Lesson 4 - Wort Boiling Technology and Process Control

The following wort boiling systems have been used experimentally and, in some cases, marketed but may not currently be used to produce beer commercially.

Microwave wort boiling

If you have a microwave, you know that microwaves can heat liquids. They work by making polarised molecules like water vibrate.

Microwave wort boiling is done in a conventional kettle. The microwave generator, and its associated electronics, are located outside the kettle in a control cubicle. It requires about 60 kW of electrical energy (depending on kettle size) and a cold water supply for cooling. The microwaves travel to the kettle via a wave guide, passing directly into the wort. The beers produced experimentally using the system were found to have poor flavour stability.

Wort boiling with gas sparging (also known as simmer and strip)

Although grouped with some of the more obscure methods, gas sparging is currently in use in a number of large breweries and one multinational brewer uses it globally. Gas sparging involves passing small bubbles of CO₂ or nitrogen through wort heated to just below boiling point. The gas bubbles do jobs that the steam bubbles do in conventional boiling like, mixing the wort, stripping volatile compounds and providing an interface for trub formation. The total evaporation can be as low as one percent, resulting in the potential for significant energy savings (an 80% reduction is claimed by the multinational brewer who uses this method).

Another option is to sparge a kettle that is boiling with gas. When this is done, evaporation rates can be doubled resulting in reduced boil times and energy usage. Gas sparging can be used to remove worty aldehydes when producing no and low alcohol beers.

PDX wort boiling system

The PDX wort boiling system injects clean steam at high velocity (about 1000 m/s), into reactor chambers through annular nozzles. The high velocity causes a drop in pressure inside the reactor chamber causing the wort to form vapour and tiny droplets of liquid. Wort leaves the reaction chamber in a two-phase flow which is returned to the kettle. A number of benefits are claimed for the PDX. These include:

• Up to 50% reduction in steam requirement
• Less frequent CIPs

The PDX was trialled extensively when it was launched and most of the breweries that trialled it rejected it due to a burnt off-flavour. It may still be in use in some breweries, but the supplier is no longer trading.

The subject of energy saving has come up throughout this lesson and in the next few sections we will discuss the ways in which this can be achieved.