Why Your Wort Has A Low Original Gravity & How To Fix It


picture of a hydrometer

Recently I moved house and had to also change some of my brewing equipment along the way.

When I brewed my latest batch using my new (old) set up, I noticed that my wort’s Original Gravity (OG) was way off what it should have been.

So, being a humble homebrewer, I decided to go back to basics and hunt out the reason for this.

A lower Orignal Gravity than anticipated is due to inefficiency in the brewing process. This can be from miscalculations in the recipe, ingredients used, as well as poor mashing and sparging techniques. Often, there is just a misunderstanding as the recipe doesn’t match the brewing equipment, so the OG is actually correct.

There is no one answer to why you may be missing your OG, so if you are struggling with the same thing, read on until you get that ‘ah-ha!’ moment

How to fix wort with a low original gravity right now

Right, first thing is first.

You are probably reading this because you are standing with your phone in one hand, a hydrometer in the other, staring down into a disappointingly sugar-free wort.

Well, perhaps not totally sugar free.

So, before we figure out WHY this happens, let’s talk about how you can fix a low original gravity in your wort before you lose too much daylight.

Luckily, fixing wort that hasn’t had ‘enough’ sugar released into it is relatively easy. All you have to do is to add more fermentable sugars which your yeast can use later on during your pitching phase.

A great source of fermentable sugar, which you may have lying around, is Dry Malt Extract (DME). Alternatively, if you don’t have any or can’t get to your local home brewing supply store, you can use regular sugar.

How to raise your OG using DME

What you need to do is to measure the difference between your estimated OG and your actual OG. You then multiply that difference by 1000 and this will give you the ‘points’ you need to raise your wort’s specific gravity by.

For example, if your target OG is 1.065 and your actual OG is 1.042 you need to change the density by 23 points ( 1.065 – 1.042 x 1000 = 23).

This means that you need to add a quantity of DME which is equivalent to 23 points per gallon of DME. Right, are you confused because I was?

What this means is that we need to know more about DME and how it relates to Specific Gravity.

So, DME has a potential of 1.046 and will add 46 points for every pound of DME added to your wort. So, in our case we only need 23 points, so divide 23 by 46 and you get 0.5 or half a pound of DME.

Of course, if you are brewing more than a gallon of future beer, you need to adjust those sums accordingly.

Using regular sugar will work in the same way.

Disclaimer: The above fix is only really valid assuming that everything else in your process is accurate. What I mean to say is, did you really miss your OG, or does it just appear that way because of other factors.

If you really want to know why you have missed your target OG, and perhaps are doing it consistently, you need to check a few things with your brewing system and brew day.

What causes low original gravity in homebrewing?

Hitting your intended Original Gravity may seem a doddle to a seasoned (or is that sessioned?) homebrewer, but it actually involves a lot of things going right.

A lower pre-boil original gravity than expected is often due to inefficiency with the extraction of fermentable sugar from the mashing or sparging processes. This can often happen due to a lower brewhouse efficiency than realized or because the brewer is using an incorrect grain bill for their system.

Again, there are quite a few things to think about here, so make sure you read on to check what you are and aren’t doing efficiency on your brew day.

An issue with your grain bill

As I’m sure you know, your OG is connected to the amount of fermentable sugars that are floating around your wort in the brew kettle in front of you.

If it appears that you have less sugar than needed, the obvious first step is to go back to the source, the grains you are using.

Crush of your grains

In order to work at the height of efficiency, you need to ensure that your grains are being crushed properly.

According to many expert homebrewers, such as Brad Smith from Beersmith, you need to ensure that your grains are being pulverized internally why not being overly deformed externally.

This can only be achieved with the right type of grain mill, something like the Barley Crusher (check out the listing on Amazon) which has the ability to achieve this perfect crush where other grain mills might fall short.

If you don’t crush your own grains but buy them pre-crushed from your local homebrew supply store, then chances are they are being crushed properly.

I say this only because homebrewers as a group are very discerning consumers and an LHBS clerk who wasn’t providing the right crush wouldn’t be doing it for long!

There is another issue with your grain bill which might be relevant to you, but I’ll go into that a little bit later in this article.

The inaccuracy of measuring equiment

I have to admit that I fall into the group of people who just expect things to work. What I mean is, if you have a piece of measuring equipment I used to asume that it would indicate the correct measurment from the get-go.

That was before I started brewing my own beer, that is.

Are you using your hydrometer correctly?

If you are early into your career as a homebrewer, it’s important to know that your hydrometer, a key bit of kit when it comes to measuring specific gravity, lies to you.

The first thing to know is that when you are reading your hydrometer, it may not give you the exact measurement as it appears to the eye.

Basically, due to the refraction of light, the natural bubble (meniscus) which forms where the hydrometer meets the surface of the wort will give you a false reading.

Always read your OG from the line that appears at the bottom of the bubble, not the top.

However, this would only give you a difference of about 0.002, or two points which isn’t much.

But the hydrometer has other lies it tells!

The affect of temperature on hydrometer readings

Before you dump a lot of DME into your wort, take a moment and think whether or not you calculated for the hotter temperature of your wort when you took your reading.

Hydrometers are pretty low tech, even if they are very useful to the homebrewer, so you need to work within the parameters that they were designed for.

Chances are that your hydrometer is calibrated at 60 °F (15.6 °C). However, some models are calibrated at other temperatures from 58 °F (14.4 °C) to 70 °F (21.1 °C).

Warmer temperatures can REDUCE your OG by half a point (0.0005) whereas going the other way and reading it at 5 °F too cool, you’ll get an increase of about a quarter of a point (0.00025).

So, using a hydrometer temperature calculator may instantly solve your current headache.

Making sure the recipe fits your ingredients

It’s pretty normal for a newer homebrewer to follow a recipe they found online or in a book.

Personally, I love working out of books like ‘The Joy of Homebrewing‘ and seeing if I can replicate Charlie Papazian’s creations. (I got my copy from Amazon).

The issue there, and with every single recipe you find anywhere, is that you can’t blindly follow it.

It’s important to sit down and do your own calculations on whatever brewing software you prefer to make sure that your ingredients (grist, water, and so on) fit your own personal set up.

A number on the page may be completely unobtainable by you today following the recipe created by another brewer using totally different equipment.

So, what I’m saying is that the ‘missed’ OG you think you have might be the ‘perfect’ OG for the beer you are ACTUALLY brewing.

Basically, check your recipe because the issue may be there.

Lower brewhouse efficiency that you thought

Above we spoke about an OG which was lower than predicted because it wasn’t accurately calculated for the ingredients being used. But there’s another issue to consider, which is quite common. Brewhouse efficiency.

What is brewhouse efficiency?

Your brewhouse efficiency tells you the potential your brewing setup has to extract fermentable sugars from grains into your wort.

It’s expressed as a percentage and takes into account the loss your personal brewing system will ALWAYS have due to a number of factors.

When you want to get serious about homebrewing and to become more consistent with your brews, knowing this number is important.

A fairly typical estimation of the average homebrewing system is around 70% efficiency, but you could be way below that. You can calculate it by using a brewhouse efficiency calculator.

For our topic, knowing this number may be the solution to a consistently low original gravity. If you are following a recipe that assumes a brewhouse efficiency of 70% but you are actually nearer 60% or even 50%, it just won’t give you the final numbers you are expecting.

In this case, you don’t need to give up and go home ( wait, you are probably already at home), you just need to adjust your recipe and add more base malts to make up the difference.

In fact, my professional brewing friend Tom always says, just add more every time because it’s easier to dilute a beer than add more sugars later.

What leads to lower brewhouse efficiency?

One of the main causes of a lower brehouse efficiency is to do with dead spaces in your mash tun.

If the grains get stuck in a corner or under some tubing, they will keep the sugars locked inside them when you are sparging. The same goes for any space that is below the level of your faucet when you are draining your wort.

By simply opting for a cylindrical rather than a flat bottomed mash tun, you could see your efficiency go up.

Check out some mash tuns you can get from Amazon which may help solve this issue.

Igloo 5 Gallon Portable Sports Cooler Water

Although sold as a cold beverage cooler, this works great as a mash tun. Check out the deals on Amazon

Igloo 4101 – 10 gallons

If you are planning to brew larger batches or need more strike water, then the 4101 might be a better fit. Again, you can pick this cooler up on Amazon today.

Mash Tun False bottom

If you are going down the DIY mash tun route, make sure you get yourself a false bottom as this will help with your brewhouse efficiency. You can pick up a fairly inexpensive model on Amazon these days.

Inefficient mashing techniques

If you’ve gone through the list above and determined that nothing seems to fit the issue you are having, then likely it’s a problem with the mashing process itself.

When mashing in it’s very important to give your grains a really good stir, for up to 5 minutes to really make sure that they are properly mixed in with the water.

Remember that you extract most of your fermentable sugars within the first 20 minutes or so of your mash, so it’s important to get this step right.

Other concerns should be getting the right ratio of water to grain and knowing your grain absorption rate. You can calculate both these things in your brewhouse software and by keeping good brewing notes.

In addition to this, you want to keep a close eye on the mash temperature, ensuring that you don’t overcook the mash if using a naked flame.

It’s important to keep the enzymes within the grains happy, so don’t go over 75°F while mashing. The higher the mash temperature the longer the sugar molecules and the harder it will be for your yeast to break them down later.

Sparge correctly

Finally, if you can be sure that none of the issues we’ve discussed so far is the culprit to the low OG you are getting, it must be due to inefficient sparging.

If you aren’t totally familiar with all the different sparging techniques, you can read about them in my other article here.

With almost all of the sparging techniques, with perhaps the exception of the no sparge method, these two things will lead to a better extaction of fermentable sugars into your wort.

Sparge hot

Using hotter water than your mash temperature, say around 70-75°F, will help your sugars flow better.

The warmer temperature just makes everything more viscous and will lead to more sugar being ‘washed’ out of the grains as you sparge.

Sparge slow

Don’t rush your sparge. The sparge water really does need time to perculate down through the grains and grain bed, so don’t let it escape your mash tun at much more than a trickle.

Any quicker and you’re likely to be leaving a lot more fermentable sugar behind than you should be.

Phil - BeerCreation

Hey, I'm Phil. I'm passionate about all things beer. I love making it, drinking it and best all, learning about it!

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