In the most recent batch, I achieved a much lower extract efficiency than I was expecting, and measurement of the first runnings gravity indicates that the vast majority of the loss can be attributed to the sparging process. I have a suspicion that the problem is in part due to sparge water channeling around the outside of my vegetable steamer false bottom. The ‘petals’ don’t have enough weight to stay tight against the outside of the lauter tun, and some tend to spring back a few millimeters. The weight of the grain bed ought to hold them tight against the sides, but even then there are decent sized gaps.
To remedy this, I had an idea: why not cut some plastic tubing lengthwise, so that it has a ‘c’ shaped cross-section, and wrap it around the outside to form a seal with the sides of the lauter tun. We’ll see if lauter efficiency is any better in batch number three.