Problems with base malt in silo

TrailwayTom

Hey all! Over the past year I've been having consistency issues with silo base malt and can't figure out exactly what's going on...
My brewery uses a ~30,000 kg malt silo to store our base malt (Pilsner from Canada Malting Co), we've had it for about 4-5 years. To measure malt for each brew we have compiled a sheet with heuristic flow rate data which is reasonably accurate; however, once the silo drops below the halfway point the starting gravities of my brews drop off significantly. At first I thought it was an issue with flow rate, and while it does see a slight drop as the silo empties, it's never more than 5-10%, which I will account for by running the auger 5-10% longer.
Before the latest silo refill I inspected the grain being pulled before running it through the mill. Our grain has always been incredibly dusty, but I also noticed a very high proportion of husks and broken pieces, and the starting gravity of that batch was 20% lower than average, I've had similar efficiency issues with the last 6-8 brews. Is it normal for this to happen with the last few thousand kilos of grain in a silo? Has anyone else had similar problems?
I suspect this may be a supplier issue- either we're getting poor quality malt to begin with, or the silo is being filled too aggressively and it's breaking up some of the malt before it hits the mill which leads to settling issues in the silo.... I'm just trying to get some guidance before I contact my supplier to raise my concerns with them. Can anyone offer any input? Thanks!

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dick-murton

What size is your setup, i.e. how much base malt is used for a typical brew and thus how long between re-fills?  Do you inspect the malt each and every time you get a delivery?  Do you hold a representative sample of the grain taken as it is off loaded.  Unless you have a trickle sampler, take samples at different points during the run and compare each of them, and against a sample your supplier should be providing.  My immediate suspicion is that you grain handling system is damaging the malt, though why it should be particularly during the latter part of a deliver I have no idea.  

TrailwayTom

We brew on a 10 BBL DME brewhouse, we typically use ~250 to 300 kg of base malt per brew when everything is working as it should. I do a visual inspection of the malt every time I mill for a batch, but when we get a refill (every 2-3 months) there's usually still a few thousand kgs of grain left in the silo so it takes a couple more weeks to start pulling from the fresh grain. We're provided with a sample of grain after every refill, but the sample is always in much better shape than what the auger pulls from the silo at the end of a silo fill. The refills usually happen after hours when the brewing staff is gone for the day, so we don't usually get to inspect it before or during the refill, the truck driver just leaves paperwork and a sample taped to the silo.
Thanks for the suggestion on sampling, I actually decided to start pulling samples periodically to see how they compare to each other and to the supplier sample. I'd be surprised if it's our system that's damaging the grain though; if that were the case I'd expect the grain to be consistently beat up, and not see so much variance between pulling from a full silo versus an empty silo.

dick-murton

I suspect in that case at least part of the problem is the long storage life you are subjecting the malt to. Most people seem to get a new delivery of the base malts at least every 3 to 4 weeks, at least partly because of storage space and lump sum cost of large deliveries compared to smaller one, but also because the malt tends to be more consistent across a delivery batch and between deliveries (there will always be exceptions of course, and here I am thinking particularly about small breweries in say the tropics.)
It is possible the malt enzymes have degraded sufficiently during storage so conversion is poor. If the general humidity is high, then although I assume the silo is covered and proof against direct rain ingress, the upper layers will absorb some moisture which will exacerbate the denaturing of the enzymes. Alternatively, and not knowing what your ambient conditions are like, but this seems more likely, it could be drying out and during milling the husk is shattering more due to the low moisture content. Can you do a moisture test on say a weekly basis and see how or if the moisture content varies?  
Found this abstract
[COLOR=#e74c3c]The effects of storage temperature and moisture content on amylase activity of malt were investigated. Three different malt samples with initial activities of 136, 141, and 150 SKB units per g (dry basis) were stored for a period of 3 months in a freezer (-18

dick-murton

If you have a set of ASBC sieves - Aperture sizes: 2.00, 1.40, 1.00, 0.50, 0.25, 0.18, 0.15 mm.
Husk volume
The volume of material V, found in the 2.00 mm sieve needs to be corrected to a nominal 100g amount. This is done using the formula:   Husk Volume = (100 / M) x V ml  
Express Husk Volume to the nearest 5 ml
You will find various statements about the ideal husk volume should be.  Obviously this varies somewhat with the mash extraction method, but a typical value we aimed for for was > 450 ml / 100 g for lauter tuns, though you will see target values as high as 600 ml.  The main thing, as with all grist analyses is getting the values consistent and then fiddling around with the mill system to improve the extract - crudely for a mash or lauter tun - high husk, low flour and large grits, but lots of small and medium grits.

TrailwayTom

I just read the full abstract of the article you referenced, and based on that I don't think it's an enzyme issue. The abstract goes on to say that "Under all storage conditions, the loss in amylase activity was less than 10% after 3 months." A 10% decrease in amylase activity wouldn't affect the conversion that significantly. As a sanity check for this theory, starch conversion tests are normal and all terminal gravities are consistent, give or take a gravity point. Our malt spec has the diastatic power listed at 145 for the most recent crop, so even a 50% reduction in diastase enzymes should still leave enough for full conversion.
I also don't see it being an issue with the mill gap setting, as the efficiency issues directly correlate to the amount of grain in the silo and will vary up and down with each refill despite the mill gap staying the same.
Another member here PM'd me suggesting it's just a buildup of husk material in the silo combined with flow channeling of the heavier grain particles. He experienced this issue in the past and had to start fully emptying the silo before a refill, which fixed the issue. We never completely empty our silo, so it's quite likely this is the case as more and more husk material is allowed to build up. Before the next fill I plan to let the silo run completely dry and see if this fixes the problem on the successive fill. I'm a few brews into the current fill and I can already see my efficiencies starting to increase again.
I appreciate the theories though, thanks for the help!

dick-murton

Thanks for the feedback.  That suggestion really does make sense.  Never thought of that simply because we virtually always emptied silos completely before refilling - that's what can happen trying to relate large brewery conditions to small brewery conditions.  It will be good to hear what happens when you do empty completely and refill over a couple of cycles.  I really hope this is the reason - the simple ones are best.