Mash Experiments : Multi-step vs. Single Stage (Efficiency and Gravity)

A big challenge in brew in a bag is extracting satisfactory amounts sugars from the malt.

This recent experiment with mash schedules shows how temperature can have a big impact on the flavour and gravity of your beer.

brew in a bag efficiency

Although I enjoy the simplicity of brew in a bag/(BIAB), and the way it lets me test various recipe ideas easily, sometimes it’s difficult to achieve the efficiencies I’d like.

The measured gravity of the wort is always less than that predicted by recipe calculators.

In order to rectify this, I’ve been looking at how mash temperatures and schedules can be manipulated to improve brew in a bag efficiency.

This article describes two test brews and includes discoveries that you can apply to your own brewing. It’s part of an ongoing investigation into controlling and improving BIAB beers.

Using this English bitter recipe as a base, I aimed to increase the efficiency of the beer by slightly changing the variables for two different brews.

In the end I discovered much more than I expected.

What Is Efficiency And How Do You Measure It?

Efficiency is a confusing term because there are several ways to define it.

Three Types of Efficiency

In general terms, efficiency means the amount of sugars extracted from malt versus the amount available. Within this definition there are several sub-types of efficiency:

  • Dry grain fine yield
  • Brewhouse efficiency
  • Mash efficiency

Dry Grain Fine Yield

Dry grain fine yield is an absolute value that’s determined in laboratory conditions.

It represents the total number of sugars available for extracting from a given grain, and varies between varieties of malt. The value is theoretical because in practice there are many factors that affect the success of the extraction.

Mash Efficiency

Mash efficiency describes the amount of sugars extracted by mashing. Because some sugars remain in the grains, the mash efficiency is always lower than the dry grain fine yield.

Brewhouse Efficiency

Brewhouse efficiency is similar to mash efficiency, in that it takes into account the practical difficulties of extracting malt, but also factors in losses to evaporation during the boil and to the trub (hop and protein debris).

Brewhouse efficiency can be calculated if you know the dry grain fine yield of the malt and the volume of your batch, and have taken gravity readings. The easiest way to calculate is with beer software, although you can do it manually.

Click this link to see how, and for more about brewing efficiency in general.

My Typical Brew In A Bag Process

Normally BIAB brewers run a single stage mash. This means that water is heated to a set temperature and maintained at that temperature for the duration of the mash, typically 60-90 minutes.

Usually I aim one degree higher than the target temperature, because the malt cools the water when added, and apply more heat if necessary.

With the English bitter, I’ve previously aimed for a mash of 67°C and, according to the Hopville beer calculator, the best efficiency I’ve achieved is 65%.

I can do better!

Multi-Stage Mash to Increase Efficiency

A multi-stage mash involves altering the temperature of the water during the mash.

Grains are added when the water is relatively cool and left to stand before the temperature is raised. Malt responds differently at each temperature and the sugars that are extracted vary.

For this experiment, I developed a mash schedule based on recommendations by John Palmer in How to Brew (book/website):

  • 30 minutes @ 40°C
  • 30 – 70 minutes @ 60°C
  • 70 – 90 minutes @ 70°C

The first 30 minutes are to increase the hydration of the malt and encourage more enzyme activity. The second stage should produce a drier beer, which is what I want from the English bitter.

As well as changing the temperature, this also increases the overall length of the mash. If it improves efficiency, I’ll go back and investigate the influence of time in more detail.

Despite my intentions, in practice it was difficult to jump quickly between temperatures and I was forced to implement a sliding scale of heat. This is the actual mash schedule:

Mash Schedule

  • 0 – 25 minutes @ 40°C
  • 25 – 80 minutes @ 40°C – 70°C, constantly heating and hitting:
    • 50°C @ 50 minutes
    • 60°C @ 70 minutes
    • 70°C @ 80 mins
  • 80 – 90 minutes @ 70°C

The wort actually reached 73°C in the last ten minutes due to residual heat in the hob. I stirred the wort every ten minutes to keep the water at a consistent temperature throughout the brew pot.

Because of the slowness of heating, the grains were cooler overall than in either the typical single stage or the target multi-stage mash.

Comparison of Mash Schedules : Was Efficiency Increased?

Multi-stage mash gravity

Single Stage Mash (67°C)

  • Original Gravity : 1.047
  • Final Gravity : 1.022
  • Efficiency : 65%

Multi-stage Mash

  • Original Gravity : 1.040
  • Final Gravity : 1.016
  • Efficiency : 55%

Although the efficiency decreased after changing the mash schedule, the original and final gravities also went down and the resulting beer is of a similar strength.

The mash was less efficient but appears to have produced a higher proportion of fermentable sugars, leading to a drier beer with approximately the same amount of alcohol.

Ideas For Future Experiments

Despite inconclusive discoveries about efficiency, I’m encouraged after seeing that small changes to the brewing process have noticeable effects on the beer.

I hope you too can see that it’s worth testing ideas – the recipe is just the starting point. Every stage of the brew can be tweaked so you start developing custom beers yourself.

These are the things I will test next:

Increase Mash Time

Perhaps 90 minutes instead of 70 will extract more sugars from the single stage mash. If this is effective it will mean that time is an important factor, if it fails I’ll assume that temperature plays more of a role.

Add Mash Out

A mash out is where the temperature of the mash is increased at the end. The idea is that the sugars become more liquid, and are more easily released from the grains. I’ll mash for 70 minutes as normal and then increase to 78°C before removing bag.

Heat Grains With Water

I’ve also heard about a technique that involves heating the grains along with the water, before mashing for the normal temperature and time.

This is a hybrid of the the two schedules I described above, and may produce a stronger, drier beer, as it combines the features of both.

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  1. BeerKnurd

    Thanks for this great blog!

    I did 3 batches Mr. Beer, 4 Batches extract w/ grains and then have been doing BIAB for about 6 months and have done 8 or so batches using this method. I find it easy and it really works in the space I have available.

    My efficiency has been all over the map: from 53% to 83%. So, I have had difficulty getting consistent results. Even my last batch which I used a very low mash temp of 150 (and it dropped a few times as low as 146-147). I got a respectable 68.3% efficiency.

    I use an 8 gallon pot and can only fit about 6.5 gallons of water with grains in it so I am rinsing the bag with 170F water after removal and topping off the boil kettle with this rinsing water.

    Any other ideas that you have for getting more consistency from my mash?


    • John

      Thanks for commenting. Yes, BIAB is great in confined spaces!

      I’ve come to realise that a bit of variation in efficiency is to be expected, as not every beer’s the same. Having said that there are two things I think help me get the most out of the grains and, therefore, be fairly consistent:

      1. No dry patches in the mash. When adding the grains I very gently sprinkle them on the surface, waiting until each one is completely soaked before adding more. It can take a long time and a lot of patience to do this, but it ensures it’s all wet and being used.
      2. Drain well. Similar to your rinsing technique, I put the bag to drain in the fermenting bucket on top of an upturned bowl. Every few minutes I turn the grains over with a spoon, letting the wort drain down into the bucket. This happens as the main wort is coming to the boil. I’ve measured the gravity of this drained wort and it’s usually higher than the main wort, so really adds a lot in terms of extract.

      Finally, you may just need to give the mash more time.

      Sorry if this is obvious (it took me a while to realise it) but the main way to improve consistency is to pay careful attention to your process, refine it by tweaking, and then do the same thing each time you brew.

      Hope that helps. Cheers!

  2. Stuart phillips

    Got myself a brew bag and this kit

    Can I follow their instructions for the 5 litre batch and simply multiply everything by 4 for my 20 litre batch

    I guess what I’m asking is so you think the kit will work with biab



    • John

      Hi Stu,

      In terms of scaling up the recipe, it is a case of multiplying, yes. However, their instructions look to use a sieve rather than a brew bag and I think that would be difficult with a 20 litre batch. That much hot liquid is pretty unwieldy.

      I don’t see why the kit wouldn’t work with brew in a bag though as it just seems to be regular malt and hops. Do you have a brew pot big enough to do 20 litres brew in a bag? You’d need about a 30 litre pot.

      I hope that answers your question but please say if not.


  3. Stuart phillips

    My pot is indeed huge

    • John

      You should be fine then.

  4. Stuart phillips

    And thanks

  5. london

    Did you come up with the best mash temp and time. I’m guessing 67c for 90 mins.

    Thanks and Regards,