Colin Kaminski and I have just had a discussion regarding kettle wort pH and we agree that hop forward beers need a wort pH of 5.4 in order to accentuate the hopping. A low wort pH will reduce the hop expression.
It is true that higher kettle pH leads to increased ionization and therefore more solubility of hops alpha acids and therefore, presumably, more isomerization but it should be pointed out that there are advantages to lower kettle pH such as improved brightness of the runoff, better break formation and less demand for acid production on the part of the yeast as they are going to strive to get wort pH where they want it irrespective of what you give them. pH 5.4 is probably OK for kettle pH but is at the high end of the recommended range. I don't recall exact numbers but it seems to me that most texts want you in the 5.0 to 5.2 or perhaps 5.2 - 5.3 range. Now all this, including what follows may be interesting but moot because I and the texts are all talking about pH at the conclusion of the boil, and Martin and Colin may be talking about the onset. Some breweries add salts and/or acids to the kettle but the usual goal is reduction of pH.
I thought it might be interesting to try to WAG what the effects of an increase in wort pH might actually have on bitterness. The graph below shows what I came up with. The horizontal axis shows hypothesized fractions of the alpha acid that are ionized at some normal but unspecified pH. The left vertical axis shows the fraction that is ionized if the pH is increased above the normal pH by 0.1, 0.2 or 0.3 pH and the axis on the right the percentage increase of ionized acid for those same pH increases. For example, assuming that one normally gets 20% ionization, increasing pH by 0.3 would increase that to 33% which represents a 65% increase in the concentration of ionized acid in the wort.
It is also worthy of noting that if you want knockout pH as high as 5.4 you are probably going to have to add alkali to the kettle as there is naturally an appreciable drop there. Looking back over my logs it seems to average 0.3 pH with respect to the initial mash pH. As mash pH generally drifts up a bit as the process proceeds the drop in the kettle is probably a bit more that that with respect to lauter pH. Bear in mind, of course, that my logs represent my brewing, not the universe of brewing and other people brewing different beers in different ways may have appreciably different experience.
Do stay away from chloride content higher than around 50 ppm if you are boosting the sulfate over 100 ppm.
I think better advice here is to start with low levels of chloride and sulfate and then experiment in tasting to see what levels prove desirable. Individual taste very much comes into this.
The chloride is wasted since you are trying to produce a dryer or more bitter focus in the beer.
The man has not expressed a preference for dry bitter beer. He is specifically asking how to avoid that excess bitterness which is so popular in craft beers today. And he might not want dry beer either.
There are two types of dryness to consider. There is the dry bitterness of the hops which I call harshness though I see why people might call it dry and then there is the dryness that comes from a highly attenuated wort. The two are independent. In the beers I brew (continental lagers for the most part) I avoid the former by shunning sulfate and using noble hops and get the latter by saccharifying below 150 °F.
Finally I think it worth noting that if I want a bit more bitterness I just add hops. Colin Kaminski is is a very different position. He has to make a profit. I don't. He needs to squeeze every BU and every °P out of his raw materials.
