As homebrewers, replicating a recipe consistently is much more difficult than the recipe for our favorite lasagna. The key to successfully reproducing a beer? Accurate, precise measurements.

When you know the exact inputs (ingredients, time, temperature, etc.) that create an output (really excellent homebrew), repeating the process is easy. The thing is, there are so many elements to pay attention to during the brewing process that sometimes specific measurements are not taken properly or are neglected all together.

The metrics below are key to minimizing the variations between batches of homebrew.

Pitch Rate

The pitch rate is how many yeast cells a brewer will use to ferment a specific volume and gravity of wort. A general guide for pitch rate is 1 million viable yeast cells per degree plato (°P) per milliliter (mL) of wort. (For example 15 million yeast cells per mL of 15°P wort.) Lagers lean a bit higher (about 1.5 million cells per mL per °P) and ales can dip slightly lower (.75 million cells per mL per °P) Using a consistent pitch rate is the first step to having uniform fermentation characteristics. The most reliable way to calculate pitch rate is by making a yeast starter a day or two before brew day. A yeast starter is a sugar solution that is used to grow a specific number of yeast cells to an exact amount that will be pitched to start fermentation.

A starter calculator, like this one from Brewer’s Friend, takes into account both the vitality of the yeast (calculated based on age of yeast in the package) and the cell count required by the volume of beer being brewed. The total number of yeast cells pitched into wort determines how much work each individual cell will have to do and therefore how much stress it is under. These stress levels regulate flavor production of positive flavors like esters as well as less desirable flavors like sulfur compounds.

To make the starter, both the water and dextrose should be measured by weight instead of volume for the most accurate result. (One milliliter of water by volume is equal to one gram of water by weight.) The weight of both water and dextrose will fluctuate based on the amount of growth required in the starter. The final yeast cell count will be the same.

Ingredient Weights

For the most consistent results, brewing ingredients should be weighed instead of eyeballed in volume. “One bucket of grain” is hard to replicate. A scale with +/- 0.01oz accuracy is inexpensive and will immediately make all of your grain and water measurements uniform.

If you’re planning to use water chemicals and yeast nutrients, investing in a highly accurate scale (+/- 0.01g) is a good idea. Some chemicals that improve beer can be toxic to yeast at high levels. For example, you want about 0.2mg/L of zinc (usually added as yeast nutrient) in wort for healthy fermentation but at around 0.6 mg/L zinc becomes toxic to yeast and will slow growth. This smaller, more accurate scale is also optimal for measuring hops. Remember the alpha acid concentration (AA%) in each pack of hop pellets will vary, so be sure to weigh for the proper quantity of alpha acid instead of hop matter. These two scales will not only have you adding ingredients more systematically, you can also get rid of all the mismatched measuring cups and buckets with handwritten markings that you were using before (RIP my yeast nutrient spoon!).

pH

pH is a figure that expresses the acidity or alkalinity of a solution, in our case that solution is beer or wort. The most critical time to measure pH is during the mash. The enzymes that break down starches in wort perform best in an environment with a pH between 5.1 and 5.5 (most brewers aim for 5.2 as the ideal sweet spot). Beyond starch conversion, pH is also important in protein coagulation that happens during the boil, and the isomerization of hop alpha acids.

When the mash is conducted in the ideal pH range, the pH for the following steps will fall into place as long as the sparge water pH is not drastically different from the pH of the brewing liquor.

pH can be measured by a homebrewer several ways. The most common are pH strips and a handheld pH meter. The pH meter will be more exact, but it is also more expensive. No matter which device is used, pH measurements fluctuate based on temperature, so it is required to cool the sample to room temperature to get an accurate measurement. If the goal is to take pH readings on the fly at mash temperatures, pH meters with a temperature probe are another suitable option. These tools will automatically adjust pH readings for temperature, but they are even more expensive.

Another time to test pH for consistent brews is the finished beer pH. Carbon dioxide has a large impact on pH, so samples should be degassed before taking a reading. (To degas a beer, simply put it in a very clean blender until it is flat when poured.)

Final beer pH will usually measure between 4.2 and 4.8 with ales at the lower end of that spectrum. The most important part of final beer pH is hitting the same number consistently. Slight pH fluctuations have an outsized effect on flavor, and though it isn’t common commercially, you can correct the pH of final beers. Drops of phosphoric acid are the most common way to lower final beer pH as they have a low impact on flavor and the acid is more stable than other available acids.

Temperature

An accurate thermometer is essential to all steps of brewday and fermentation. Many kettles made specifically for brewing come with a temperature probe with an easy-to-read display attached. To calibrate this probe, and for all other temperature needs, the Thermapen instant read thermometer takes very accurate, fast, and reliable readings. (They’re expensive upfront but I’ve been using mine for more than five years.)

Temperature readings should be taken for strike water, mashing, and chilling as well as daily throughout fermentation. When it comes to repeatability, fermentation temperature has a huge impact on the flavor balance of a beer, especially when working with expressive yeast like Belgian or German wheat strains.

At the end of fermentation, temperature should be measurably increased to clean up flavors like diacetyl and acetaldehyde. A 3-4 degree Fahrenheit increase for three days will allow the yeast to convert those unwanted flavors so they won’t be present in the final beer.

Specific Gravity

Specific gravity is the measurement of a liquid’s density relative to pure water. In the case of wort and beer, the materials adding to the density are sugars, unfermentable starches, and proteins.

Both professional brewers and homebrewers take gravity measurements with a hydrometer, a glass tube with a large bottom bulb and a thin neck marked with graduation markings.

This gravity is temperature sensitive, so it’s vital that the liquid sample is cooled to the same temperature each time it is assessed. To take a reading, place the hydrometer into the liquid and give it a good spin. The spinning motion displaces any air bubbles that may be attached to the hydrometer, giving it buoyancy and throwing off the measurement. Once the hydrometer stops spinning, take the gravity reading from the bottom of the meniscus.

Refractometers can also be used to measure gravity but they are less reliable, especially when it comes to dark beer. This is because they measure the gravity of a liquid by the way, or specific angle to which, it refracts light. Since they are about the same price as a hydrometer, stick with the easier-to-read tool.

Gravity measurements should be taken at least three times during the fermentation process: as soon as the yeast is pitched (this is known as the OG or Original Gravity reading), again when fermentation starts to slow, and finally when fermentation ceases completely (this is known as the FG or Final Gravity reading).

A sample size about the size of a half pint is required to take a gravity reading, so it is important to be judicious with how often measurements are taken, lest you end up with no beer to drink.