Ask The Experts: Mash Efficiency

We often get questions sent to us from home brewers who need a bit of a steer in the right direction, so we decided it would be a good idea to add our answers to the blog to share the knowledge with everyone! Feel free to email us if you have a brewing question.


I’m a few batches into the BIAB method and my efficiency is terrible. I’m scratching my head a bit and just trying to eliminate possible causes. Any ideas?


Hi James,

Poor efficiency can be caused by a few factors. One of which is too coarse of a crush. This can be a bit of a juggling act as too fine a crush can end up with a stuck sparge (when the mash won’t drain). We use a 3 roller mill which generally gets a very consistent crush which suits most brewers. If you want it a little bit finer, ask us to “double mill” and we’ll put it through the mill twice for a bit more crush which works well for BIAB.

Some other efficiency tips:

  • Try a longer mash, 90 minutes (as opposed to 1 hour) works well.
  • Try doing a “mash out”, raising the temperature of the mash to about 76-78c at the end of the normal mash schedule, prior to removing the grain.
  • Mini “sparge” – a sparge is not normally associated with BIAB, the process is basically rinsing the grains of trapped sugar with some extra water. To do this, transfer the grain bag to a food-safe bucket or pot and add a few litres of mash temp hot water back over the grain to rinse out more remaining sugar, you can then add that liquid back to the boil kettle.
  • You may wish to squeeze the grain bag a little to get out extra absorbed liquid and sugars. Some people will tell you this will extract tannins and make the beer astringent. Those people are wrong. If you don’t believe us do a google search for “HEBS – High Efficiency Brewing System”.

Of those suggestions, we highly recommend as a start try a 90 minute mash and mash out temperature, as they do raise efficiency without any substantial extra mess or work.

Cheers, Sam.