It’s rare that a given home brew recipe matches your brewing efficiency, hop variety or target batch size. Use these calculations to resize any recipe on brew day.

When planning a brew day, home brew recipe conversion is my first task. Usually I do these three things:

- Resize quantities
- Adjust for efficiency
- Adjust for hop alpha acid percentage

In this article I explain how to do each of them with an example recipe, taken from the International Homebrew Project.

The original recipe for a 23 litre batch asked for:

Malt

12 kg pale ale malt (70% efficiency)

Hops

East Kent Goldings (4.5%) 152g for 90 minutes

Fuggles (5.5%) 85g for 20 minutes

Fuggles (5.5%) 35g dry hopped

### Resizing The Recipe

This is the most straightforward set of calculations. Quantities convert proportionally according to this equation:

Because the example recipe has an especially large grain bill, I want to brew just 10 litres.

Using the above formula I can scale the recipe quantities down:

Malt:

Hops Kent Goldings 90 minutes:

Hops Fuggles 20 minutes:

Hops Fuggles dry:

This would be my recipe if everything else in my brew set-up matched that of the recipe author. That is rarely the case.

(To convert between metric and imperial units check here).

### Adjusting Efficiency

The next task is to change the malt quantity to match the efficiency of your brewing equipment. If you are in the habit of taking gravity readings each time you brew, you’ll already have an idea of your efficiency.

I won’t go into detail here, but basically efficiency describes the amount of sugar you extract during the mash versus the maximum available for extraction. It’s expressed as a percentage.

Inputting gravity readings into brew recipe calculators such as Hopville tells you your efficiency for a particular brew. In general each brewer is fairly consistent because efficiency is mainly determined by brewing method and equipment.

At the time of this brew I was averaging 60% efficiency so adjusted the malt quantities accordingly. If you don’t do these adjustments, the beer will turn out weaker than you expect (or stronger).

The efficiency adjustment formula is:

In my example (using the scaled down quantities) this looks like this:

I now know how much malt I need to achieve the original gravity of the recipe with my batch size and efficiency.

### Adjusting Hops

The last thing to convert are the hop additions.

As you may know, hops add bitterness to beer. The amount contributed depends on the percentage of alpha acids in the variety used.

When you buy hops they include information about the alpha acids in the form of a percentage. Similarly, recipes state the alpha acids percentage assumed when determining bitterness levels.

Often, hops you buy differ from the recipe assumption and you need to perform another brewing conversion:

I’m using 5.3% Kent Goldings and 4.8% Fuggles. These don’t match the recipe hops, so I use the formula to find out how many to use:

Kent Goldings:

Fuggles:

Fuggles Dry:

Use the hop weight for your batch size, not the amount of the original recipe.

Remember that if your hops have more alpha acids you use less of them, and vice versa.

### Converted Recipe

My new 10 litre recipe adjusted for my hops and efficiency is:

Malt

6 kg pale ale malt (60% efficiency)

Hops

East Kent Goldings (5.3%) 56g for 90 minutes

Fuggles (4.8%) 42g for 20 minutes

Fuggles (4.8%) 15g dry hopped

Now get on and brew.

## Comments...

I’m curious to know what volume of water you started off with? I’m learning to adjust, I as I only have a 10 litre Cool Box and I also have to adjust for boil off so I’m not left with 3 litres of wort!

Hi Stuart,

With this particular batch I started with 19 litres and bottled around 9. The losses were pretty big because of the large grain bill.

There’s a bit of trial and error at the beginning to find out what the losses are on your system – it’s different for everyone.

It’s really surprising how much water is lost, especially during the boil. I also find that as a percentage the losses are greater with smaller batch sizes.

I don’t know what you’re aiming for, but starting with 10 litres I’d expect (on my brew in a bag set-up at least) to get around 5/6 litres of beer. If you’re doing full all grain, with sparging, that will give you more.

If you find you’re not getting as much as you want, you could always prepare some water in advance for topping up the wort just before pitching the yeast. You’d just have to keep an eye on the gravity points to make sure the beer doesn’t end up too watery.

Hope that helps. Cheers!

Ah ha! John, that link to the open source brewing software may just be the solution to all my brewing problems!

This chap http://www.mashspargeboil.com/complete-guide-to-all-grain-brewing/

seems to come up with some ideas, such as doing two mashes, which will hopefully allow me to do two 10 litre mashes and allow me to finish with at least 10 litres of wort.

Many thanks for taking the time to reply and helping me out,

Regards,

Stuart

No problem, glad to help.

Mash Sparge Boil is a great brewing resource, so I’m sure those ideas will work well.

Good luck!

How do you scale up?

Thanks

It’s the same process. What do you want to do exactly?

Looking at scaling from 20l to 1200l

Cheers

The same equations should work, although that’s far more than I’ve ever brewed in one go.

If you have a specific recipe in mind I could show you how to get started.