One of the aspects of heritage brewing techniques that has always raised the question of “Why?” is mash hopping.

We know that hops are used either for their oils for aroma and flavour, or for their acids for bitterness and an element of preservation, and that during the boil those oils are boiled off.

There’s first wort hopping, where hops are added to the copper as the wort is transferred in from the mash tun, this gives the longest time for the acids to soak out of the leaves without extending the boil length.

Then there’s early hop additions, the bittering additions. These are usually added as the wort comes to the boil, and usually mean that they have about sixty minutes of boiling to get out a lot of the acids for bitterness.

There’s also mid-boil flavour additions. You get some bitterness from these, but generally these hops are more about the flavour than any real bitterness.
And there’s late hop additions, usually added with tend minutes left of the boil and to give the beer a hoppy aroma.

Once the wort is in the fermenter, you can add hops with the yeast for a bio-transformation hop addition so that the heat generated by the initial exothermic stage of fermentation draws out more of the hop oils that little bit quicker, along with some extra flavour elements from the vegetal matter of the hops.

And then there’s dry hopping, where you add hops once fermentation has finished so that the oils soak in gently and don’t have time to then fade away, giving you the most aromatic use of hops.

And this is all that brewers have really used hops for in recent years.

When you add hops to the mash, you don’t get any additional bitterness from them, in fact in theory it’d be less than you’d get adding them to the copper. And you certainly don’t get any aroma from them, because any oils that seep out will be either soaked up by the grain, or boiled off in the copper. The only two reasons that could be thought of for using hops in the mash is if your copper didn’t have enough space for the wort and the amount of hops you needed – which was unlikely, or if you wanted to get an extra, more rounded hop flavour – which it does bring.

But we’re only looking at the hops here, rather than looking at the overall processes going on in the mash tun. When we add hot water to the grain, the amylolytic enzymes on the malt start to convert the starches to sugars, which the yeast will later convert to alcohol and carbon dioxide. Modern malting and kilning techniques have led to us having good, efficient malts with a high level of enzymes on them, meaning we get a lot of conversion. But historically this wasn’t the case. The malts themselves weren’t as good (although they arguably had better flavours) and the enzyme content was a lot lower than it is now. As an example, a standard pale ale malt has an efficiency of about 82%, and a heritage grain kilned to a modern pattern has an efficiency of about 72%. When we had some of that same heritage grain kilned to a historic pattern the efficiency came in at closer to 65%. When we added some German Pilsner malt which is known for having a high enzyme content, we saw the overall efficiency rise to 75%. 

Which brings us back to mash hopping, it’s known that the more enzymes in the mash, the better the conversion. As I point out in this article: there was another use for hops that until recently was seen as a Very Bad Thing, although some brewers are starting to come around to it having practical uses. Hops contain the same amylolytic enzymes as malt and this can lead to problems in packaged beer – especially cans of highly dry hopped IPAs – with an ongoing fermentation, an increase in pressure, and an explosion. But this hop creep was used historically as a way to deliberately keep that fermentation going in casks so that the beer was sparkling and fresh when it got to its destination.

So here’s the theory that now needs testing:

Mash hopping was nothing to do with adding bitterness or aroma to the final beer, but was instead a method of increasing the enzyme content of the mash tun (along with dropping the overall pH of the mash) to improve mash efficiency. 

Mash hopping had nothing to do with using hops for bitterness or aroma, but rather for the third, much less recognised use for hops, their enzymatic content.