Rice Hulls: can you have too much?

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Nov 12, 2020
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Serious question. In the past I've struggled with gloopy mash when brewing big beers, so I started introducing rice hulls in order to make things flow a little better, reduce reliance on stirring, reduce HSA, improve clarity, etc.

Right now I'm mashing what will be a light Czech lager using some leftover ingredients and I've included 150g of rice hulls (3.5% of total grain bill) out of habit more than anything else, and the mash is flowing fantastically well; no need to stir, clear as a whistle, much faster through-flow than usual.

Already I know that there will be much less splashing / HSA as I raise my B40's malt pipe, the sparge will also be very brief, and I have to ask: are there any downsides to using plenty of rice hulls as long as your overall volume allows?
My understanding is yes. You don't want things to flow through your grist too fast as there has to be some level of soaking and absorption, but flow helps flush sugars out of the husks and into the wort so if its a thick sticky mash then rice hulls will help to promote flow and increase efficiency, but if you use them when you don't need them or use too many then you can actually reduce efficiency as you're just not getting the soaking and steeping. I think I read somewhere about an optimal flow rate of wort though the grist, cant remember the details now but it was in terms of total volume of water, so something like aim for a flow rate that ensures the total volume of water flows through the grain bed 5 times through the mash or something like that. Presumably any higher rate than that will negatively impact your efficiency.

Also important to realise that there is an absorbion of water from rice hulls so if you use too many then you'll increase your volume losses. You can pre-moisten the rice hulls before adding if you're not compensating for this from the beginning. I've never bothered as when I use rice hulls I'll typically use two large handfuls and see how I go, but even on the thickest mashes I've done when I've been aiming for gravities of 1.090+ two handfuls in a 20 litre batch has been sufficient with no stuck mashes or sparges..chuffing slow sparge (which is no bad thing), but not stuck.
Cheers for the response @hoppyscotty. Yesterday's brew day went pretty well and I was left with a pre-boil gravity of 1.042 against predicted 1.037, boil volume 28 litres against 28.86. Prior to using rice hulls regularly I played around with the grain absorption ratio in my calculations, and the 860 ml of difference could be down to the absorption or it could be just tolerance on my readings. I'm not too worried either way - adding some water to the boil would have likely closed the 5 point gap a little but in terms of mash efficiency I'm happy.

However your first point regarding flow rate intrigues me. I'm still very new to this hobby, and have been operating under the assumption that as long as the temperature and pH are OK then surely the idea is to get as much water through your mash as possible? I see it kind of like putting a rack of damp laundry in front of a dehumidifier: as long as the air flowing through the rack has less water content than the clothes, they will dry, and therefore the more air the better.

I'm now learning that the process of extracting sugars from milled grain is different, so I guess I need to better understand what it means to steep effectively. To be honest I have wondered for quite a while how you can have a well-flowing mash and a slow sparge when the two seem to rely on opposing consistencies. Interesting stuff.
The issue of flow rate intrigues me too but since I can’t measure it I just let it ride and judge it such that I maintain a consistent height of wort above the top of the grain so I know I have matched the flow rates.

There is certainly a benefit to enable movement and flow through the grist to help extraction of wort from the husks and to help insure all the starch within the husks is converted. Large mash tins have takes that continually stir the mash. Probably not needed on small scale but I think it would be most peoples experiences that when you are shooting for high gravities and efficiencies then periodic stirring of the grist through the mash is beneficial.

Also at homebrew scale then since the heat source is at the bottom of the vessel then recirculation is essential for managing mash temperatures. As always experimentation is the best thing to do to see what works best for you.
I can only agree with you about extra absorption (vol loss).

For the life of me I can't get why grain soaking and steeping would be affected.

This post might read negatively, its not, just never seen/experienced the need.

For me goopy = add water. Next time crush larger/adjust temps.
Probably not needed on small scale but I think it would be most peoples experiences that when you are shooting for high gravities and efficiencies then periodic stirring of the grist through the mash is beneficial.

All noted, thanks. I used to stir every brew every 15-20 minutes, partially in order to get a slow mash moving again, and partially because I wasn't happy with the way that my standard mash hat failed to distribute the wort evenly atop the grain. Since fitting an improved recirculation manifold I've been much happier with the wort distribution and I've also learnt about hot side aeration, two factors which have pushed me towards not stirring at all, and instead trying to keep things flowing by adding more rice hulls - not that stirring would be particularly easy now with that manifold in the way. As a bonus I'm experiencing significantly clearer pre-boil wort, though as I usually cold-crash anyway I doubt there's much benefit there.

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