used the maximum temperature experienced during fermentation (so 25c) when calculating the sugar additions. Using the bottling temperature would give a smaller sugar addition so would only exacerbate the issue.

It was interesting what you said about CO2 reabsorption during crash cooling. I didn't even realise CO2 was reabsorbed. Maybe I'll have to look into this and check enough air is getting back through the airlock.

Everything you've said just sounds like what I do, only I've added 9g/L where you added 7g/L approx, excepting a 2C difference between our top temps. If you prime at 9g/l for the fizzy ones, I'd be surprised if that doesn't solve your problem. Then you can just keep things consistent from thereon, which is ultimately the name of the game for this: the calculations will only get you so far.