The minimum of 8kg (17 lb) with the standard pipework - minimum batch size is 40 L (8.8 US Gal).

• We would advise against going lower than 8 kg (17 lb) of grain with the standard pipework. The overflow pipework only reaches a certain depth and the top plate is designed to fit into the overflow inlet which sits on the overflow pipework. This means the top plate only goes down as far as the overflow pipework does. As a result, with a smaller amount of grain (less than 8 kg (17 lb)) the top plate will sit a bit higher than the grain bed.
• Alternatively, you can use the micro pipework available which is explicitly designed for small grain bills. It would be best if you used the standard calculations when using this pipework.
• If you wish to do a 23 L (5 US Gal) or lower batch, we would recommend using the G30. The G70 was never designed for volumes this low (note - the first marking on the sight glass is (20 L (4.4 US Gal)).  

The maximum is 17 kg (37 lb).

• With a grain bill this size, the key is to add the grain very slowly while stirring to avoid dough balls forming. Because there is more grain, it will also take a bit longer to gelatinise.
• When pushing any brewing system to the limit there will be a small decrease in efficiency if doing this we recommend increasing your mash time, stirring the mash once or twice during the mash or by adding extra enzymes like alpha-amylase.
• Please use our brewing calculators to work this out, or the specific instructions in your manual for small grain bills.

We also have a video explaining this here.