We are regularly contacted by customers who have had a poor yield and wonder what the cause is. Let's take a look at what can affect this, and how we can optimise efficiency.
When we talk about efficiency and yield in beer brewing, we are talking about either mash efficiency or brewhouse efficiency. In this article we will focus on mash efficiency.
If you are unsure what these terms mean, we have written a separate article that we recommend starting with: «Mash efficiency vs brewhouse efficiency».
Why is my yield too low (OG too low)?
For the average homebrewer, it is usually mash efficiency that causes problems, i.e. how close you get to the OG (original gravity). You should not get too hung up on mash efficiency if you land a couple of points below or above the expected OG. If, on the other hand, the deviation is larger, there are several factors you can look at more closely to get a better yield.
You may not find the exact answer to your particular problem, but by going through the typical causes of poor yield you have a good starting point for troubleshooting.
Malt and milling
Sometimes the brew shop's standard malt crush may not be optimal for the equipment you brew on. The crush you need depends on the equipment you have. If you brew with the BIAB method, for example, you will often want a somewhat finer crush, while a brewing machine from Speidel benefits from considerably coarser malt.
In a perfectly crushed batch, about 20% of the grains should look as if the husk is intact, even though it is cracked/opened. When you squeeze the malt that looks uncrushed, you should hopefully notice that the husk opens easily.
This is what a perfect batch should look like:
- 10–20% “flour”
- 30% fine grits
- 30–40% coarse grits
- 20% grains with the husk partly intact
To have full control of the crush, we very strongly recommend investing in your own malt mill. Then there will be no variation in the crush, since you can adjust the mill yourself. You get the malt crushed exactly the way you want, and you are guaranteed fresh, freshly crushed malt on the brew day itself.
In our Malt mills category you will find both manual malt mills, where you can attach a drill or turn the handle yourself, and fully electric ones such as this malt mill from Grainfather.
Mashing in
Mashing in is when the malt is stirred into the water, and good routines here can affect your yield. The key here is to take your time.
If you add all the malt at once, you risk parts of the malt not coming into proper contact with the water. Lumps of dry malt (dough balls) form, and malt that does not come into contact with water will have no effect. It can also lead to “channels” in the grain bed during sparging, so that you do not get all the sugar out.
We recommend adding the malt a little at a time and stirring well in between. Feel free to use the mash paddle to cut through the grain bed as well, to further reduce the chance of lumps.
The mash
Again, the key word is time. Even if the recipe says to mash for 60 minutes, it is no problem to leave it considerably longer. Then you can be completely sure that all conversion processes are complete, especially if you are brewing with a lot of malt. Some brewers even mash in in the evening and leave it until the next morning before the boil.
As a rule, you should not stir vigorously during the mash after mashing in, but some brewing machines, especially those with tall and narrow malt pipes, can benefit from a couple of gentle stirs along the way to avoid “channels”. This applies especially if you were not careful enough when mashing in.
Mash-out
Towards the end of the mash it can also be a good idea to do a mash-out. A mash-out means raising the temperature of the mash to the same temperature as the sparge water.
This process stops the enzymes that convert starch to sugar and “locks” your sugar profile. The temperature also keeps the sugars you want in the wort more fluid, making them easier to extract.
Amount of malt
Most brewing machines state a maximum amount of malt. Even though it is possible to fill up with the stated amount, or perhaps even more, it is not always a good idea. Because of the large amount of malt, the grain bed becomes very compact, and you risk poor circulation during the mash and/or not being able to sparge properly afterwards.
Some brewing machines have tall and narrow malt pipes, and these quickly become too full to give a good yield. If you are going to brew a strong beer, it may be an idea to double mash (split the malt in two and mash in two rounds), reduce the amount of malt and add spray malt, or brew a smaller volume at a time.
Amount of water
If you mash in with too little water, you can quickly run into yield problems. Even if the recipe states an amount of water, you should not always follow it slavishly. Instead, use a little more mash water and reduce the amount of sparge water.
As long as you have the right volume before the boil, there is no fixed rule for how much water goes into the mash or the sparge. The mash should have roughly the same consistency as slightly thin porridge.
Sparging
This is often where many people lose a lot of efficiency. As we have already mentioned several times, the key is time. What many people do wrong is to pull up the malt pipe and sparge quickly straight away. The problem with this is that the water will not carry with it all the sugar you want in the boil, because the sparge water runs through far too quickly.
This is how we recommend sparging:
- Lift the malt pipe and let it drain well and for a long time, ideally until it has almost stopped dripping. This helps any channels in the grain bed collapse, and you avoid the sparge water being “sucked” through them without taking the sugar with it.
- Sparge with hot water (75–78°C), a little at a time. Feel free to use a measuring jug or similar so that you spread the water well over the grain bed. There should be no more than a couple of cm of water above the malt at most. Take your time and let the sparge water run through well before adding more.
- Repeat until all the sparge water has been used, and leave it alone until it has almost stopped dripping. Do not squeeze the malt unnecessarily, as you can easily get tannins (astringent off-flavours) in the wort. The same off-flavours appear if you sparge with water that is too hot.
pH and water chemistry
Generally, this is not where a new homebrewer should start troubleshooting, but it is worth keeping in mind. The pH of the mash can affect the enzymes that convert starch to sugar. If you learn a little about simple water adjustment, this can be the key to getting the last missing points. You can read more about this in the article «Water adjustment when brewing beer»
Malt can vary
Grain is a natural material that will never be completely identical every time, even though in principle it should be. Even the largest maltsters can never avoid variation in the amount of starch from batch to batch.
You also have to allow for the fact that the figures in pre-programmed recipes (when brewing recipes with Brewfather or similar) are not necessarily entirely correct or up to date. It is possible to find the manufacturer's figures and calculate very specific numbers, but here we are really talking about nitpicking that will not be the biggest contributor to the right yield.
How to fix a poor yield
Have you brewed and the “damage” has already been done? There are still a couple of things you can do to correct the problem straight away.
The best time to check this is after sparging and before the boil. Stir the wort well before taking a reading, so that any sugar that may have settled on the bottom mixes well with the rest. Take a sample and take a reading with a hydrometer, refractometer or similar. This figure is called the pre-boil gravity or SG (specific gravity). The recommended temperature for reading the correct value with a standard hydrometer is 20°C, and 10–30°C for a refractometer with ATC (automatic temperature compensation).
If you are a couple of points below the expected pre-boil gravity, it is nothing to worry about, but if the deviation is larger, there are some quick fixes we can turn to.
Spray malt and malt extract
It is always wise to keep a bag or two of spray malt (DME/dry malt extract) or malt extract (LME/liquid malt extract) in reserve. If you are unlucky and get a poor yield, you can add a little of this to hit the right numbers.
Spray malt and malt extract should be boiled for 10–15 minutes so that it dissolves properly and is sanitised. It is therefore sensible to find this out before starting the boil by measuring the SG/pre-boil gravity.
How much you need to add varies with the volume of wort and how far off you are. You can calculate this in, for example, Brewfather's Gravity Correction or with a calculator such as this one from Brewers Friend.
Extend the boil time
If you have neither malt extract nor spray malt to hand, it is still possible to make adjustments. This is also a good method if you are only a few points below the expected SG. Here it is quite simply a matter of extending the boil time. That means boiling the wort for a period before starting the normal boil time. This reduces the water and concentrates your wort.
This means that brewhouse efficiency is somewhat reduced, but you get closer to your actual OG. So the choice is yours: do you want the planned volume, but a weaker beer? Or do you want a smaller volume of beer with the right alcohol content?
It is also worth bearing in mind that less wort will also affect the bitterness. If you choose to reduce the volume of wort, it can be wise to reduce the amount of bittering hops to balance your brew. It can also be wise to hold back other hop additions until you start the actual boil time.
How much you may need to boil off can be found in the same calculators from Brewfather and Brewers Friend. These calculators can also be used if your OG is too high and you need to dilute your wort to the right volume.
