Mash tun efficiency

[Pharmbrewer]

I have recently noticed with my higher gravity brews my efficiency goes down. I use a 62 quart "cube" cooler with a cpvc manifold in the bottom as a mash tun. Recently I noticed that I may have in fact reached a saturation point for a certain volume of wort. i.e. I usually collect about 7 gallons of wort, boil for an hour for 6 gal in the fermenter. For higher gravity beers I usually continue to sparge and get another 2-3 gallons of a lower gravity beer. Sort of a backwards party-gyle. I recently made a barley wine and added grain compaired to my last high gravity brew in order to increase the gravity. I was quite suprised when my OG came out exactly the same as my last high gravity brew despite having added 2 lbs of base malt, however my second runnings did yield a higher gravity than the last. I know the solution is to sparge more and boil longer or add DME, but I'm curious if anyone else has noticed a "saturation point".

My hypothesis is that for a given amount of water one can only rinse so much sugar out of the grains and at some point the addition of grains does not result in a more concentrated wort due to the inability of the sparge water to rinse the grains. I feel this saturation point would be dependent on mash tun geometry. i.e. my mash tun being taller would have a lower saturation point due to a "longer" grain bed that the wort must travel through. Of note my 10 gallon mashes which use roughly the same amount of grain as some of my high gravity 6 gallon brews do not suffer from decreased efficiency. Oh and I typically batch sparge.


Any thoughts on this?

[ziggy]

I think you are on the right track. The two variables that you have to consider with sparge efficiency are time and concentration gradient. If you drain your first runnings, add sparge water, let it sit for 30 minutes, then drain it you will extract more sugar than if you just added sparge water and let it run straight through.

In the case where you added 2 pounds of grain, if you had the same mash thickness you would have the same sugar per volume after running off.

You can inprove your MASH efficiency by making sure there is adequate calcium, increasing the time, and making sure the pH is spot on. That and a finer grind size will give you optimal conditions for the enzymes to do their work and extract more sugars per a given volume.

You can try reiterated mashing where you mash new grains with your runnings from the previous mash. There's a BYO article on it somewhere.

If you are trying to figure out the economics of whether or not you should buy a taller mash tun to get mroe efficiency I would say that it's probably not worth it. Extending your soak time on the batch sparge would probably get you about equal to having a taller mash tun. If you were fly sparging it would be a differnt story.

[Pharmbrewer]

Arrgghh! I'm an idiot. I'm batch sparging with more water than I need in order to get that extra couple gallons of a lower strength beer. So the concentration of sugars in my sparge water is going to be lower due to the extra water. therefore the difference I expecected in gravity was diluted out over the 2 beers. The gravitys being the same in the barley wine as last time was probably just a coincedence. I'll have to sparge with the exact amount of water that I want for my big beer next time and see if this makes a difference. Thanks ziggy your comment about concentration gradient that made it click.

PB

[noremorse1]

I think the biggest factors that influence mash efficiency is time, temperature, mash thickness and the mash tun itself. There have been some great studies on this. One of the best I have seen was done in 2008 by Kai Troester at braukaiser.com
http://braukaiser.com/documents/Effects ... ciency.pdf

He concludes that there are a lot of important factors but, the two that a homebrewer can control the best, are time and temperature.

[Bugeater]

I always have the same problem when I do big beers if I don't change my process a little. Increasing the amount you sparge makes a big difference. Once the sparge water gets saturated it can't remove any more sugar. For my big beers (I do a couple different ones at 1.100+) I plan for a 90-120 minute rapid boil. The rapid boil increases my boiloff rate to 1.5-2 gallons per hour. I make the appropriate adjustment to my preboil volume to allow for the extra boil off and then I split the sparge into two equal batch sparges. There will still be plenty of sugar in the mash after the first sparge that you won't need to worry about your gravity getting too low. By the time you finish the first batch sparge, your grain bed will have lost quite a bit of temperature so your second addition of water should be in the 180°-190°. This won't raise the temperature of the grain bed enough to create any problems but will make extraction of the remaining sugar easier.

Wayne

[Pharmbrewer]

I always have the same problem when I do big beers if I don't change my process a little. Increasing the amount you sparge makes a big difference. Once the sparge water gets saturated it can't remove any more sugar. For my big beers (I do a couple different ones at 1.100+) I plan for a 90-120 minute rapid boil. The rapid boil increases my boiloff rate to 1.5-2 gallons per hour. I make the appropriate adjustment to my preboil volume to allow for the extra boil off and then I split the sparge into two equal batch sparges. There will still be plenty of sugar in the mash after the first sparge that you won't need to worry about your gravity getting too low. By the time you finish the first batch sparge, your grain bed will have lost quite a bit of temperature so your second addition of water should be in the 180°-190°. This won't raise the temperature of the grain bed enough to create any problems but will make extraction of the remaining sugar easier.

Wayne

Thanks for the advise. I'll try splitting up my sparge next time. I try not to extend my boil if I can help it. I brew in my basement and it can get quite humid sometimes. One of these days I'll bite the bullet and install a hood.