What is Beta Glucan

What is beta glucan

Having trouble with slow wort run-off? This molecule may well be the cause of your problems.

What are Beta Glucans?

Any home brewer that has had a stuck mash, that is a mash that runs off very slowly or not at all, will have encountered this interesting but incredibly frustrating polymer.

Glucan is a term that encompasses all polymers of glucose. Therefore starch is a glucan but it is a very different molecule to beta glucan and this is all down to how it is constructed.

But what is beta glucan?

Beta glucan is a glucose polymer typically found in the endosperm of barley and also malt. In particular beta glucan is a structural component of the cell walls in barley and malt.  The interesting aspect of beta glucan is that as a polymer of glucose it is very similar to starch.  However, the glucose molecules in beta glucan and starch are linked together in a very different way and that is what gives beta glucan very different functional properties compared to starch.

Whereas starch is an alpha linked glucose polymer, beta glucan is, as the names suggests, a beta linked glucose polymer. This structural difference is very important as it provides the brewer with a unique set of challenges if the beta glucan is not degraded sufficiently during malting.

During malting the cell walls and in particular the beta glucan components of cell walls are broken down. This is an essential part of the malting process as the cell walls need to be broken down to liberate the starch granules hiding within the cells of the endosperm.  If the cell walls are not broken down we can’t extract the starch during mashing and convert it into fermentable sugars.  In essence we won’t be able to brew beer.  However, as with all good things and brewing beer is a good thing, there is a minor downside.  The downside is that, although we have liberated those starch granules, we have also, by breaking down the beta glucans, increased significantly the solubility of the beta glucan.  By increasing the solubility we are allowing them to be extracted during mashing.  But what is the problem with that I hear you say?  Well the main problem associated with soluble beta glucan is that it greatly increases the mash and wort viscosity slowing up wort run-off and in extreme cases completely stopping it.  So if you have ever experienced a slow run-off from your mash tun then it is highly likely that the malt that you are using has a high beta glucan concentration.

Should you as a home brewer expect to have a beta glucan problem?

In essence if the maltster has done their job properly you should never have a problem with beta glucan impeding your wort run-off. Most of the beta glucan breakdown occurs during malting and is done by a group of enzymes that are rather creatively known as the beta glucanases.  This is a group of enzymes which, as long as the malting conditions are right, will more than adequately break down beta glucans.  The enzymes themselves are very heat sensitive and are denatured at temperatures much above 55°C.  Therefore most of the beta glucanase activity is lost during kilning meaning that there is not much left in the finished malt.  Furthermore if you mash in at standard infusion temperatures of around 65°C then any beta glucanase activity left in the malt is rapidly lost.

Therefore how can you ensure that you will not experience a run-off issue due to beta glucans during mashing? The easiest way is to check your malt analysis certificate.  If you haven’t got one then ask your home brew shop for one every time you buy your malt.  Check the certificate carefully and where it says beta glucans make sure that the level in malt is as low as possible.  In terms of numbers anything below 100 mg/l should give you no problems at all.  Between 100 – 150 mg/l should also be fine but you might encounter a slower run-off.  Much above 150 mg/l is not ideal and the malt is probably best left sitting in the homebrew store.  Apart from anything else a high beta glucan level in malt is an indicator that the malting process has not been as effective as it could have been and that the malt is poorly modified which can give rise to other brewing problems.

Can you brew with malt which has a high beta glucan level?

If you brew using a single temperature infusion mash, where you mash in above 60°C, then the answer is it will be very difficult to brew with malt with a high beta glucan level. This is because the beta glucanases, the enzymes responsible for breaking down beta glucans, are rapidly de-activated at these higher temperatures.  There is therefore going to be limited enzyme activity during mashing.  You can mash in at a lower temperature if you know you have malt with a high beta glucan level.  This can be combined with continental style protein stand at 45°C.  Or if your mash tun is capable of doing it mash in at 45°C for protein breakdown and then heat to 50°C – 55°C to breakdown beta glucans before heating up to 65°C for the saccharification rest.


  1. Partha Mehendale September 19, 2016
    • Dee Kupa February 27, 2017

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