As our fermentations progress there are a number of additions that we have to make to our tanks during this busy wine making period. Possibly one of the most important is the ‘fining agent’, added to clarify and stabilise the finished wine. There are a number of different fining agents available, and these are usually applied according to the type of wine or perhaps even the characteristics of a particular grape variety. For example, egg whites are commonly used for red wines as they have the effect of reducing harsh tannins, and some even claim, add a certain silkiness. Another common fining agent in gelatine, which not only clarifies wine, but can also reduce astringency – this is often used in conjunction with kieselsol, that can also help to reduce bitterness.Of course the downside of both egg whites and gelatine is that it renders the finished wine unsuitable for vegetarians.

At Castro Martin we chose perhaps the most commonly used fining agent – Bentonite. Many deposits of this volcanic clay material are found in the USA, especially in Wyoming. Indeed, the name itself is derived from Fort Benton where an American geologist discovered the first deposits around 100 years ago. In Europe, bentonite occurs and is mined in the Mediterranean region and in Lower Bavaria, Germany.

The dried bentonite powder is mixed into a thick, smooth paste and then diluted with a little fermenting grape juice before being added back to the tank. It is then mixed thoroughly with the developing wine. At this point the fermenting must carries a lot of suspended matter (such as dead yeast cells and grape fragments) that would potentially render the finished wine dull or even cloudy. The bentonite forms an ionic bond with these suspended particles, in effect weighing them down, so that over time they will gradually fall by gravity and settle at the bottom of the tank. (This deposit, containing the yeast cells, is known as the ‘lees’). Not only does this leave the wine clean and bright, but bentonite also absorbs some of the proteins and bacteria that can be harmful to the future development of the wine. For example, some proteins can cause haziness if the wine is exposed to a higher temperature after bottling.

As you can see, there is quite a bit of science involved in the wine making process….. much more than simply adding a bit of yeast and hoping for the best!

As our fermentations progress there are a number of additions that we have to make to our tanks during this busy wine making period. Possibly one of the most important is the ‘fining agent’, added to clarify and stabilise the finished wine. There are a number of different fining agents available, and these are usually applied according to the type of wine or perhaps even the characteristics of a particular grape variety. For example, egg whites are commonly used for red wines as they have the effect of reducing harsh tannins, and some even claim, add a certain silkiness. Another common fining agent in gelatine, which not only clarifies wine, but can also reduce astringency – this is often used in conjunction with kieselsol, that can also help to reduce bitterness.Of course the downside of both egg whites and gelatine is that it renders the finished wine unsuitable for vegetarians.

At Castro Martin we chose perhaps the most commonly used fining agent – Bentonite. Many deposits of this volcanic clay material are found in the USA, especially in Wyoming. Indeed, the name itself is derived from Fort Benton where an American geologist discovered the first deposits around 100 years ago. In Europe, bentonite occurs and is mined in the Mediterranean region and in Lower Bavaria, Germany.

The dried bentonite powder is mixed into a thick, smooth paste and then diluted with a little fermenting grape juice before being added back to the tank. It is then mixed thoroughly with the developing wine. At this point the fermenting must carries a lot of suspended matter (such as dead yeast cells and grape fragments) that would potentially render the finished wine dull or even cloudy. The bentonite forms an ionic bond with these suspended particles, in effect weighing them down, so that over time they will gradually fall by gravity and settle at the bottom of the tank. (This deposit, containing the yeast cells, is known as the ‘lees’). Not only does this leave the wine clean and bright, but bentonite also absorbs some of the proteins and bacteria that can be harmful to the future development of the wine. For example, some proteins can cause haziness if the wine is exposed to a higher temperature after bottling.

As you can see, there is quite a bit of science involved in the wine making process….. much more than simply adding a bit of yeast and hoping for the best!