Ask Mr. Wizard

Brew-In-A-Bag Water Chemistry


Dave Allen, Indianapolis, Indiana asks,

I recently switched to 10-gallon (38-l), electric brew-in-a-bag (BIAB) batches, from 10-gallon (38-l), three-vessel batches, and my beer quality has dropped to a depressing level. The first brew was a lightweight Hoppy beer that came out very flabby. No real personality, just sort of blah. The next was a darker beer with lots of flaked oats in the grist. It did not attenuate and is so worty as to be undrinkable. These batches have me questioning the mash chemistry as it relates to such a loose mix. I am using full PRE-boil volumes to mash, then draining the basket and putting the heat to it. With about 20 pounds (9.1 kg) of grain and 17 gallons (64 l) of water, am I diluting the mash so much as to make a water adjustment (or PH adjustment) necessary?


The first thing I do when discussing mash thickness is to calculate the liquor-to-grist ratio (water weight divided by grain weight) because this ratio is the basis for discussion related to thickness. Infusion mashes typically range from 2.5–3.0 L/kg (1.2–1.5 qts./lb.) and stirred mashes usually range from 3.0–5.0 L/kg (1.5–2.4 qts./lb.), with 5.0 L/kg (2.4 qts./lb.) being a very thin mash. Your mash has a liquor-to-grist ratio of 7.1 L/kg (3.4 qts./lb.), which is extremely thin. So what is the significance of mash thickness?

In the view of many brewers, mash thickness mainly relates to functionality. If you are doing a single-temperature, infusion mash, a thick mash is usually desired because the first wort gravity is nice and high, the mash bed floats atop the high-gravity wort, and the low ratio of water to malt keeps the concentration of mash enzymes and their starchy substrates high. The latter point is important to enzyme kinetics as the rate of enzymatic reactions is directly related to the concentrations of substrates and enzymes. An enzyme is also less prone to thermal denaturation when attached to its substrate; this is one reason why the optimal temperatures for a given enzyme are over a temperature range, as opposed to a single value.

If brewers could use thick mashes for stirred mashing, many would because a thick mash yields a high first wort gravity. But when a mash is stirred and then pumped to a lauter tun, or pumped to a decoction kettle, a thinner mash is simply easier to handle (I am referring to commercial equipment here). This is why many recipes for lagers use thinner mashes. I believe, and present as an argument in this answer, that commercial brewers choose to thin their mashes out for a combination of reasons that include: Ease of mash handling, improved extract yield, reduced sparge water volume, influence on wort fermentability, and influence on beer flavor. As long as mash pH and the concentration of calcium ions are kept in the ideal range (keep reading), an extremely thin mash should not be the root cause of brewing failure.

The BIAB method employs thin mashes for the same basic reasons other brewing technologies use thin mashes: Functionality. The primary distinction between the BIAB method and other brewing methods, aside from the simple equipment, is the lack of sparging. Brewers using a brewhouse with a mash tun or lauter tun can, of course, do the same using their brewing set-ups. Kirin Ichiban, anyone? The thin mash used in the BIAB method allows brewers to produce a full volume of wort without messing around with sparging or adding any water after beginning the mash. But with this thin mash comes a dilution of the buffering systems that control mash pH, and a dilution of calcium ion concentration.

Without knowing more about your brews, it is impossible to know the cause of the failures, but focusing on your water is important, especially given your location. Indianapolis water comes from limestone aquifers and contains a lot of carbonate. This type of water often results in a mash pH that is outside of the ideal pH range of 5.2–5.5. And since thin mashes contain more water minerals and less mash buffers, mainly amino acids and phosphates, than thick mashes, high carbonate water is more problematic in these thin mashes. Your water contains plenty of calcium, but if you were using water with a low calcium content, for example reverse osmosis (RO) water, you would want to make sure that you have at least 50 mg/L of calcium in the mash water because calcium thermally stabilizes alpha-amylase.

I am a big fan of using RO water for brewing because it makes water adjustment easier. But there are many brewers who prefer using their local water. No problem with doing this, but more attention is required. At a bare minimum, a pH meter should be used to monitor mash and wort pH. The mash pH should fall between 5.2–5.5. This pH range is important for enzyme activity; if the pH is too high or too low, starch conversion, wort fermentability, and wort separation can all be negatively influenced. Wort pH during sparging (obviously, not for BIAB brewers) should also be monitored when using water high in carbonates because wort pH increases as gravity drops, and with this can come more tannins; it is normal for brewers to stop collecting wort when the gravity is less than 2 ˚Plato/1.008 or when the pH rises above 5.8–6.0. Although mash pH, and the wort pH that flows from the mash during wort collection for brewers using mash tuns, can be adjusted by adding different salts to the mash system, it is easier to adjust mash pH using either lactic or phosphoric acid.

In the summary of your problems, you mention that your first brew seemed “flabby.” This is a wine term used to describe wines lacking acidity; a flabby wine lacks structure and is appropriately labeled by this funny term. Although this moniker is sometimes used for beer, it is not something that most brewers have in their lexicon . . . maybe your question will result in a spike of this quirky term! The useful thing about this descriptor is that it has a direct connection to process. A flabby beer can be converted into a crisp beer by keeping the pH of the mash, and especially the wort, on the low end of the ideal range. This is best done when brewing, as opposed to attempting to tone the body of a flabby beer by adding acid. One very effective brewing technique is to adjust wort pH at kettle-fill, before the boil begins. This method makes for a cleaner hop bitterness, and really helps to make a crisp beer when brewing styles like Pilsner and Kölsch.

Don’t hang up your mash bag too quickly! I was a skeptic of this method when it first came on the scene because it is so different from other mashing methods, but tasting great beers made from the BIAB technique has changed my opinion. It may take you several more batches to exorcise the demons from your BIAB brews, but you should be able to dial this method in to help you reap its benefits of reducing brewing time and using less equipment.

Response by Ashton Lewis.