To those of you with motorized rakes in the mash tun, do you ever stir the mash after the sparge has begun? Or would agitating the mash at higher temps (sparging at 176-178F) release tannins or somehow oxidize the wort? Also does stirring increase efficiency noticeably?
I'd be very interested in an answer to this question as well.
I'm about to start brewing on a 20bbl. system that has had it's rakes removed.
Apparentley,....the previous brewer found them more of a hassle than a benifet.
Really depends on your system, typically on smaller systems you dont need one (20 bbl or below) they can be a problem. but yes, you do want to turn the rakes very, very slowly (approx 1 or 2 turns every 20 minutes) and you want to have them about 6-8" above the grain bed. This will increase your efficiency! I dont advise sparging at highier temps 169-170. The problem with some rakes is after you raise them above the grain bed (6-8"), they will drop down and break up your mash bed then some because of the weight of the grain and water the motor is not powerful enough to raise them again. My experience with them was a good one, but only on systems 50 bbls and bigger, never on a small system. Hope this helps!
Rakes in a Mash Lauter
The information in the above reply is good. I have worked with rakes on system of 20 bbl. and larger. My experience is that using rakes on a system less than30 BBl is not required, but the the reason for the rakes not working on smaller systems is related to there design. Equipment manufactures tend to try and make systems that stir and rake, but I haven't found one that worked well at both yet. In fact the raking process is very touchy and any force applied downward on the bed will tend to stick the run-off. The rakes should be knives that cut thru the bed and allow water to reach the part of the bed that hasn't had the wort completely rinsed out. Take a good look at your machine, and if you can get someone in your neck of the woods with more expirience to help, do so. I like 171 its really bepends on your preferrence but raising the temp to high will extract unwanted flavors.
do you think boiling the wort would boil out the oxygen !
Thanks for all the replies. I am mostly worried that the physical agitation of a mash during sparge might somehow aid in the unwanted release of tannins into the beer. I have heard that keeping the sparge water under 180F is essential, but it sounds like most people sparge lower at 170-172F. I will try lowering the sparge temp, and quit stirring the mash.
In response to oxygen being removed by boiling...yes so it would seem, but then why do we all make a huge deal about hot side aeration?
I had always considered that HS aeration was happening after the boil, but maybe that doesn't make much sense either. I've heard some say it's a myth.
Let me ask this question: What is the flavor produced in beers with a HSA problem in the process? Oxidation? Cardboard?
HSA is fact, not myth. Oxygen is highly reactive to organics. Although boiling is a good way to flush most O2 from WATER, it's apples and oranges with WORT. Raising the temperature, and even boiling just makes the kinetics of oxidation happen quicker and more surely. Avoid splashing and sloppy transfers. Calm, gentle, controlled wort handling makes better beer.
That apples and oranges description makes some sense to me. There's really nothing to oxidize in water, though it can certainly take on Dissolved Oxygen - which may then be boiled off. The non-water portions of the wort are what see true oxidation, not easily reversible. I'll buy that. The question then for me is one of severity, and net effect.
So, what's the effect on the finished product?
Rakes and knives
I found that even on smaller systems (15bbl) mash rakes are beneficial. The design problems noted may hold true but the system I used worked quite well. The motor was variable speed and reversible. Cutting was always above the bed as they were fixed 6 inches above. Reverse was used to grain out, with "feet" that scraped only in that direction. After moving to a 10bbl system without them I found 8-10% decline in efficiency. 8 to 10% less malt per year certainly will pay for the extra equipment cost.
I worked on a 20 bbl system for six years and can recall very few instances when we did not run the rakes, at least once, during the sparge. We got increased efficiency and never seemed to get any negative effects from doing this, although some brewers seemed to be horrified that we were running the rakes during sparge without reverting to another wort recirculation to clear the wort again. Our rakes (DME) could not be raised to clear the false bottom, so we always got some hazy wort transferred to the kettle during this operation. Our beers won 5 medals in national and international competitions (i.e. GABF and World Beer Cup) in a four year period, so if we were doing something wrong it never showed up in the finished beer.
If you are worried about negative effects to your beer from running the rakes during sparge I would suggest doing comparisons between identical batches in which some have not had the rakes run during the sparge and some that have. Whatever you decide to do it will probably not agree with what some other brewer is doing. Remember that old axiom, "If you ask ten brewers the same question you will get eleven different answers". Go for it - all good brewers do not agree on process procedures.
I've never used a mash-tun with rakes, and the one I'm about to use for the first time(20bbl.), has had them removed.
The recirc port comes in on the side,rather than from above the mash, so I see the potential logic in "shallow-slow rakes" to re-distribute the incoming wert.
In other words....I think I'll re-install them.
HSA and tannins
HSA and tannin leaching are going to be related to factors other than stirring per se. Tannin leaching is going to have a lot more to do with the pH of the wort which, of course, will be rising during the sparge. As long as you don't go above, say, 5.8 you should be fine, stirring or not.
As for hot side aeration, you need to take the same precautions not to shear the wort or incorporate air that you do throughout the rest of the mashing process. While boiling does remove oxygen from the wort, the problem is that HSA reactions happen quickly enough that the damage is already done to wort before it comes to a boil in the kettle. Be gentle with your wort.
So as long as you're following good mashing and sparging practices already (correct pH, gentle wort handling, etc.), the question of stirring or no is going to have more to do with wort clarity and efficiency questions. In general, raking is worth doing if your system can do it well and still run basically clear worts. If your system can't rake well (or at all), you don't really lose anything but a bit of efficiency. As others have already said, you really want to cut the grain bed, not stir it. If you're mixing and not cutting, you're going to need to recirculate to clear the runoff and you're really just moving to a batch sparge/ parti-gyle system rather than the continuous sparge method raking is supposed to accomodate. A final caveat: if the crush on your malt is not very good to start with, you're more likely to extract undesirables, especially at higher temps--probably better to be extra gentle with the grain bed and not rake or stir.