Superefficiency with Stovetop BIAB?

[basswulf]

I've been brewing in relatively small volumes using BIAB approaches - typically I'll get about 6l beer out of the end of the process. Over the last year or so, I've been using the excellent recipes in Wheeler's Brew Your Own British Real Ale book and getting some very satisfactory results. I've tended to find that my original gravity reading is a few points higher than the recipe, which I've put down to having the grains floating (in the bag) in the full volume of water all the way through the mash.

I've recently added another tweak to my set up. I'm using a device called a Codlo (essentially a temperature linked power controller with timer) to control a slow cooker. This means I have to break the mashing into several batches because of the limited capacity of the crockpot but I can set the temperature and timer and leave it to get on with 90 minute mashes that stay very close to the desired target. The liquid from each batch, including bag squeezing is added to my 13l stockpot and covered with a lid while sitting - I figure that, starting from a sanitised base and boiling for 90 minutes afterwards should minimise infection problems. Half an hour at 63°C is enough for vat pasteurisation so 90 minutes at 67°C means it comes in clean. After mashing, I got the wort to the boil with the lid partially on and then kept it boiling for 90 minutes with the hop additions. I then transferred the wort into a plastic jerry can to cool overnight but also separated some off into a metal goblet, covered with cling film, to cool down more quickly and let me take a gravity reading.

The recipe was Bank's Hanson's Mild (p90 in 3rd edition) and the target OG was 1.035. Somehow though, I seem to have hit 1.060! That might be bumped up a little because of a certain amount of sediment in my sample (although the reading didn't change even when it had time to settle in the sample tube and I don't know how the solids would affect buoyancy compared to dissolved sugars). I wonder also if it is because I didn't raise the temperature of the resting wort (mash out) and so enyzmatic action may have continued for over three hours in the first batch (I did 3 * 3.5l) and 1.5 hours in the second.

I will take another reading when I siphon it into the fermenting vessel tonight but am surprised by this apparant super efficiency. Scaling the recipe slightly increased the proportion of pale malt to water but only by about 4% (I'd have used 1454g pale malt to 10.51l of water if being precise in my scaling but rounded it to 1500g pale malt to 10.5l in my actual recipe). Any thoughts?

Also, while I'm tempted to dilute it a bit, increasing the fermenting volume, I'm wary of trying to bring it anywhere near 1.035. Wheeler's book notes that mild ales used to be brewed much stronger than is the current practise (in fact, I had originally thought about Wheeler's Sarah Hughes Dark Ruby recipe, which has a target OG of 1.058) so I'm pretty sure that I'll get something at least drinkable and probably rather enjoyable at the end. However, I'd like to get a little closer to the targets, especially if it is only a case of raising the collected wort temperature by a few degrees at the end of each batch.

Cheers,

Wulf

[brewnaboinne]

I had BYOBRA in my hand when I saw this post. I think you scaled the 19l recipe by 0.55 ? I'm not sure I understand that as you say that you normally get 6l out of the process, your FV must be about 6.2l ? Or was this a bigger brew than normal ?
I think Graham Wheeler used his Beer Engine to write those recipes so if you play around with that ( in extras above) it might help. It so happens that if you put in a brew length of 6.2l an OG of 1060 comes out at mash efficiency of 85% with 1500g pale malt.
His default efficiency is 75% but you may well be bettering that . However you must have made a mistake in the calculations.
I believe the brewlength in the recipes refers to the volume in your FV not how much you actually drink though someone may correct me on that. Hope this helps, a BIAB fan might be able to help more.

[basswulf]

0.553 - pretty close. Based on the capacity of the mashing vessel (slow cooker), I adjusted to get as close as possible to 10.5l water (or 3 x 3.5l for my batches).

That's the water input. Losses occur along the way - a small amount with the grain (although I squeeze that pretty well), more with the boil and then more at each stage as I transfer between vessels (copper -> jerry can -> fermentor -> bottling bucket -> bottles) and leave behind the settled sediment. Truth be told, my stock pot serves as my copper and fermentor and the jerry can doubles as a "bottling bucket" but the principal works the same.

I should double check Wheeler's process. As I recall, his default option is all grain with sparging; I suspect he uses some of the initial liquor for the boil and the rest to sparge but I can't remember for sure. I think my technical "brew length" would be 10.5l which, grabbing this online calculator, puts me in the >100% efficiency category. I must have mismeasured the grain or water somewhere along the line.

I am still intrigued to find out what difference the long rest makes to the post-mash wort. Meanwhile, I'll try the recipe again before too long and be doubly careful on all the measurements.

I was using Young's Pale Malt for this, with quite a high proportion of flour-like powder among the grains; I don't know if this would be another factor in increasing the amount of sugars I got out.

Wulf

[brewnaboinne]

No your brew length is what you put in your FV. The 10.5l is your total liquor compared to 26.3 in Wheeler's recipe, that's the real difference. It's possible you got a slightly more efficient mash, but not by that much. Doubt that it's got anything to do with the malt.
Cheers

[basswulf]

That would have the brew length at about 9l then but that still doesn't make sense for the apparent efficiency. The malt was scaled down with the same conversion factor as the liquor but then rounded up a little. I need to double check the hydrometer and measure more carefully next time. Meanwhile, this brew is now underway with the yeast. It probably won't be much as a clone but I'm hoping it will be decent as a beer.

Thanks,

Wulf

[brewnaboinne]

The main thing is you've got some beer on the go!

Cheers

[rpt]

I've sometimes found that the gravity reading I take after the mash (BIAB in a 40L Buffalo) can be much higher than I expect, but once I've done the boil it is more sensible. Did you take another gravity reading when you pitched the yeast?

By the way, it is possible to have a mash efficiency >100%! You are calculating how much sugar you got out compared to how much sugar is in the grain. But how is the latter worked out? It's done in a laboratory with standard conditions - grain crush, water ratio and temperature etc. So if, for example, you finely crush your grain you might actually be able to get more out than the lab did.

[basswulf]

Getting >100% efficiency compared to the lab readings makes sense. However, I'm not sure how the boil would make the gravity reading more sensible - unless you are adding further water before boiling.

The reason I'm checking back to the thread is that I've had another stab at the same recipe and, while not hitting quite the same heights, still got an OG well above the expected 1.035. This time though, I only boiled for 60 minutes rather than 90 (inspired by an experiment on boil length from brulosophy). It struck me that, because I'm brewing a scaled down recipe but the rate of water loss to evaporation remains the same, my c.10l wort is losing about 30% of its water (I was left with 7l after an hour's boil) while a 23l attemp would only lose about 13% (assuming the same kettle diameter). That would fit the pattern that my 90 minute boil (from 10.5l intial water) came in at an even higher gravity. A larger pot, for a larger volume, would lose more for the same length of boil due to the increased surface area but I think would still leave the starting volume as a significant factor.

Does that sound like a convincing explanation? If not, at least I've still got another brew going...

Wulf

[Redimpz]

Efficiency is all well and good if you are on a budget or a huge brewer making thousands of gallons a year, but for the home brewer it is not really relevant other than a measurement and bragging rights.
The important thing is that you've successfully made beer.